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title: "Adamantinomatous Craniopharyngioma"
docid: "495ef4ba-399a-4096-aeb2-f466ab5abc32"
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pageDescription: "Adamantinomatous Craniopharyngioma"
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---
## KEY FACTS
- ### Terminology
- Benign, partially cystic sellar region tumor derived from remnants of craniopharyngeal duct/Rathke pouch epithelium
- 2 types
- Adamantinomatous (cystic mass in childhood)
- Papillary (solid or solid/cystic mass in older adults)
- ### Imaging
- General features
- Multilobulated, often large (> 5-cm) sellar/suprasellar mass
- Occasionally giant, multicompartmental
- CT: Cystic (90%), Ca⁺⁺ (90%), enhancing (90%)
- MR: Signal varies with cyst contents
- Cysts variably hyperintense on T1WI and T2WI
- Solid portions enhance heterogeneously; cyst walls enhance strongly
- Cyst contents show broad lipid peak (0.9-1.5 ppm) on MR spectroscopy
- ### Top Differential Diagnoses
- Rathke cleft cyst
- Suprasellar arachnoid cyst
- Hypothalamic/chiasmatic astrocytoma
- Germinoma or mixed germ cell tumor
- Pituitary adenoma/pituitary neuroendocrine tumor
- Thrombosed aneurysm
- Epidermoid/dermoid tumors
- ### Pathology
- Most common pediatric nonglial intracranial tumor
- WHO grade 1
- ### Clinical Issues
- Bimodal age distribution
- Peak: 5-15 years; adults: 45-60 years
- Pediatric patient with morning headache, visual defect, short stature
- Endocrine disturbances include growth hormone (GH) deficiency, luteinizing hormone (LH)/follicle-stimulating hormone (FSH) deficiency
- Others = hypothyroidism > adrenal failure > diabetes insipidus
- Surgical resection is primary therapy
- Surgery, radiation therapy, or cyst aspiration for recurrent tumors
## TERMINOLOGY
- ### Abbreviations
- Craniopharyngioma (CP)
- Adamantinomatous CP (AdCP)
- Papillary CP (PaCP)
- ### Synonyms
- Older terms: Craniopharyngeal duct tumor, Rathke pouch tumor, adamantinoma
- ### Definitions
- Benign, partially cystic sellar region tumors derived from Rathke pouch epithelium
- 2 distinct tumor types in 2021 WHO: Adamantinomatous and papillary
- **AdCP**: Mixed solid and cystic squamous epithelial tumor
- **PaCP**: Solid or partially cystic nonkeratinizing squamous epithelial tumor
## IMAGING
- ### General Features
- #### Best diagnostic clue
- CT: Partially Ca⁺⁺ mixed solid/cystic suprasellar mass in child
- MR: Complex signal intensity suprasellar mass
- #### Location
- Surgical division of CPs into 3 groups
- Sellar
- Prechiasmatic
- Retrochiasmatic
- Imaging locations of AdCP
- Suprasellar (20-40%)
- Suprasellar + intrasellar component (50-75%)
- Entirely intrasellar (5%)
- Often extends into multiple cranial fossae: Anterior (9%), middle (8%), posterior, &/or retroclival (12%)
- Rare ectopic CP locations
- Optic chiasm, 3rd ventricle
- Other: Nasopharynx, paranasal sinuses, pineal gland, sphenoid (clivus), cerebellopontine angle
- #### Size
- Variable; often large at presentation (> 5 cm)
- Occasionally giant, multicompartmental
- #### Morphology
- Multilobulated, multicystic
- ### CT Findings
- #### NECT
- AdCP (90% rule)
- 90% mixed solid (isodense), cystic (hypodense)
- 90% calcify
- 90% enhance (solid = nodule; rim = capsule)
- Enlargement of sella turcica uncommon
- ### MR Findings
- #### T1WI
- Signal varies with cyst contents
- T1 hyperintense due to high protein content, cholesterol
- Classic: Hyperintense cyst + heterogeneous nodule
- #### T2WI
- Cysts are variably hyperintense
- Solid component = heterogeneous (iso-/hyperintense, Ca⁺⁺ portions hypointense)
- Hyperintense signal in brain parenchyma adjacent to tumor may indicate
- Gliosis, tumor invasion, irritation from leaking cyst fluid
- Edema from compression of optic chiasm/tracts
- Hypointense T2* = Ca⁺⁺
- #### FLAIR
- Cyst contents typically hyperintense
- #### DWI
- Variable, depending upon character of cyst fluid
- #### T1WI C+
- Solid portions enhance heterogeneously; cyst walls enhance strongly
- #### MRA
- Vascular displacement &/or encasement
- #### MRS
- Cyst contents show broad lipid spectrum (0.9-1.5 ppm)
- ### Imaging Recommendations
- #### Best imaging tool
- MR with thin sagittal, coronal sequences
- #### Protocol advice
- Pre-/postcontrast T1WI, T2, FLAIR, GRE, DWI
## DIFFERENTIAL DIAGNOSIS
- [Rathke Cleft Cyst](/document/rathke-cleft-cyst/a5a3a735-ad86-4fd2-bcb8-2181c48ba3da)
- Noncalcified, less heterogeneous
- Look for intracystic nodule on T2
- Does not enhance
- Claw sign (enhancing pituitary draped around cyst)
- Small Rathke cleft cyst (RCC) may be indistinguishable from rare intrasellar CP
- RCCs express CK8 and CK20 (CPs generally do not)
- ### Suprasellar Arachnoid Cyst
- No Ca⁺⁺, enhancement
- Follows CSF on all MR sequences
- ### Hypothalamic/Chiasmatic Astrocytoma
- Solid or with small cystic/necrotic components
- Ca⁺⁺ is rare; robust enhancement is common
- [Germinoma or Mixed Germ Cell Tumor](/document/germinoma/69ff4834-1d53-4e17-8fa2-2134b9db2802)
- CSF spread is common; Ca⁺⁺ is rare
- Enhancing midline mass, pineal or suprasellar
- ### Pituitary Adenoma/Pituitary Neuroendocrine Tumor
- Rare in prepubescent children
- Isointense with brain
- Enhances strongly
- Can mimic AdCP when cystic and hemorrhagic
- ### Epidermoid/Dermoid Tumors
- Epidermoid: DWI bright; follows CSF on T1, T2
- Dermoid: Midline cystic lesion with T1-hyperintense fat
- Minimal or no enhancement
- ### Thrombosed Aneurysm
- Contains blood products; use GRE/SWI
- Look for residual patent lumen, phase artifact
## PATHOLOGY
- ### General Features
- #### Etiology
- 2 proposed theories
- CPs arise from remnants of craniopharyngeal duct and Rathke pouch epithelium
- CPs arise from squamous epithelial cells in pars tuberalis of adenohypophysis
- #### Genetics
- No known genetic susceptibility (rare reports of siblings, parent-child)
- Small subset of CPs are monoclonal tumors that arise from oncogenes at specific loci
- *CTNNB1* mutations and aberrant nuclear expression of β-catenin in up to 95% of cases
- Occasional familial adenomatous polyposis 1-associated cases (lack *CTNNB1* mutations)
- ### Staging, Grading, & Classification
- WHO grade 1
- MIB-1 labeling index > 7% predicts recurrence
- ### Gross Pathologic & Surgical Features
- Solid tumor with variable cysts
- Adamantinomatous cysts often contain thick "crankcase oil" fluid
- Epithelial fronds penetrate adjacent hypothalamus/chiasm
- ### Microscopic Features
- Adamantinomatous (mostly pediatric)
- Multistratified squamous epithelium with nuclear palisading
- Nodules of "wet" keratin
- Dystrophic Ca⁺⁺
- Malignant transformation, distant metastases rare
- May occur with varied histologies, resulting in poor prognosis
## CLINICAL ISSUES
- ### Presentation
- #### Most common signs/symptoms
- Symptoms vary with location, size of tumor, age of patient
- Visual disturbances (60-85%)
- Bitemporal hemianopsia
- #### Other signs/symptoms
- Endocrine disturbances (52-87%)
- Growth hormone (GH) deficiency (75%) > luteinizing hormone (LH)/follicle-stimulating hormone (FSH) deficiency > hypothyroidism > adrenal failure > diabetes insipidus
- Headaches
- Cognitive impairment
- #### Clinical profile
- Pediatric patient with morning headache, visual defect, short stature
- ### Demographics
- #### Age
- Bimodal distribution (peak: 5-15 years with smaller peak at 45-60 years)
- #### Sex
- M = F
- #### Epidemiology
- CP: Comprise 1.2-4.6% of all intracranial tumors across all ages
- Incidence = 0.5-2.5 new cases per 1 million per year
- AdCP: Most common pediatric intracranial tumor of nonglial origin
- Account for nearly all CPs in children; 80% of CPs in adults
- 6-11% of all pediatric intracranial tumors
- ~ 54% of all pediatric sellar/chiasmatic region tumors are CPs
- ### Natural History & Prognosis
- Typically slow-growing, benign neoplasm
- Prognosis based upon size, extent of tumor at presentation
- < 5 cm, recurrence rate: 20%
- > 5 cm, recurrence rate: 83%
- Overall 10-year survival: 40-93%
- ### Treatment
- Methods of primary treatment
- Radical surgery = gross total resection
- Complications = hypothalamic injury, endocrine symptoms, vasa vasorum injury, and pseudoaneurysm
- Surgery may occur via craniotomy, transnasal, transorbital, or endoscopic routes
- Less invasive surgery = subtotal resection + radiation therapy
- Biopsy, cyst drainage, and radiation therapy
- Treatment for residual or recurrent tumor
- Surgery, radiation therapy, or cyst aspiration
- Cyst instillation with intracavitary radioisotopes, bleomycin, or other sclerosing agents
## DIAGNOSTIC CHECKLIST
- ### Consider
- Preoperative ophthalmologic and endocrine evaluations
- ### Image Interpretation Pearls
- Use NECT to detect Ca⁺⁺ if MR diagnosis is in question
- AdCP = 90% rule (90% cystic, calcified, enhancing)
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## References
## Selected References
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## Images
### Selected Images
![Sagittal graphic shows a predominantly cystic, partially solid <img src='img/arrows/WO.png' alt='white open arrow'/> suprasellar mass with focal rim Ca⁺⁺. Note the small intrasellar component <img src='img/arrows/WS.png' alt='white solid arrow'/> and fluid-fluid level. Craniopharyngiomas (CPs) are the 90% tumors (90% cystic, 90% Ca⁺⁺, and 90% enhancing).](images/app.statdx.com_image_thumbnail_e2778122-4aaf-4b6b-9bde-13035ad2edc2_annotated_true_size_900_quality_90_45fe4e276dd73e85fe75254155ec71866efc2ba3.jpg)
*Sagittal graphic shows a predominantly cystic, partially solid <img src='img/arrows/WO.png' alt='white open arrow'/> suprasellar mass with focal rim Ca⁺⁺. Note the small intrasellar component <img src='img/arrows/WS.png' alt='white solid arrow'/> and fluid-fluid level. Craniopharyngiomas (CPs) are the 90% tumors (90% cystic, 90% Ca⁺⁺, and 90% enhancing).*
![Sagittal graphic shows a predominantly cystic, partially solid <img src='img/arrows/WO.png' alt='white open arrow'/> suprasellar mass with focal rim Ca⁺⁺. Note the small intrasellar component <img src='img/arrows/WS.png' alt='white solid arrow'/> and fluid-fluid level. Craniopharyngiomas (CPs) are the 90% tumors (90% cystic, 90% Ca⁺⁺, and 90% enhancing).](images/app.statdx.com_image_thumbnail_e2778122-4aaf-4b6b-9bde-13035ad2edc2_size_174_quality_85_c7fb494948b28f6cdf304061045a0ea383802f51.jpg)
*Sagittal graphic shows a predominantly cystic, partially solid <img src='img/arrows/WO.png' alt='white open arrow'/> suprasellar mass with focal rim Ca⁺⁺. Note the small intrasellar component <img src='img/arrows/WS.png' alt='white solid arrow'/> and fluid-fluid level. Craniopharyngiomas (CPs) are the 90% tumors (90% cystic, 90% Ca⁺⁺, and 90% enhancing).*
![Sagittal T2 MR in a 9-year-old with headache and visual changes shows a heterogeneous cystic and solid sellar and suprasellar CP <img src='img/arrows/CO.png' alt='cyan open arrow'/> with anterior extension into the sphenoid sinus <img src='img/arrows/WS.png' alt='white solid arrow'/> and superior displacement of the optic chiasm.](images/app.statdx.com_image_thumbnail_cffd0b67-0dae-4e97-b948-9b2fd0168331_annotated_true_size_900_quality_90_d78db4143e5230eb38e02113ea74d06ba8dde635.jpg)
*Sagittal T2 MR in a 9-year-old with headache and visual changes shows a heterogeneous cystic and solid sellar and suprasellar CP <img src='img/arrows/CO.png' alt='cyan open arrow'/> with anterior extension into the sphenoid sinus <img src='img/arrows/WS.png' alt='white solid arrow'/> and superior displacement of the optic chiasm.*
![Sagittal T1 MR in a 44-year-old shows a heterogeneous sellar and suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/>. Note mild enlargement of the sella turcica with flattening of the pituitary gland <img src='img/arrows/WS.png' alt='white solid arrow'/> beneath the adamantinomatous CP (AdCP).](images/app.statdx.com_image_thumbnail_7685d625-95f1-4b89-9bd8-38493bb0a272_annotated_true_size_900_quality_90_7aaa6f313c2cb285b8db448174f6984618aa51ba.jpg)
*Sagittal T1 MR in a 44-year-old shows a heterogeneous sellar and suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/>. Note mild enlargement of the sella turcica with flattening of the pituitary gland <img src='img/arrows/WS.png' alt='white solid arrow'/> beneath the adamantinomatous CP (AdCP).*
![Sagittal T1 C+ MR in a 45-year-old woman shows a cystic and solid mass with an enhancing portion <img src='img/arrows/CO.png' alt='cyan open arrow'/>, which distinguishes this cystic lesion as a CP, not a Rathke cleft cyst. Surgical resection is the primary therapy for this WHO grade 1 neoplasm. However, the recurrence rate at 10 years approaches 20%.](images/app.statdx.com_image_thumbnail_a9f940c7-bf5d-4ec9-b5d0-72712ed14af4_annotated_true_size_900_quality_90_cf0c87e533a1c57eaea7c325c3f85d987dbbc5ec.jpg)
*Sagittal T1 C+ MR in a 45-year-old woman shows a cystic and solid mass with an enhancing portion <img src='img/arrows/CO.png' alt='cyan open arrow'/>, which distinguishes this cystic lesion as a CP, not a Rathke cleft cyst. Surgical resection is the primary therapy for this WHO grade 1 neoplasm. However, the recurrence rate at 10 years approaches 20%.*
![Sagittal CT in a 65-year-old shows a sellar and suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/> with associated Ca⁺⁺. Although most common in pediatric patients, AdCPs make up the majority (80%) of CP in adults.](images/app.statdx.com_image_thumbnail_0c185659-c099-4aea-b06b-213bb25e7e93_annotated_true_size_900_quality_90_2dc767839a01e23ba1fd443290106242d3bec4f6.jpg)
*Sagittal CT in a 65-year-old shows a sellar and suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/> with associated Ca⁺⁺. Although most common in pediatric patients, AdCPs make up the majority (80%) of CP in adults.*
![Coronal T2 MR in a 2-year-old with a huge suprasellar mass shows multiple hyperintense cysts <img src='img/arrows/CS.png' alt='cyan solid arrow'/>. AdCP typically present between 5-15 years in childhood and between 45-60 years in adults. They are the most common pediatric intracranial tumor of nonglial origin.](images/app.statdx.com_image_thumbnail_3d96e315-5e46-4624-8ea8-49f2eb123d14_annotated_true_size_900_quality_90_b457c6f320730cf64f417afef363d6d2b35eb14c.jpg)
*Coronal T2 MR in a 2-year-old with a huge suprasellar mass shows multiple hyperintense cysts <img src='img/arrows/CS.png' alt='cyan solid arrow'/>. AdCP typically present between 5-15 years in childhood and between 45-60 years in adults. They are the most common pediatric intracranial tumor of nonglial origin.*
![Axial NECT shows classic findings of an AdCP. Note the large suprasellar cyst with a fluid-fluid level <img src='img/arrows/WO.png' alt='white open arrow'/>, rim <img src='img/arrows/CC.png' alt='cyan curved arrow'/>, and globular <img src='img/arrows/CS.png' alt='cyan solid arrow'/> Ca⁺⁺. Enhancement was present on postcontrast images.](images/app.statdx.com_image_thumbnail_9d0889eb-0ea4-4d99-a13e-8fbf23f49107_annotated_true_size_900_quality_90_59b1c802239dc0db4ad679357f6e8cdc0592cabe.jpg)
*Axial NECT shows classic findings of an AdCP. Note the large suprasellar cyst with a fluid-fluid level <img src='img/arrows/WO.png' alt='white open arrow'/>, rim <img src='img/arrows/CC.png' alt='cyan curved arrow'/>, and globular <img src='img/arrows/CS.png' alt='cyan solid arrow'/> Ca⁺⁺. Enhancement was present on postcontrast images.*
![Sagittal gross pathology shows classic AdCP with mixed solid, cystic components. The classic machine or &quot;crankcase oil&quot; <img src='img/arrows/WO.png' alt='white open arrow'/> is present. Note the intrasellar extension <img src='img/arrows/WC.png' alt='white curved arrow'/>. (Courtesy R. Hewlett, MD.)](images/app.statdx.com_image_thumbnail_ba6d9fa9-36be-4883-9360-0dc2163bbb8c_annotated_true_size_900_quality_90_85a6d8b044990684909f2f12437b071454c8a176.jpg)
*Sagittal gross pathology shows classic AdCP with mixed solid, cystic components. The classic machine or &quot;crankcase oil&quot; <img src='img/arrows/WO.png' alt='white open arrow'/> is present. Note the intrasellar extension <img src='img/arrows/WC.png' alt='white curved arrow'/>. (Courtesy R. Hewlett, MD.)*
![Sagittal T1 MR in a 7-year-old shows a cystic <img src='img/arrows/CS.png' alt='cyan solid arrow'/> and solid <img src='img/arrows/WO.png' alt='white open arrow'/> suprasellar mass with a small fluid-fluid level <img src='img/arrows/BS.png' alt='black solid arrow'/> and enlargement of the sella turcica. The T1 hyperintensity is related to high protein content or cholesterol.](images/app.statdx.com_image_thumbnail_6b727d42-ec72-4c27-9316-64cbb2e4f561_annotated_true_size_900_quality_90_8f26ffaceec6e1ef123e4d200c2b0e26862f1a28.jpg)
*Sagittal T1 MR in a 7-year-old shows a cystic <img src='img/arrows/CS.png' alt='cyan solid arrow'/> and solid <img src='img/arrows/WO.png' alt='white open arrow'/> suprasellar mass with a small fluid-fluid level <img src='img/arrows/BS.png' alt='black solid arrow'/> and enlargement of the sella turcica. The T1 hyperintensity is related to high protein content or cholesterol.*
![Coronal T1 C+ MR in a 62-year-old shows a heterogeneously enhancing sellar and suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/>. These WHO grade 1 tumors are typically slow-growing, benign neoplasms with an excellent prognosis. Recurrence rate is related to size of the original tumor and the extent of resection.](06663ffd-bb6a-4ad9-aaae-de9bdc19f9ec)
*Coronal T1 C+ MR in a 62-year-old shows a heterogeneously enhancing sellar and suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/>. These WHO grade 1 tumors are typically slow-growing, benign neoplasms with an excellent prognosis. Recurrence rate is related to size of the original tumor and the extent of resection.*
### Additional Images
![Axial T1 C+ MR in a child with a huge multilobulated CP shows rim <img src='img/arrows/WS.png' alt='white solid arrow'/> and solid nodular <img src='img/arrows/WO.png' alt='white open arrow'/> enhancement. Note that the cyst fluid is moderately hyperintense compared to CSF in the lateral ventricles.](cc06740c-8876-4731-902d-f61c06feca2c)
*Axial T1 C+ MR in a child with a huge multilobulated CP shows rim <img src='img/arrows/WS.png' alt='white solid arrow'/> and solid nodular <img src='img/arrows/WO.png' alt='white open arrow'/> enhancement. Note that the cyst fluid is moderately hyperintense compared to CSF in the lateral ventricles.*
![Axial DWI MR in the same patient with a large CP shows no restriction in the fluid-containing part of the tumor <img src='img/arrows/WS.png' alt='white solid arrow'/>.](fa255b54-db83-4f62-8fcb-92f90dc7b566)
*Axial DWI MR in the same patient with a large CP shows no restriction in the fluid-containing part of the tumor <img src='img/arrows/WS.png' alt='white solid arrow'/>.*
![Axial NECT shows a low-attenuation suprasellar mass with rim <img src='img/arrows/WS.png' alt='white solid arrow'/> and globular <img src='img/arrows/WC.png' alt='white curved arrow'/> Ca⁺⁺. Note the fluid-fluid level formed by intracystic keratin debris <img src='img/arrows/WO.png' alt='white open arrow'/>.](3da58631-1f82-47b6-add0-65ebba8d298a)
*Axial NECT shows a low-attenuation suprasellar mass with rim <img src='img/arrows/WS.png' alt='white solid arrow'/> and globular <img src='img/arrows/WC.png' alt='white curved arrow'/> Ca⁺⁺. Note the fluid-fluid level formed by intracystic keratin debris <img src='img/arrows/WO.png' alt='white open arrow'/>.*
![Sagittal T1 MR shows a complex predominantly cystic suprasellar mass. Note the T1 shortening within the cyst due to machine oil-like proteinaceous fluid <img src='img/arrows/WS.png' alt='white solid arrow'/>.](ed0c967d-3c62-41c2-866e-790bef814a95)
*Sagittal T1 MR shows a complex predominantly cystic suprasellar mass. Note the T1 shortening within the cyst due to machine oil-like proteinaceous fluid <img src='img/arrows/WS.png' alt='white solid arrow'/>.*
![Axial NECT shows a predominantly solid, minimally calcified <img src='img/arrows/WS.png' alt='white solid arrow'/> suprasellar CP.](7160473b-a80c-4244-8ae5-8e74760ba18b)
*Axial NECT shows a predominantly solid, minimally calcified <img src='img/arrows/WS.png' alt='white solid arrow'/> suprasellar CP.*
![Sagittal T1 C+ MR shows a principally cystic sellar/suprasellar mass with rim enhancement <img src='img/arrows/WS.png' alt='white solid arrow'/>.](c2e8233b-b441-4961-8e3a-ed52422ef926)
*Sagittal T1 C+ MR shows a principally cystic sellar/suprasellar mass with rim enhancement <img src='img/arrows/WS.png' alt='white solid arrow'/>.*
![Sagittal T1 C+ MR in a 48-year-old man with visual changes shows an enhancing nodule <img src='img/arrows/WO.png' alt='white open arrow'/>, which distinguishes this cystic lesion as a CP, not a Rathke cleft cyst. Surgical resection is the primary therapy for this WHO grade 1 neoplasm; however, the recurrence rate at 10 years approaches 20%.](6e55062a-dfd3-4e71-a284-f09f38a83540)
*Sagittal T1 C+ MR in a 48-year-old man with visual changes shows an enhancing nodule <img src='img/arrows/WO.png' alt='white open arrow'/>, which distinguishes this cystic lesion as a CP, not a Rathke cleft cyst. Surgical resection is the primary therapy for this WHO grade 1 neoplasm; however, the recurrence rate at 10 years approaches 20%.*
![Sagittal T1 C+ MR shows a complex cystic suprasellar mass with an enhancing rim <img src='img/arrows/WC.png' alt='white curved arrow'/> and solid components <img src='img/arrows/WO.png' alt='white open arrow'/>. The cysts contain fluid of different signal intensities. Note the large suprasellar, smaller intrasellar <img src='img/arrows/WS.png' alt='white solid arrow'/> components in this classic CP.](84b0a331-d002-4bca-b2cc-507d0f2c7981)
*Sagittal T1 C+ MR shows a complex cystic suprasellar mass with an enhancing rim <img src='img/arrows/WC.png' alt='white curved arrow'/> and solid components <img src='img/arrows/WO.png' alt='white open arrow'/>. The cysts contain fluid of different signal intensities. Note the large suprasellar, smaller intrasellar <img src='img/arrows/WS.png' alt='white solid arrow'/> components in this classic CP.*
![A short TE (35) H-MRS in a patient with a solid and cystic CP acquired from the center of the cystic portion of the mass shows large lipid-lactate peaks <img src='img/arrows/WS.png' alt='white solid arrow'/>, characteristic of the cholesterol and lipid constituents found in cysts of CPs.](84844193-cd9b-446f-8b38-0be3a17dacfe)
*A short TE (35) H-MRS in a patient with a solid and cystic CP acquired from the center of the cystic portion of the mass shows large lipid-lactate peaks <img src='img/arrows/WS.png' alt='white solid arrow'/>, characteristic of the cholesterol and lipid constituents found in cysts of CPs.*
![Gross pathologic specimen shows a typical solid and cystic composition <img src='img/arrows/BO.png' alt='black open arrow'/> of an AdCP. The cystic spaces contain a thick gelatinous material. (Courtesy AFIP.)](efc60dc9-164a-4864-91af-43f927c25bbc)
*Gross pathologic specimen shows a typical solid and cystic composition <img src='img/arrows/BO.png' alt='black open arrow'/> of an AdCP. The cystic spaces contain a thick gelatinous material. (Courtesy AFIP.)*
docs_md/articles/cavernous-sinus_2a0f0fa0-b60c-4a90-82de-9d78bdf42463.md
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---
title: "Cavernous Sinus"
docid: "2a0f0fa0-b60c-4a90-82de-9d78bdf42463"
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- key: "94f835c8-fa13-4e8a-995b-53048e6b0605"
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pageDescription: "Cavernous Sinus"
pageKeywords: "Head and Neck, Anatomy, Orbit, Cavernous Sinus"
pageTitle: "Cavernous Sinus | STATdx"
enhancedTitle: "Cavernous Sinus"
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---
## TERMINOLOGY
- ### Abbreviations
- Cavernous sinus (CS)
- ### Definitions
- Paired venous lakes with multiple septa within located lateral to sella turcica, pituitary & sphenoid sinus, & medial to mesial temporal lobe
- CSs drain multiple veins from orbit, sylvian fissure, middle & anterior fossa; ultimately provide venous drainage posteriorly & inferiorly via inferior petrosal, superior petrosal, & basilar venous sinuses
- Described as anatomic jewel box due to its complex contents, including several cranial nerves & internal carotid artery (ICA)
- Term cavernous sinus 1st used by Winslow in 1734
## IMAGING ANATOMY
- ### Overview
- Valveless, septated dural venous sinuses of central skull base, present on either side of sella
- Extradural in location communicating with extradural space of spine & orbits, in contrast to other venous sinuses, which are located between 2 layers of dura
- Important given location, relationship to sella, pituitary gland, & internal contents, including multiple cranial nerves & cavernous ICA
- ### Anatomy Relationships
- **Boundaries**
- Boat-shaped structure, narrowest anteriorly & widest posteriorly, bounded by dura with 5 walls, including anterior, posterior, medial, lateral, & superior/roof
- **Superior**: Extends from base of anterior clinoid process to posterior clinoid process
- **Lateral**: Bordered by 2 layers of dura
- **Medial**: Bordered by lateral margin of sella & lateral wall of sphenoid sinus with carotid sulcus
- **Anterior**: Extends to anterior clinoid process & superior orbital fissure (SOF) below it
- **Posterior**: Extends to posterior clinoid process, lateral margin of upper clivus, & petroclival junction, extending laterally to point just medial to trigeminal impression
- **Superior wall/roof**
- Extends from optic strut & SOF anteriorly to petrous apex (PA) & tentorial incisura posteriorly
- Medial margin of roof contiguous with diaphragma sellae
- **Oculomotor triangle**, triangular-shaped portion of CS roof created by 3 dural folds
- Lateral margin of roof separated from lateral wall of CS by cord-like thickening of dura called **anterior petroclinoid fold**that extends from tentorial edge at PA to anterior clinoid process
- Separate fold extends from tentorial edge at PA to posterior clinoid process, **posterior petroclinoid fold**
- Thin band of dura, **interclinoid fold**, extends from anterior clinoid process to posterior clinoid process
- CNIII, along with its sleeve of arachnoid (oculomotor cistern), pierces roof at oculomotor triangle
- CNIV enters posterolateral aspect of oculomotor triangle just posterior to CNIII
- Small portion of roof passes inferomedial to anterior clinoid process where dural roof merges with dura, forming proximal & distal dural rings
- **Lateral wall**
- Sail-shaped dural sheet that extends from SOF & anterior clinoid process anteriorly to PA posteriorly; faces medial temporal lobe
- Consists of thick dural membrane that typically can be dissected into 2 distinct layers
- Thin outer (meningeal) layer
- Thicker inner (endosteal)
- Inner layer envelops oculomotor nerve (CNIII), trochlear nerve (CNIV), ophthalmic (V1) & maxillary (V2) segments of trigeminal nerve
- Lateral & medial walls of CS merge inferiorly along lateral margin of sphenoid, just above maxillary nerve (V2)
- While V3 invested by contiguous dura, not considered component of CS wall
- V2 similar to V3 in regards to CS lateral wall; lies at inferior margin of CS or just outside CS envelope rather than being true component of wall
- Lateral wall merges inferiorly & posteriorly with dura covering Meckel cave
- **Medial wall**
- Consists of upper sellar component & lower sphenoid component
- Upper sellar component of medial wall formed by thin dural membrane, typically single cell layer in thickness that separates venous compartment from lateral margin of pituitary gland
- Inherent weakness of upper sellar component makes it susceptible to invasion from pituitary tumors
- Thicker lower medial wall adherent to carotid sulcus of sphenoid bone
- **Anterior wall**
- Rectangular in shape extending from optic strut, beneath anterior clinoid process laterally to include SOF
- Inferior margin formed by foramen rotundum
- Anterior CS merges with venous plexus in SOF
- **Posterior wall**
- Extends from lateral margin of dorsum sellae to medial aspect of trigeminal impression of PA & superomedial aspect of Meckel cave
- Limited inferiorly by junction of PA & body of sphenoid bone at superomedial aspect of petroclival fissure
- **Dorello canal & CNVI**
- Small gap that separates PA from clivus near medial & superior tip of PA
- Small petrosphenoid ligament of Gruber, crosses from PA tip to base of posterior clinoid process
- Contains venous tissue at confluence of posterior CS & petrosal sinuses
- CNVI passes from prepontine cistern through Dorello canal to enter CS
- **Petrolingual ligament (PLL)**
- Extends from PA to lingula of sphenoid bone
- Invariably surrounds dorsal & lateral walls of lacerum segment of ICA
- Important surgical landmark that marks point at which ICA lacerum segment transitions to cavernous segment
- Also marks inferior & posterior margin of CS
- **Venous communications**
- Venous tributaries
- Superior, inferior ophthalmic veins
- Sphenoparietal sinus
- Communicate with each other via intercavernous plexus (anterior, posterior, & inferior across sella) & basilar venous plexus (across clivus)
- Communicates posteriorly with inferior petrosal sinus, superior petrosal sinus, & basilar venous sinus
- Additional communications with veins of pterygoid venous plexus & skull base foramina (foramen ovale, rotundum, & spinosum, carotid canal, & sphenoidal emissary foramen)
- **Meckel cave**
- Dural outpouching that begins in posterior fossa (porus trigeminus) & extends over petrosphenoid junction into medial & posterior aspect of middle cranial fossa
- Contains part of trigeminal nerve, including trigeminal ganglion
- Superior, anterior, & medial portions of Meckel cave are immediately adjacent to posterior & lateral aspects of CS
- Medial & inferior aspect of Meckel cave is just lateral to ICA as it arises from medial opening of carotid canal & begins to turn vertically & anteriorly into CS
- Trigeminal ganglion positioned in anterior & inferior aspect of Meckel cave, divides into 3 divisions: Ophthalmic (V1), maxillary (V2), & mandibular (V3)
- Ophthalmic division (V1) extends medially & anteriorly & enters lateral wall of CS
- Maxillary division (V2) extends anteriorly, along inferior margin of CS to enter foramen rotundum
- Mandibular division (V3) extends inferiorly & laterally through foramen ovale
- ### Internal Contents
- **CNIII**
- Pierces roof of CS in oculomotor cistern & gets embedded in lateral wall
- Surrounded by thin sleeve of arachnoid & CSF (oculomotor cistern) that travels with nerve for several millimeters to anterior clinoid process
- **CNIV**
- Also pierces roof of CS, & nerve positioned in lateral wall below CNIII
- **V1** (ophthalmic division of CNV) in lateral wall below CNIV
- **V2** (maxillary division of CNV), most inferior cranial nerve in lateral CS wall
- **V3** (mandibular division of CNV) does **not**enter CS proper (passes from Meckel cave inferiorly into foramen ovale)
- **CNVI**lies within CS proper, next to ICA
- Sympathetic fibers travel along ICA within CS
- **Cavernous ICA**
- Bouthillier et al described 7-segment classification system for ICA
- Cervical
- Petrous
- Lacerum
- Cavernous
- Clinoid
- Ophthalmic
- Communicating segments
- Cavernous segment begins as lacerum segment of ICA passes beneath PLL
- Initially ascends & then turns (posterior genu) anteriorly to assume horizontal course through CS
- Posterior genu, usual site of origin for **meningohypophyseal trunk**
- Horizontal portion of cavernous ICA lies within carotid sulcus along lateral margin of sphenoid bone
- Carotid sulcus occasionally dehiscent, allowing ICA to protrude into sphenoid sinus
- Horizontal segment gives rise to **inferolateral trunk,** which supplies tiny branches to intracavernous cranial nerves & tentorium
- Near anterior margin of CS, ICA turns cephalad (anterior genu) & continues medial to anterior clinoid process
- Along this anterior vertical course, ICA passes through 2 anatomically distinct dural rings: Proximal dural ring, which forms true roof of CS anteriorly, & distal dural ring
- Short vertical clinoid segment medial to anterior clinoid process & corresponds to interdural segment of artery between proximal & distal dural rings
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Due to high soft tissue contrast resolution & multiplanar capabilities, MR ± contrast remain imaging modality of choice
- Coronal thin-section high-resolution T2 & T1 weighted sequences
- Axial & coronal T1 fat-saturated thin-section high-resolution sequence after intravenous gadolinium contrast injection
- CT angiogram best for identifying pathology of cavernous ICA & for carotid cavernous fistula
- CT venogram can produce adequate venous-phase contrast enhancement to evaluate for CS thrombosis or thrombophlebitis
- High-resolution bone CT imaging, complementary in evaluation of erosive or destructive pathologies of central skull base
- Conventional angiogram often necessary for diagnosis & treatment of direct & indirect carotid cavernous fistulas as well as cavernous carotid aneurysms
- ### Imaging Pitfalls
- Enhancement of CS can be asymmetric, especially in arterial phase or early venous phase, & should not be mistaken for pathology
- Given presence of multiple potentially enhancing structures in & around CS (CS, pituitary, & ICA), small enhancing lesion, such as perineural tumor spread, may be difficult to discriminate
- Fat can be normally seen anterior in CS near SOF & posterior ICA
- Air foci in CS can be seen on CT from venous emboli resulting from peripheral IV catheter placement
e83d314f-6d23-41e6-bde6-6f6150314e05
## Images
### Graphics
![Axial graphic of sella turcica, as viewed from above, depicts normal sellar and parasellar anatomy. Dura covering right cavernous sinus (CS) is removed to show CNV and CNVI. All cranial nerves are shown in left CS. Mandibular division of CNV does not run through CS but exits from Meckel cave inferiorly to enter foramen ovale. Note CS is not a single venous channel but is extensively septated.](images/app.statdx.com_image_thumbnail_05794198-474c-4ba5-90bd-d67364c4a20d_annotated_false_size_900_quality_90_24bc420f4cf2948be0838844572e9118b8ffa0e4.jpg)
*Axial graphic of sella turcica, as viewed from above, depicts normal sellar and parasellar anatomy. Dura covering right cavernous sinus (CS) is removed to show CNV and CNVI. All cranial nerves are shown in left CS. Mandibular division of CNV does not run through CS but exits from Meckel cave inferiorly to enter foramen ovale. Note CS is not a single venous channel but is extensively septated.*
![Axial graphic of sella turcica, as viewed from above, depicts normal sellar and parasellar anatomy. Dura covering right cavernous sinus (CS) is removed to show CNV and CNVI. All cranial nerves are shown in left CS. Mandibular division of CNV does not run through CS but exits from Meckel cave inferiorly to enter foramen ovale. Note CS is not a single venous channel but is extensively septated.](images/app.statdx.com_image_thumbnail_05794198-474c-4ba5-90bd-d67364c4a20d_size_174_quality_85_52343a18daf729bbd64dfd533e56158977919565.jpg)
*Axial graphic of sella turcica, as viewed from above, depicts normal sellar and parasellar anatomy. Dura covering right cavernous sinus (CS) is removed to show CNV and CNVI. All cranial nerves are shown in left CS. Mandibular division of CNV does not run through CS but exits from Meckel cave inferiorly to enter foramen ovale. Note CS is not a single venous channel but is extensively septated.*
![Coronal graphic depicts contents of CSs. The following cranial nerves traverse CS within lateral wall of CS, from superior to inferior: Oculomotor (CNIII), trochlear (CNIV), 1st (ophthalmic or V1) and 2nd (maxillary or V2) divisions of trigeminal (CNV) nerves. The only cranial nerve actually within venous sinusoids of CS is abducens nerve (CNVI).](images/app.statdx.com_image_thumbnail_e9d6257a-a5ed-4f10-b6ed-7cfa7eb2c7c0_annotated_false_size_900_quality_90_27d8644d47e944f657aed471d4f6a1cdf20b4eb1.jpg)
*Coronal graphic depicts contents of CSs. The following cranial nerves traverse CS within lateral wall of CS, from superior to inferior: Oculomotor (CNIII), trochlear (CNIV), 1st (ophthalmic or V1) and 2nd (maxillary or V2) divisions of trigeminal (CNV) nerves. The only cranial nerve actually within venous sinusoids of CS is abducens nerve (CNVI).*
![Lateral graphic demonstrates cranial nerve detail in sellar region. CNIII, CNIV, CNV1, and CNV2 are in lateral dural wall of CS. CNVI courses within venous sinusoids of CS, adjacent to internal carotid artery (not shown). Meckel cave is CSF-filled, dural and arachnoid-lined invagination that communicates freely with prepontine cistern. It contains fascicles of trigeminal nerve (CNV) and trigeminal (gasserian) ganglion.](images/app.statdx.com_image_thumbnail_db00a42a-5144-4401-8f01-52f0bc69c5a1_annotated_false_size_900_quality_90_a9f186fed2eb9a50aece6d2a43f9b9e8ca29898b.jpg)
*Lateral graphic demonstrates cranial nerve detail in sellar region. CNIII, CNIV, CNV1, and CNV2 are in lateral dural wall of CS. CNVI courses within venous sinusoids of CS, adjacent to internal carotid artery (not shown). Meckel cave is CSF-filled, dural and arachnoid-lined invagination that communicates freely with prepontine cistern. It contains fascicles of trigeminal nerve (CNV) and trigeminal (gasserian) ganglion.*
### Axial T1 C+ MR
![Series of 6 axial contrast-enhanced T1 MR images, presented from inferior to superior through the skull base and CS, demonstrates the right maxillary nerve (V2) passing anteriorly into the foramen rotundum and the left trigeminal ganglion. The mandibular nerve (V3) will exit inferiorly through the foramen ovale (not shown).](images/app.statdx.com_image_thumbnail_23453f80-b0ac-4c3f-9561-54f3ac4e557b_annotated_false_size_900_quality_90_da10689d10c76d315f01d9a2199f4f90f00f005f.jpg)
*Series of 6 axial contrast-enhanced T1 MR images, presented from inferior to superior through the skull base and CS, demonstrates the right maxillary nerve (V2) passing anteriorly into the foramen rotundum and the left trigeminal ganglion. The mandibular nerve (V3) will exit inferiorly through the foramen ovale (not shown).*
![The Meckel cave is located posterior, inferior, and lateral relative to the CS. Dura forming the posterior part of the lateral wall of the CS also forms the upper medial 1/3 of the Meckel cave, separating the 2 structures. Note the abducens nerve (CNVI) seen here as a filling defect within the clival venous plexus, just before entering the Dorello canal.](images/app.statdx.com_image_thumbnail_c651a177-2d66-421d-8187-ed6ce0c0eed5_annotated_false_size_900_quality_90_b5d9a68b139586f4e111d6ee599a2d4fe5a319c1.jpg)
*The Meckel cave is located posterior, inferior, and lateral relative to the CS. Dura forming the posterior part of the lateral wall of the CS also forms the upper medial 1/3 of the Meckel cave, separating the 2 structures. Note the abducens nerve (CNVI) seen here as a filling defect within the clival venous plexus, just before entering the Dorello canal.*
![Both abducens nerves are seen coursing through the Dorello canal to enter the posterior CS. The right trigeminal nerve is seen entering the Meckel cave.](images/app.statdx.com_image_thumbnail_8746688b-78b8-4d15-97eb-ae5a32acda15_annotated_false_size_900_quality_90_0cc3ff9be5138d11ea18d6f2c40cfd9b981ba601.jpg)
*Both abducens nerves are seen coursing through the Dorello canal to enter the posterior CS. The right trigeminal nerve is seen entering the Meckel cave.*
![Cranial nerves exiting the CS through the superior orbital fissure (SOF) are CNIII, CNIV, CNVI, and the 1st (ophthalmic or V1) division of CNV.](images/app.statdx.com_image_thumbnail_1be8d75b-5223-465f-adc1-c218dadf8885_annotated_false_size_900_quality_90_a998531fa8db8a209b662f5db2500b38b9636e7b.jpg)
*Cranial nerves exiting the CS through the superior orbital fissure (SOF) are CNIII, CNIV, CNVI, and the 1st (ophthalmic or V1) division of CNV.*
![The optic nerve in the optic canal is located anteromedial to the anterior clinoid and superomedial to the SOF. It is separated from the SOF by a thin, bony strut, the &quot;optic strut.&quot; The cavernous carotid is posteromedial to the anterior clinoid. Note the origin of the ophthalmic artery from the internal carotid artery, just above the transition from the intracavernous carotid (below) to the intradural carotid (above) segments.](b7c9294d-48ae-43a8-b1c4-a70746cf4cb3)
*The optic nerve in the optic canal is located anteromedial to the anterior clinoid and superomedial to the SOF. It is separated from the SOF by a thin, bony strut, the &quot;optic strut.&quot; The cavernous carotid is posteromedial to the anterior clinoid. Note the origin of the ophthalmic artery from the internal carotid artery, just above the transition from the intracavernous carotid (below) to the intradural carotid (above) segments.*
![Pituitary infundibulum is seen within the suprasellar cistern posterior to the optic chiasm; avid enhancement seen here is typical. The supraclinoid internal carotid artery (or terminal segment) is seen laterally.](0596728f-68c6-442d-a9fe-893d9a05bcf5)
*Pituitary infundibulum is seen within the suprasellar cistern posterior to the optic chiasm; avid enhancement seen here is typical. The supraclinoid internal carotid artery (or terminal segment) is seen laterally.*
### Coronal T2 MR
![First of 6 sequential coronal T2 MR images, presented from posterior to anterior, demonstrates the optic tracts within the posterior aspect of the suprasellar cistern and the anterior cerebral and supraclinoid internal carotid arteries.](ed4e35f1-af99-49e8-a55a-4005b5b0ec1d)
*First of 6 sequential coronal T2 MR images, presented from posterior to anterior, demonstrates the optic tracts within the posterior aspect of the suprasellar cistern and the anterior cerebral and supraclinoid internal carotid arteries.*
![The posterior optic chiasm and part of the pituitary infundibulum are seen here. Note the internal carotid, middle cerebral, and anterior cerebral arteries. Individual trigeminal nerve rootlets are well demonstrated within the Meckel cave on thin-section imaging.](a3cfd543-67cb-4775-ba4e-f62241ad3566)
*The posterior optic chiasm and part of the pituitary infundibulum are seen here. Note the internal carotid, middle cerebral, and anterior cerebral arteries. Individual trigeminal nerve rootlets are well demonstrated within the Meckel cave on thin-section imaging.*
![Image at the level of the optic chiasm within the suprasellar cistern demonstrates normal pituitary gland and regional vascular anatomy. Note the normal location and appearance of the Meckel cave, seen inferior and lateral. The pituitary gland and venous blood within the CS are nearly isointense with each other on T2.](1545e00b-533b-41d5-a52e-8936ae75008b)
*Image at the level of the optic chiasm within the suprasellar cistern demonstrates normal pituitary gland and regional vascular anatomy. Note the normal location and appearance of the Meckel cave, seen inferior and lateral. The pituitary gland and venous blood within the CS are nearly isointense with each other on T2.*
![Normal appearances of the anterior pituitary gland, CS, Meckel cave, and suprasellar cistern are shown. The oculomotor nerves (CNIII) and optic nerves (CNII) are well seen. The anterior communicating artery, which connects the 2 anterior cerebral arteries and the left middle cerebral artery genu, are visible.](2a6c56a6-c63e-475a-a99a-9e4b7fd84e10)
*Normal appearances of the anterior pituitary gland, CS, Meckel cave, and suprasellar cistern are shown. The oculomotor nerves (CNIII) and optic nerves (CNII) are well seen. The anterior communicating artery, which connects the 2 anterior cerebral arteries and the left middle cerebral artery genu, are visible.*
![The most anterior aspect of the suprasellar cistern demonstrates normal optic nerves (CNII), oculomotor nerves (CNIII), cavernous internal carotid arteries, and the anterior cerebral artery within the anterior interhemispheric fissure.](51bb9fde-42a6-4915-8760-3e27cb2e558a)
*The most anterior aspect of the suprasellar cistern demonstrates normal optic nerves (CNII), oculomotor nerves (CNIII), cavernous internal carotid arteries, and the anterior cerebral artery within the anterior interhemispheric fissure.*
![The anterior clinoid processes seen here form the anterolateral boundaries of the sella turcica. Note the normal optic nerves, located medial to the anterior clinoids, and the anterior genu of the cavernous internal carotid artery on the left.](f2c9c67e-7fa4-4844-a456-8bc962930a90)
*The anterior clinoid processes seen here form the anterolateral boundaries of the sella turcica. Note the normal optic nerves, located medial to the anterior clinoids, and the anterior genu of the cavernous internal carotid artery on the left.*
### Coronal T1 C+ MR
![First of 6 sequential contrast-enhanced T1 MR images through the sella, presented from posterior to anterior, demonstrates details of the Meckel cave. The mandibular (V3) division of the trigeminal nerve is seen inferior to the normally enhancing gasserian ganglion.](01b3401d-b2a7-4824-962d-a414b059ae25)
*First of 6 sequential contrast-enhanced T1 MR images through the sella, presented from posterior to anterior, demonstrates details of the Meckel cave. The mandibular (V3) division of the trigeminal nerve is seen inferior to the normally enhancing gasserian ganglion.*
![The pituitary infundibulum insertion into the gland is well seen. Note the mandibular nerve (3rd division of trigeminal nerve or V3), best seen on the right as it exits through foramen ovale, entering the high masticator space. It is easy to see how extracranial tumors may gain access to the intracranial compartment without destroying the skull base, either through direct extension or via perineural spread.](3bba3f3e-d1f0-47b9-b129-9a705ead9bca)
*The pituitary infundibulum insertion into the gland is well seen. Note the mandibular nerve (3rd division of trigeminal nerve or V3), best seen on the right as it exits through foramen ovale, entering the high masticator space. It is easy to see how extracranial tumors may gain access to the intracranial compartment without destroying the skull base, either through direct extension or via perineural spread.*
![The left foramen ovale is well seen. Note the 3rd and 6th cranial nerves within the CS. All of the cranial nerves are not well seen on this image.](5fca60a5-326e-4257-89a8-6c18d0e62af2)
*The left foramen ovale is well seen. Note the 3rd and 6th cranial nerves within the CS. All of the cranial nerves are not well seen on this image.*
![This image demonstrates the oculomotor, abducens, and maxillary nerves. The pituitary gland enhances less strongly than venous blood in the CS.](525047f5-9d77-41df-9beb-0bfddae6d4bb)
*This image demonstrates the oculomotor, abducens, and maxillary nerves. The pituitary gland enhances less strongly than venous blood in the CS.*
![Normal cranial nerves traversing the CS from superior to inferior include the oculomotor nerve, trochlear nerve, abducens nerve, ophthalmic nerve (V1), and maxillary nerve (V2). The 4th cranial nerve (trochlear) is small and difficult to visualize but is normally located in the lateral CS between the oculomotor and trigeminal nerves, lateral to the abducens.](577a18fc-2b32-4a54-a7e3-8bf7d6b5fb46)
*Normal cranial nerves traversing the CS from superior to inferior include the oculomotor nerve, trochlear nerve, abducens nerve, ophthalmic nerve (V1), and maxillary nerve (V2). The 4th cranial nerve (trochlear) is small and difficult to visualize but is normally located in the lateral CS between the oculomotor and trigeminal nerves, lateral to the abducens.*
![The oculomotor nerve is again well seen in the anterior CS before it traverses the SOF. The vidian canal, which contains the vidian artery and nerve, is seen in the sphenoid bone. Note the optic nerves medial to the anterior clinoids before entering the optic canals.](18f67d99-bf37-4811-a300-6050a2dbabca)
*The oculomotor nerve is again well seen in the anterior CS before it traverses the SOF. The vidian canal, which contains the vidian artery and nerve, is seen in the sphenoid bone. Note the optic nerves medial to the anterior clinoids before entering the optic canals.*
### Anatomic-Pathologic Correlation
![Coronal T2 MR at the level of the CS demonstrates pituitary macroadenoma in the sella with suprasellar extension invading into the right CS. There is encasement of the right cavernous carotid with preserved flow void. There is significant mass effect on the optic apparatus. Note the normal left CS.](c348bc07-5a28-4da9-b1b4-a31c3699bb4f)
*Coronal T2 MR at the level of the CS demonstrates pituitary macroadenoma in the sella with suprasellar extension invading into the right CS. There is encasement of the right cavernous carotid with preserved flow void. There is significant mass effect on the optic apparatus. Note the normal left CS.*
![Axial MR performed in the same patient with bacterial sinusitis and bilateral CS thrombosis is shown. The flow voids in the internal carotid arteries are less distinct but present. The CS walls enhance normally, but the internal venous compartments of the CSs fail to enhance bilaterally due to venous sinus thrombosis.](755b6f42-cb4b-4bf6-8625-3684872dd8d1)
*Axial MR performed in the same patient with bacterial sinusitis and bilateral CS thrombosis is shown. The flow voids in the internal carotid arteries are less distinct but present. The CS walls enhance normally, but the internal venous compartments of the CSs fail to enhance bilaterally due to venous sinus thrombosis.*
![Axial 3D time-of-flight MRA demonstrates a saccular aneurysm arising from posterior genu of right cavernous carotid projecting medially with mild mass effect on the pituitary gland. Note normal left cavernous carotid flow-related signal.](ad6acd5b-4b46-4952-b5e3-34c89e93f697)
*Axial 3D time-of-flight MRA demonstrates a saccular aneurysm arising from posterior genu of right cavernous carotid projecting medially with mild mass effect on the pituitary gland. Note normal left cavernous carotid flow-related signal.*
### Additional Images
![Axial MR performed in the same patient with bacterial sinusitis and bilateral CS thrombosis is shown. The flow voids in the internal carotid arteries are less distinct but present. The CS walls enhance normally, but the internal venous compartments of the CSs fail to enhance bilaterally due to venous sinus thrombosis.](fe891366-4242-4aae-bed6-3d271b0757f8)
*Axial MR performed in the same patient with bacterial sinusitis and bilateral CS thrombosis is shown. The flow voids in the internal carotid arteries are less distinct but present. The CS walls enhance normally, but the internal venous compartments of the CSs fail to enhance bilaterally due to venous sinus thrombosis.*
![Bacterial sinusitis complicated by bilateral CS thrombosis is shown. Coronal MR through the CSs demonstrates complete opacification of the sphenoid sinus secondary to bacterial sinusitis. The lateral walls and roofs of the CSs enhance normally. However, there is conspicuous lack of enhancement in the central areas of CSs bilaterally. Normal flow voids (dark areas) are identified in the internal carotid arteries bilaterally.](a127685d-3d4a-49fb-be9c-31e42ce84375)
*Bacterial sinusitis complicated by bilateral CS thrombosis is shown. Coronal MR through the CSs demonstrates complete opacification of the sphenoid sinus secondary to bacterial sinusitis. The lateral walls and roofs of the CSs enhance normally. However, there is conspicuous lack of enhancement in the central areas of CSs bilaterally. Normal flow voids (dark areas) are identified in the internal carotid arteries bilaterally.*
![Lateral graphic of normal pituitary: The adenohypophysis is comprised of the pars tuberalis, pars intermedia, and pars distalis. The neurohypophysis is comprised of the median eminence of hypothalamus, infundibulum, and pars nervosa. Periosteal dural layer covers the sellar floor.](4cc94dad-d6eb-47a0-abe6-434ae4888f51)
*Lateral graphic of normal pituitary: The adenohypophysis is comprised of the pars tuberalis, pars intermedia, and pars distalis. The neurohypophysis is comprised of the median eminence of hypothalamus, infundibulum, and pars nervosa. Periosteal dural layer covers the sellar floor.*
![Axial CECT in a patient with bacterial facial cellulitis and bilateral CS thrombosis is shown. The superior ophthalmic veins show filling defects bilaterally, consistent with thrombosis. The lateral walls of the CSs enhance normally. However, on this delayed venous-phase image, the CSs demonstrate lack of significant internal enhancement consistent with bilateral thrombosis.](a460e7de-c988-4245-b02a-fc17d37838b9)
*Axial CECT in a patient with bacterial facial cellulitis and bilateral CS thrombosis is shown. The superior ophthalmic veins show filling defects bilaterally, consistent with thrombosis. The lateral walls of the CSs enhance normally. However, on this delayed venous-phase image, the CSs demonstrate lack of significant internal enhancement consistent with bilateral thrombosis.*
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---
title: "CNI (Olfactory Nerve)"
docid: "54c329dd-8363-4b61-9af3-bf78909ea790"
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pageDescription: "CNI (Olfactory Nerve)"
pageKeywords: "Head and Neck, Anatomy, Cranial Nerves, CNI (Olfactory Nerve)"
pageTitle: "CNI (Olfactory Nerve) | STATdx"
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---
## TERMINOLOGY
- ### Abbreviations
- Olfactory nerve (CNI)
- ### Synonyms
- 1st cranial nerve
- ### Definitions
- Visceral afferent cranial nerve for sense of smell
## IMAGING ANATOMY
- ### Overview
- Olfactory nerve segments
- Receptor neurons in olfactory epithelium in nasal vault
- Transethmoidal segment through cribriform plate
- Intracranial olfactory bulb, tract, and cortex
- ### Nasal Epithelium
- Pseudostratified columnar epithelium (~ 2 cm²), classically described in roof of each nasal cavity, adjacent septum, and lateral nasal cavity wall, including superior turbinates
- More extensive distribution up to middle turbinate, posterior and middle septum in recent studies
- Contains **b****ipolar olfactory receptor cells**
- Their peripheral processes/dendrites are sensory receptors for smell, each neuron expressing single type of odorant receptors out of ~ 400-500 types
- Olfactory glands (of Bowman) secrete mucous, which solubilizes inhaled scents (odorant molecules)
- ### Transethmoidal Segment
- Hundreds of central processes/axons of receptor cells are bundled into unmyelinated fascicles (fila olfactoria) interleaved with specialized glial cells called olfactory ensheathing cells
- **Fila olfactoria: Tr****ue** **olfactory nerves**
- ~ 20 fila traverse **cribriform plate** on each side of nasal cavity to synapse with olfactory bulb neurons
- ### Intracranial Olfactory Bulb and Tract
- Olfactory bulb and tracts: Extensions of brain, not nerves, but historically referred to as 1st cranial nerve
- **Olfactory bulb** (mean volume 125 ±17 mm³) closely apposed to cribriform plate at ventral surface of medial frontal lobe
- Histologically, bulb contains 6 concentric cell layers
- Axons within fila from receptor cells expressing same type of odorant receptor converge to spherical "glomerulus" in glomerular layer of bulb where they synapse with processes of secondary neurons (mitral and tufted cells) in deeper layers of bulb
- Short axon and granule cells modulate secondary neurons
- Axons of mitral and tufted cells coalesce to form lateral olfactory tract
- Recent studies have shown that main olfactory bulb is one of most prominent sites where intrinsic neurons are generated continuously after birth and in adulthood from cells located in subventricular zone of lateral ventricle
- **Olfactory tract** (mean length 28-30 mm) trifurcates to medial, intermediate, lateral striae at **anterior perforated substance**, where intermediate striae terminate
- This trifurcation creates **olfactory trigone**
- Anterior perforated substance is perforated by multiple small vascular structures
- Olfactory tract made up of **secondary sensory axons**, not primary sensory axons
- Majority of fibers project through lateral olfactory stria and intermediate stria
- Anterior olfactory nucleus formed by some neurons along olfactory tract
- Olfactory tubercle: Immediately behind division of olfactory stria, fused with anterior perforated substance
- ### Intracranial, Central Pathways
- Complex connections, incompletely elucidated in humans
- **Olfactory cortex**
- Cortical areas that receive input from olfactory bulb
- Composed of anatomically distinct areas: Piriform cortex, olfactory tubercle, anterior olfactory nucleus, anterior cortical nucleus of amygdala and periamygdaloid cortex, and anterior parts of entorhinal cortex
- **Lateral olfactory striae**
- Formed by majority of fibers of olfactory tracts
- Course over limen of insula to piriform (previously called prepiriform) cortex anterior to uncus and then to medial surface of amygdala
- 3-layered piriform cortex is phylogenetically older than typical 6-layer cortex
- Olfactory system is only sensory modality without thalamic relays
- On way to prepiriform area collaterals are given to subfrontal or frontal olfactory cortex
- Fibers also to subthalamic nuclei with collaterals/terminal fibers to thalamus and stria medullaris
- Projections from piriform cortex go to orbitofrontal cortex, thalamus (medial dorsal thalamic nucleus), hypothalamus, amygdala, and hippocampal formation
- **Medial olfactory striae**
- Majority terminate in parolfactory area of Broca (medial surface in front of subcallosal gyrus), some in subcallosal gyrus and anterior perforated substance
- Few fibers go contralaterally in anterior commissure
- **Medial forebrain bundle**
- Formed by fibers from basal olfactory region, periamygdaloid area, and septal nuclei
- Some fibers terminate in hypothalamic nuclei
- Most fibers go to autonomic areas in brainstem (reticular formation, salivatory nuclei, dorsal vagus nucleus)
- In human imaging studies, olfactory tubercle seen between uncus and medial forebrain bundle
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Olfactory dysfunction imaging depends on clinical context
- Sinus CT with coronal reconstructions typically done in post-URI anosmia, head trauma, or sinus surgery
- Brain and sinonasal MR used with suspected neurodegenerative disease (Alzheimer, Parkinson), neurologic symptoms, olfactory hallucinations, hypogonadism, or anosmia, especially post COVID-19
- ### Imaging Sweet Spots
- Intracranial: Include anterior cranial fossa floor and medial temporal lobes
- Extracranial: Include nasal vault and cribriform plate
- ### Imaging Pitfalls
- Coronal sinus CT includes nasal vault and cribriform plate but insensitive to intracranial pathology
- Remember to include medial temporal lobes in assessment
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- CNI dysfunction produces **unilateral** **anosmia**
- **Esthesioneuroblastoma** arises from olfactory epithelium
- Olfactory ensheathing cells can give rise to schwannomas
- Head trauma may cause anosmia: Cribriform plate fracture or shear forces; anterior temporal lobe injury
- Seizures involving olfactory network produce "uncinate fits" with olfactory hallucinations, variable oroglossal automatisms, and impaired awareness
- Olfactory bulb volumes decreased in head trauma, chronic rhinosinusitis, Alzheimer disease, multiple sclerosis, and schizophrenia
c13e9e32-1f8c-4d2a-a0df-b2db6628d93c
## Images
### Graphics
![Graphic of olfactory system viewed from below shows olfactory tracts coursing from olfactory bulbs to the olfactory trigone. In the olfactory trigone, fibers split up into lateral, intermediate, and medial striae. The majority of fibers course through the lateral stria to the piriform area and amygdala. Some fibers in the medial stria course through the anterior commissure to connect to the opposite tract. The majority of intermediate stria fibers terminate in the anterior perforated substance.](images/app.statdx.com_image_thumbnail_69f1284f-231a-474f-93f4-4927708dea0f_annotated_false_size_900_quality_90_6b758b82e7a9542ea9264b5c5912d7a49455844d.jpg)
*Graphic of olfactory system viewed from below shows olfactory tracts coursing from olfactory bulbs to the olfactory trigone. In the olfactory trigone, fibers split up into lateral, intermediate, and medial striae. The majority of fibers course through the lateral stria to the piriform area and amygdala. Some fibers in the medial stria course through the anterior commissure to connect to the opposite tract. The majority of intermediate stria fibers terminate in the anterior perforated substance.*
![Graphic of olfactory system viewed from below shows olfactory tracts coursing from olfactory bulbs to the olfactory trigone. In the olfactory trigone, fibers split up into lateral, intermediate, and medial striae. The majority of fibers course through the lateral stria to the piriform area and amygdala. Some fibers in the medial stria course through the anterior commissure to connect to the opposite tract. The majority of intermediate stria fibers terminate in the anterior perforated substance.](images/app.statdx.com_image_thumbnail_69f1284f-231a-474f-93f4-4927708dea0f_size_174_quality_85_3f1d414531945d7b2a25bb70a28185ccbc6ff70d.jpg)
*Graphic of olfactory system viewed from below shows olfactory tracts coursing from olfactory bulbs to the olfactory trigone. In the olfactory trigone, fibers split up into lateral, intermediate, and medial striae. The majority of fibers course through the lateral stria to the piriform area and amygdala. Some fibers in the medial stria course through the anterior commissure to connect to the opposite tract. The majority of intermediate stria fibers terminate in the anterior perforated substance.*
![Graphic of olfactory system viewed from below shows olfactory tracts coursing from olfactory bulbs to the olfactory trigone. In the olfactory trigone, fibers split up into lateral, intermediate, and medial striae. The majority of fibers course through the lateral stria to the piriform area and amygdala. Some fibers in the medial stria course through the anterior commissure to connect to the opposite tract. The majority of intermediate stria fibers terminate in the anterior perforated substance.](images/app.statdx.com_image_thumbnail_69f1284f-231a-474f-93f4-4927708dea0f_size_174_quality_85_449eedb7_20251018T124943Z.jpg)
*Graphic of olfactory system viewed from below shows olfactory tracts coursing from olfactory bulbs to the olfactory trigone. In the olfactory trigone, fibers split up into lateral, intermediate, and medial striae. The majority of fibers course through the lateral stria to the piriform area and amygdala. Some fibers in the medial stria course through the anterior commissure to connect to the opposite tract. The majority of intermediate stria fibers terminate in the anterior perforated substance.*
![Graphic of the olfactory system seen from an anterolateral oblique perspective shows central processes from bipolar olfactory cells in the olfactory epithelium crossing the cribriform plate, bundled as fila olfactoria (~ 20 per side) and connecting with secondary neurons in the olfactory bulbs. The olfactory trigone is visible dividing into lateral, intermediate, and medial striae.](images/app.statdx.com_image_thumbnail_b5a18f0e-1ff6-46f5-8ecd-ca4e16b3f0ce_annotated_false_size_900_quality_90_077d096b3261e446efc890974e618315294984dc.jpg)
*Graphic of the olfactory system seen from an anterolateral oblique perspective shows central processes from bipolar olfactory cells in the olfactory epithelium crossing the cribriform plate, bundled as fila olfactoria (~ 20 per side) and connecting with secondary neurons in the olfactory bulbs. The olfactory trigone is visible dividing into lateral, intermediate, and medial striae.*
### Coronal NECT
![First of 3 coronal bone CT images through the anterior cranial fossa are presented from posterior to anterior. The olfactory epithelium is found on the roof of the nasal cavity, extending inferolaterally on the superior turbinate and inferomedially on the nasal septum. The olfactory nerves pass through perforations in the cribriform plate. The olfactory bulbs sit just above the cribriform plates.](images/app.statdx.com_image_thumbnail_fe340ae1-e286-4cb9-b290-256f44b4d3b2_annotated_false_size_900_quality_90_4ceaed9a7e250585f10b138d4600891216abac0c.jpg)
*First of 3 coronal bone CT images through the anterior cranial fossa are presented from posterior to anterior. The olfactory epithelium is found on the roof of the nasal cavity, extending inferolaterally on the superior turbinate and inferomedially on the nasal septum. The olfactory nerves pass through perforations in the cribriform plate. The olfactory bulbs sit just above the cribriform plates.*
![In this CT, the ethmoid bone forms the medial floor of the anterior cranial fossa and consists of the cribriform plate and crista galli. The fenestrated cribriform plate is depressed relative to the orbital plate of the frontal bone. The fovea ethmoidalis is the most medial portion of the orbital plate of the frontal bone and separates the ethmoid labyrinth from the anterior cranial fossa.](images/app.statdx.com_image_thumbnail_6ba714b0-e7c7-4ac0-a4e3-8836660bb33a_annotated_false_size_900_quality_90_f134c9788fb2470becb6e661f03e4ff4fa1476b9.jpg)
*In this CT, the ethmoid bone forms the medial floor of the anterior cranial fossa and consists of the cribriform plate and crista galli. The fenestrated cribriform plate is depressed relative to the orbital plate of the frontal bone. The fovea ethmoidalis is the most medial portion of the orbital plate of the frontal bone and separates the ethmoid labyrinth from the anterior cranial fossa.*
![On this CT the anterior cribriform plate is seen at the base of the larger anterior crista galli.](images/app.statdx.com_image_thumbnail_2b618cc2-68b4-4a5a-9be9-2249ec4bae80_annotated_false_size_900_quality_90_8176b0151ab1ebd0c590ee0628ef40485adb2f98.jpg)
*On this CT the anterior cribriform plate is seen at the base of the larger anterior crista galli.*
### Coronal T2 MR
![First of 3 sequential coronal T2 MR images presented from posterior to anterior shows the triangular olfactory tracts, which are composed of centrally projecting axons, embedded within the olfactory sulcus.](images/app.statdx.com_image_thumbnail_44e8aced-9ae5-4e9d-9a15-0ce8c30f87df_annotated_false_size_900_quality_90_23a4469568353c063ad5d16281937b3df24142d5.jpg)
*First of 3 sequential coronal T2 MR images presented from posterior to anterior shows the triangular olfactory tracts, which are composed of centrally projecting axons, embedded within the olfactory sulcus.*
![The olfactory sulcus is easily identified separating the gyrus rectus medially from the orbital gyrus laterally. Again note the olfactory tracts at the base of the olfactory sulcus.](35e1c921-3cec-4bfa-9438-7e6abe01b7dd)
*The olfactory sulcus is easily identified separating the gyrus rectus medially from the orbital gyrus laterally. Again note the olfactory tracts at the base of the olfactory sulcus.*
![In this image through the anterior cribriform plate, note the olfactory bulbs. The olfactory bulbs are rostral enlargement of the olfactory tracts, which lie on either side of the midline on the intracranial surface of the cribriform plate. The olfactory nerves arise from the olfactory epithelium located in the roof nasal cavity and pass through the fenestrated cribriform plate to end in the olfactory bulbs.](e441bdc4-77de-4828-b247-2ce31cf06f3a)
*In this image through the anterior cribriform plate, note the olfactory bulbs. The olfactory bulbs are rostral enlargement of the olfactory tracts, which lie on either side of the midline on the intracranial surface of the cribriform plate. The olfactory nerves arise from the olfactory epithelium located in the roof nasal cavity and pass through the fenestrated cribriform plate to end in the olfactory bulbs.*
### Coronal T2
![Images from anterior to posterior demonstrate the configuration of the olfactory bulb as it transitions posteriorly to the olfactory tract.](b2cde5f4-9ff6-4f31-8ac7-646f450eee55)
*Images from anterior to posterior demonstrate the configuration of the olfactory bulb as it transitions posteriorly to the olfactory tract.*
![The olfactory bulb may demonstrate an oval or inverted J-shaped morphology.](82b1f925-4484-49ae-995c-f14844e15ed3)
*The olfactory bulb may demonstrate an oval or inverted J-shaped morphology.*
![The olfactory bulb's signal can be compared with the gyrus rectus to evaluate for any abnormal intensity.](db8abc6e-66d7-4b9f-8b7c-371f839a21fb)
*The olfactory bulb's signal can be compared with the gyrus rectus to evaluate for any abnormal intensity.*
### Flowchart: Olfactory Nerve Pathway
![This flowchart summarizes sequential structures in the olfactory nerve pathway beginning at the nasal epithelium to the initial areas of the cortex. Please refer to the text for further details regarding the cortex connections.](7553abd6-ee6a-43a2-b99c-dc1fa42c78b3)
*This flowchart summarizes sequential structures in the olfactory nerve pathway beginning at the nasal epithelium to the initial areas of the cortex. Please refer to the text for further details regarding the cortex connections.*
docs_md/articles/cnii-optic-nerve_1b5322bb-bdca-4605-9ab5-43598b5c322f.md
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title: "CNII (Optic Nerve)"
docid: "1b5322bb-bdca-4605-9ab5-43598b5c322f"
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- key: "94f835c8-fa13-4e8a-995b-53048e6b0605"
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pageDescription: "CNII (Optic Nerve)"
pageKeywords: "Head and Neck, Anatomy, Cranial Nerves, CNII (Optic Nerve)"
pageTitle: "CNII (Optic Nerve) | STATdx"
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---
## TERMINOLOGY
- ### Abbreviations
- Cranial nerve II (CNII)
- ### Synonyms
- 2nd cranial nerve
- ### Definitions
- CNII: Nerve of sight
- Visual pathway consists of optic nerve, optic chiasm, and retrochiasmal structures
## IMAGING ANATOMY
- ### Overview
- Optic nerve **not** true cranial nerve but rather **extension of brain**
- Represents collection of retinal ganglion cell axons
- Myelinated by **oligodendrocytes** not by Schwann cells as with true cranial nerves
- Enclosed by meninges
- Throughout its course to visual cortex, nerve fibers are arranged in **retinotopic order**
- Optic nerve has 4 segments
- Intraocular, intraorbital, intracanalicular, and intracranial
- Partial decussation of CNII fibers within optic chiasm
- Axons from medial portion of each retina cross to join those from lateral portion of opposite retina
- Retrochiasmal structures: Optic tract, lateral geniculate body, optic radiation, and visual cortex
- ### Optic Pathway
- **Optic nerve**: **Intraocular****segment**
- 1 mm in length
- Region of sclera termed **lamina cribrosa** where ganglion cell axons exit globe
- **Optic nerve**: **Intraorbital segment**
- 20-30 mm in length
- Extends posteromedially & superiorly from back of globe to orbital apex within intraconal space of orbit
- Tortuous course allowing for movements of eye
- Covered by same 3 meningeal layers as brain
- Outer dura, middle arachnoid, and inner pia
- Subarachnoid space (SAS) between arachnoid and pia contains CSF; continuous with SAS of suprasellar cistern
- Fluctuations in intracranial pressure transmitted via SAS of optic nerve-sheath complex
- Central retinal artery
- 1st branch of ophthalmic artery
- Enters optic nerve halfway along intraorbital segment
- **Optic nerve**: **Intracanalicular s****egment**
- ~ 10-mm segment within bony optic canal
- Ophthalmic artery lies inferolateral to CNII
- Dura of CNII fuses with orbit periosteum (periorbita)
- Weakest point of anterior orbital pathway as it is fixed to bony canal
- **Optic nerve**: **Intracranial segment**
- ~ 10 mm in length from optic canal to chiasm
- Surrounded by optic sheath and dorsal surface covered by falciform ligament
- Ophthalmic artery runs inferolateral to nerve
- **Optic chiasm**
- Horizontally oriented; X-shaped structure within suprasellar cistern
- Forms part of floor of 3rd ventricle between optic recess anteriorly and infundibular recess posteriorly
- Positioned over diaphragma sellae (normofixed) or tuberculum sellae (prefixed) or dorsum sellae (postfixed)
- Anteriorly, chiasm divides into optic nerves
- Axons representing temporal visual fields decussate in chiasm
- Posteriorly, chiasm divides into optic tracts
- Medial fibers of optic tracts cross in chiasm to connect lateral geniculate bodies of both sides (commissure of Gudden)
- **Optic tracts**
- Posterior extension of optic chiasm
- Fibers pass posterolaterally, curving around cerebral peduncle, and divide into medial and lateral bands
- Lateral band (majority of fibers) ends in **lateral geniculate body** of thalamus
- Medial band goes by medial geniculate body to pretectal nuclei deep to superior colliculi
- **Optic radiation****and****visual cortex**
- Axons from lateral geniculate body form **optic radiations** (geniculocalcarine tracts)
- Fan out from lateral geniculate body and run as broad fiber tract to calcarine fissure
- Initially pass laterally behind posterior limb internal capsule and basal ganglia
- Extend posteriorly around lateral ventricle passing through posterior temporal and parietal lobes
- Terminate in calcarine cortex (primary visual cortex) on medial surface of occipital lobes
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- CT best for skull base and optic canal bony anatomy
- MR for CNII, optic chiasm, and retrochiasmal structures
- Axial and coronal thin-section T2, T1, and T1 C+ images
- ### Imaging Pitfalls
- Orbital CT may see subtle calcified optic sheath meningioma when MR may not
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Lesion location
- Optic nerve pathology: **Monocular****visual loss**
- Central optic chiasm pathology: **Bitemporal heteronymous hemianopsia**
- Peripheral optic chiasm pathology: **Ipsilateral nasal hemianopsia**
- Retrochiasmal pathology: **Homonymous hemianopsia**
- Increased intracranial pressure transmitted along SAS of optic nerve-sheath complex presenting as papilledema
- Imaging demonstrates flattening of posterior sclera, tortuosity and elongation of intraorbital optic nerves, and dilatation of perioptic SAS
dc1cc4da-1f51-43d0-b40e-b0c63f7484fa
## Images
### Graphics
![Axial graphic through the visual pathway shows medial retinal fibers crossing in the optic chiasm so that fibers from the left 1/2 of both retinas course in the left optic tract, and fibers in the right 1/2 of both retinas course in the right optic tract (purple and green, respectively). The majority of retinal nerve fibers terminate in the lateral geniculate bodies, where synaptic neuronal cell bodies give rise to optic radiations, which extend to the visual cortices. A few retinal nerve fibers (blue) involved in optic reflexes bypass the lateral geniculate bodies and terminate in the pretectal nuclei. Medial fibers of optic tracts cross in chiasm to connect lateral geniculate bodies of both sides (yellow).](images/app.statdx.com_image_thumbnail_0e752ebe-6329-44e4-bb69-8a49ebfab053_annotated_false_size_900_quality_90_f8e678306ce44395edb3023b30f6a4d0749ed85f.jpg)
*Axial graphic through the visual pathway shows medial retinal fibers crossing in the optic chiasm so that fibers from the left 1/2 of both retinas course in the left optic tract, and fibers in the right 1/2 of both retinas course in the right optic tract (purple and green, respectively). The majority of retinal nerve fibers terminate in the lateral geniculate bodies, where synaptic neuronal cell bodies give rise to optic radiations, which extend to the visual cortices. A few retinal nerve fibers (blue) involved in optic reflexes bypass the lateral geniculate bodies and terminate in the pretectal nuclei. Medial fibers of optic tracts cross in chiasm to connect lateral geniculate bodies of both sides (yellow).*
![Axial graphic through the visual pathway shows medial retinal fibers crossing in the optic chiasm so that fibers from the left 1/2 of both retinas course in the left optic tract, and fibers in the right 1/2 of both retinas course in the right optic tract (purple and green, respectively). The majority of retinal nerve fibers terminate in the lateral geniculate bodies, where synaptic neuronal cell bodies give rise to optic radiations, which extend to the visual cortices. A few retinal nerve fibers (blue) involved in optic reflexes bypass the lateral geniculate bodies and terminate in the pretectal nuclei. Medial fibers of optic tracts cross in chiasm to connect lateral geniculate bodies of both sides (yellow).](images/app.statdx.com_image_thumbnail_0e752ebe-6329-44e4-bb69-8a49ebfab053_size_174_quality_85_a26053d5027eb770019396717c478c9aedbf311b.jpg)
*Axial graphic through the visual pathway shows medial retinal fibers crossing in the optic chiasm so that fibers from the left 1/2 of both retinas course in the left optic tract, and fibers in the right 1/2 of both retinas course in the right optic tract (purple and green, respectively). The majority of retinal nerve fibers terminate in the lateral geniculate bodies, where synaptic neuronal cell bodies give rise to optic radiations, which extend to the visual cortices. A few retinal nerve fibers (blue) involved in optic reflexes bypass the lateral geniculate bodies and terminate in the pretectal nuclei. Medial fibers of optic tracts cross in chiasm to connect lateral geniculate bodies of both sides (yellow).*
![Axial graphic of the orbit shows the 4 segments of the optic nerve (intraocular, intraorbital, intracanalicular, and intracranial). At the annulus of Zinn, the dural sheath of the intraorbital segment becomes contiguous with periorbita.](images/app.statdx.com_image_thumbnail_65156421-6d1d-4b90-a0e9-406c9ac44cd2_annotated_false_size_900_quality_90_dd78b77fa3c80ad048d4bb067e600f6d290adde8.jpg)
*Axial graphic of the orbit shows the 4 segments of the optic nerve (intraocular, intraorbital, intracanalicular, and intracranial). At the annulus of Zinn, the dural sheath of the intraorbital segment becomes contiguous with periorbita.*
![Sagittal graphic through the orbit shows continuity of the dural sheath of the intraorbital segment of CNII with the sclera. At the annulus of Zinn, the dural sheath is continuous with the periorbita (not seen in this graphic). The central retinal artery and vein enter the midintraorbital segment of CNII to supply the retina.](images/app.statdx.com_image_thumbnail_8f6b26f0-2da2-45eb-b4a5-53a4e0e47156_annotated_false_size_900_quality_90_6b4d1e9eedc91e70301c48ebb33b2293516af4fd.jpg)
*Sagittal graphic through the orbit shows continuity of the dural sheath of the intraorbital segment of CNII with the sclera. At the annulus of Zinn, the dural sheath is continuous with the periorbita (not seen in this graphic). The central retinal artery and vein enter the midintraorbital segment of CNII to supply the retina.*
![Coronal graphic through the distal optic nerve shows encasement of the optic nerve by the arachnoid and dura. The subarachnoid space of CNII is continuous with the cerebral subarachnoid space. The central retinal artery and vein pierce the dura of the distal intraorbital segment and continue to the retina in the center of CNII.](images/app.statdx.com_image_thumbnail_6dcfa4a2-f53b-46f9-a6a8-a6fa7b12ffa6_annotated_false_size_900_quality_90_a27770e89795aa17e0404ca7efbd43e1d8464798.jpg)
*Coronal graphic through the distal optic nerve shows encasement of the optic nerve by the arachnoid and dura. The subarachnoid space of CNII is continuous with the cerebral subarachnoid space. The central retinal artery and vein pierce the dura of the distal intraorbital segment and continue to the retina in the center of CNII.*
### Axial T2 FS MR
![Axial T2 FS MR through the orbits shows normal-appearing optic discs, intraorbital &amp; intracanalicular segments of optic nerves. The intraocular segments are poorly delineated on this fat-saturated image. Note the thin sleeve of CSF-filled subarachnoid space surrounding the optic nerves. The outer dural covering of the optic nerve sheath merges with sclera anteriorly and posteriorly as periorbita at the annulus of Zinn.](images/app.statdx.com_image_thumbnail_91ce8bc5-f758-4b77-a2b1-7422eabcf94d_annotated_false_size_900_quality_90_9890862b45824a211e192ec66ab6b84cec115599.jpg)
*Axial T2 FS MR through the orbits shows normal-appearing optic discs, intraorbital &amp; intracanalicular segments of optic nerves. The intraocular segments are poorly delineated on this fat-saturated image. Note the thin sleeve of CSF-filled subarachnoid space surrounding the optic nerves. The outer dural covering of the optic nerve sheath merges with sclera anteriorly and posteriorly as periorbita at the annulus of Zinn.*
![Axial T2 FS MR shows the intracranial segments of both optic nerves joining to form the optic chiasm in the suprasellar cistern. The optic chiasm is usually located over the diaphragma sella (normofixed) or, rarely, over the tuberculum sella (prefixed) or dorsum sella (post fixed).](images/app.statdx.com_image_thumbnail_12ffa800-43fc-4d14-8a55-cfb1542adb0a_annotated_false_size_900_quality_90_8663b89173d20fc350a2e3126665e2a26383f0b5.jpg)
*Axial T2 FS MR shows the intracranial segments of both optic nerves joining to form the optic chiasm in the suprasellar cistern. The optic chiasm is usually located over the diaphragma sella (normofixed) or, rarely, over the tuberculum sella (prefixed) or dorsum sella (post fixed).*
![Axial T2 FS MR shows bilateral optic tracts coursing posteriorly and laterally curving around the cerebral peduncles. The lateral band of fibers terminates in the lateral geniculate body, and the medial band terminates in the pretectal nuclei via the medial geniculate body. Pretectal nuclei are located deep to superior colliculi in the dorsal midbrain.](540d9231-6ce7-408b-be32-23b5064f4fe4)
*Axial T2 FS MR shows bilateral optic tracts coursing posteriorly and laterally curving around the cerebral peduncles. The lateral band of fibers terminates in the lateral geniculate body, and the medial band terminates in the pretectal nuclei via the medial geniculate body. Pretectal nuclei are located deep to superior colliculi in the dorsal midbrain.*
### Coronal T2 FS MR
![Coronal T2 FS MR shows normal intraorbital segments of the bilateral optic nerves. A thin sleeve of CSF surrounds the optic nerves. Note that the optic nerve signal matches that of white matter.](43474f49-959b-4774-aa3c-6d98cf69bdb9)
*Coronal T2 FS MR shows normal intraorbital segments of the bilateral optic nerves. A thin sleeve of CSF surrounds the optic nerves. Note that the optic nerve signal matches that of white matter.*
![Coronal T2 FS MR shows intracanalicular segments of the bilateral optic nerves. They usually measure between 4-9 mm. The ophthalmic artery is located inferior to CNII in the optic nerve canal (not depicted). Dura covering the optic nerve fuses with periorbita in the optic nerve canal.](526efe80-bf50-4eff-bed7-1bed62739173)
*Coronal T2 FS MR shows intracanalicular segments of the bilateral optic nerves. They usually measure between 4-9 mm. The ophthalmic artery is located inferior to CNII in the optic nerve canal (not depicted). Dura covering the optic nerve fuses with periorbita in the optic nerve canal.*
![Coronal T2 FS MR shows intracranial segments of the bilateral optic nerves coursing posteriorly and medially. They are covered by pia and arachnoid membranes. The ophthalmic artery usually runs inferolateral to the nerves.](71e4a794-a8e8-4932-8f47-0474ee9b81b9)
*Coronal T2 FS MR shows intracranial segments of the bilateral optic nerves coursing posteriorly and medially. They are covered by pia and arachnoid membranes. The ophthalmic artery usually runs inferolateral to the nerves.*
![Coronal T2 FS MR shows the horizontally oriented optic chiasm in the suprasellar cistern. It is usually located above the diaphragma sellae (normofixed). Fibers from the medial 1/2 of both retina cross over to the opposite side in the chiasm. Medial fibers in the optic tracts cross over to the opposite side at the chiasm to connect both lateral geniculate bodies (commissure of Gudden).](07aae4da-df2b-48ca-a118-262273fcc289)
*Coronal T2 FS MR shows the horizontally oriented optic chiasm in the suprasellar cistern. It is usually located above the diaphragma sellae (normofixed). Fibers from the medial 1/2 of both retina cross over to the opposite side in the chiasm. Medial fibers in the optic tracts cross over to the opposite side at the chiasm to connect both lateral geniculate bodies (commissure of Gudden).*
![Coronal T2 FS MR through the posterior part of the optic chiasm shows the chiasm dividing into optic tracts. Note the optic chiasm forming part of the floor of the 3rd ventricle. The optic chiasm is closely associated with the pituitary infundibulum.](15e6b617-6433-43d3-adb2-58dd46524b00)
*Coronal T2 FS MR through the posterior part of the optic chiasm shows the chiasm dividing into optic tracts. Note the optic chiasm forming part of the floor of the 3rd ventricle. The optic chiasm is closely associated with the pituitary infundibulum.*
![Coronal T2 FS MR shows the bilateral optic tracts coursing posteriorly and laterally around the cerebral peduncles (not shown). The optic tracts divide into medial and lateral bands. The medial band ends in the pretectal nuclei via the medial geniculate bodies, and the lateral band ends in the lateral geniculate bodies. Note the pretectal nuclei are located deep to the superior colliculi in the dorsal midbrain (not shown).](16c3fedf-bb60-4629-a935-ad793c79facc)
*Coronal T2 FS MR shows the bilateral optic tracts coursing posteriorly and laterally around the cerebral peduncles (not shown). The optic tracts divide into medial and lateral bands. The medial band ends in the pretectal nuclei via the medial geniculate bodies, and the lateral band ends in the lateral geniculate bodies. Note the pretectal nuclei are located deep to the superior colliculi in the dorsal midbrain (not shown).*
### Sagittal & Coronal T1 MR
![Sagittal T1 MR through the optic nerve demonstrates the intraorbital segment of the optic nerve. The sclera of the globe is hypointense, while the pigmented choroid of the uvea is hyperintense due to T1-shortening effects of melanin.](f5ac88c6-53aa-480c-b064-6238c9f6b2ff)
*Sagittal T1 MR through the optic nerve demonstrates the intraorbital segment of the optic nerve. The sclera of the globe is hypointense, while the pigmented choroid of the uvea is hyperintense due to T1-shortening effects of melanin.*
![First of 2 coronal T1 MR images through the orbit from posterior to anterior is shown. This section through the orbital apex shows the optic nerve passing through the common annular tendon, which serves as the site of origin of the rectus muscles.](2c4f154b-b89e-4e96-8653-9dd71a47239f)
*First of 2 coronal T1 MR images through the orbit from posterior to anterior is shown. This section through the orbital apex shows the optic nerve passing through the common annular tendon, which serves as the site of origin of the rectus muscles.*
![In this image, both the superolateral ophthalmic vein and the superomedial ophthalmic artery are visible. Note that the subarachnoid space is visible as a thin, black line surrounding the optic nerve, a finding often not seen on routine T1 imaging of the orbit.](4f9f69a7-597c-4334-ae42-4ab08e6ee44b)
*In this image, both the superolateral ophthalmic vein and the superomedial ophthalmic artery are visible. Note that the subarachnoid space is visible as a thin, black line surrounding the optic nerve, a finding often not seen on routine T1 imaging of the orbit.*
### Optic Nerve Pathology
![Graphic of the optic pathway shows lesions at various levels and resultant visual field defects. The lesions are depicted at the level of the (1) optic nerve, (2) central optic chiasm, (3) peripheral optic chiasm, (4) optic tract, and (5) optic radiations.](b6276482-b4e1-4944-ad6c-95d7c33321b9)
*Graphic of the optic pathway shows lesions at various levels and resultant visual field defects. The lesions are depicted at the level of the (1) optic nerve, (2) central optic chiasm, (3) peripheral optic chiasm, (4) optic tract, and (5) optic radiations.*
![Coronal T1 C+ FS MR of the orbit in a patient with right eye vision loss show eccentric nodular thickening of the right optic nerve sheath with the optic nerve displaced and compressed inferomedially, suggesting optic nerve sheath meningioma.](aa79def6-44c2-4a6d-8043-f0debb44c48d)
*Coronal T1 C+ FS MR of the orbit in a patient with right eye vision loss show eccentric nodular thickening of the right optic nerve sheath with the optic nerve displaced and compressed inferomedially, suggesting optic nerve sheath meningioma.*
![Coronal T1 MR through the sella in a patient with bitemporal hemianopia demonstrates a large pituitary macroadenoma with mass effect on the optic chiasm, which appears to be displaced superiorly and stretched over the tumor.](8cbe5479-f53a-4e7c-a21f-abec8aa05951)
*Coronal T1 MR through the sella in a patient with bitemporal hemianopia demonstrates a large pituitary macroadenoma with mass effect on the optic chiasm, which appears to be displaced superiorly and stretched over the tumor.*
### Additional Images
![In this image just behind the globe, all the extraocular muscles are clearly visible. The levator palpebrae superioris muscle may be difficult to distinguish from the superior rectus muscle even with high-resolution MR imaging.](280ae045-bbe4-43dc-baa4-ebc5cb337a6a)
*In this image just behind the globe, all the extraocular muscles are clearly visible. The levator palpebrae superioris muscle may be difficult to distinguish from the superior rectus muscle even with high-resolution MR imaging.*
![Axial T1 MR demonstrates the intraorbital segment of the optic nerve extending posteromedially from the back of the globe to the orbital apex, surrounded by fat within the intraconal space. Note the intracanalicular segment passing through the bony optic canal.](87bfc5cd-4e3e-4b50-a945-b2f265d3660f)
*Axial T1 MR demonstrates the intraorbital segment of the optic nerve extending posteromedially from the back of the globe to the orbital apex, surrounded by fat within the intraconal space. Note the intracanalicular segment passing through the bony optic canal.*
![Axial T1 MR shows the origin of the optic nerve from the globe. Nerve fibers of the retina unite, forming the optic nerve before exiting the eyeball through the lamina cribrosa, a thin, perforated portion of the sclera. In the superior orbit, the lacrimal gland is seen in its superolateral fossa.](e79408c6-88de-413d-a31b-581f34efbd5f)
*Axial T1 MR shows the origin of the optic nerve from the globe. Nerve fibers of the retina unite, forming the optic nerve before exiting the eyeball through the lamina cribrosa, a thin, perforated portion of the sclera. In the superior orbit, the lacrimal gland is seen in its superolateral fossa.*
![First of 3 axial STIR MR images from inferior to superior demonstrate intraorbital, intracanalicular, and intracranial segments of the optic nerve. Intraorbital segment extends from the back of the globe posteromedially to the orbital apex within the intraconal space. Intracanalicular segment passes through the bony optic canal. Intracranial segment is ~ 10 mm long from optic canal to chiasm.](e9c5041a-956a-4ac6-b80a-4ba428319824)
*First of 3 axial STIR MR images from inferior to superior demonstrate intraorbital, intracanalicular, and intracranial segments of the optic nerve. Intraorbital segment extends from the back of the globe posteromedially to the orbital apex within the intraconal space. Intracanalicular segment passes through the bony optic canal. Intracranial segment is ~ 10 mm long from optic canal to chiasm.*
![Subarachnoid space with cerebrospinal fluid surrounds the optic nerve and is continuous with the subarachnoid space of the suprasellar cistern. Optic chiasm lies within the suprasellar cistern. Optic tracts extend posteriorly around the cerebral peduncles to the lateral geniculate body.](dfd2605b-6457-40a0-baa4-02a34cd8c443)
*Subarachnoid space with cerebrospinal fluid surrounds the optic nerve and is continuous with the subarachnoid space of the suprasellar cistern. Optic chiasm lies within the suprasellar cistern. Optic tracts extend posteriorly around the cerebral peduncles to the lateral geniculate body.*
![Majority of fibers from optic tracts terminate in the lateral geniculate body located at the posteroinferior aspect of the thalamus. Efferent axons from lateral geniculate body form optic radiation extending to the calcarine cortex.](8db404c6-8241-49e8-a2fa-7981af1290c8)
*Majority of fibers from optic tracts terminate in the lateral geniculate body located at the posteroinferior aspect of the thalamus. Efferent axons from lateral geniculate body form optic radiation extending to the calcarine cortex.*
![First of 6 coronal T2 MR images shows the optic tracts and chiasm from posterior to anterior. The optic tracts course posterolaterally, curving around the cerebral peduncle to eventually terminate in lateral geniculate body (lateral root) and pretectal nuclei at the superior colliculi (medial band).](df21e0a3-abe2-49b1-ab3b-9e56c5d8d865)
*First of 6 coronal T2 MR images shows the optic tracts and chiasm from posterior to anterior. The optic tracts course posterolaterally, curving around the cerebral peduncle to eventually terminate in lateral geniculate body (lateral root) and pretectal nuclei at the superior colliculi (medial band).*
![Optic tracts course through the posterior suprasellar cistern toward the ambient cistern, closely related to basal vein (of Rosenthal).](e9d6942a-c2e9-412c-9f3e-4eab4e739c07)
*Optic tracts course through the posterior suprasellar cistern toward the ambient cistern, closely related to basal vein (of Rosenthal).*
![In this image through the back of the optic chiasm, the optic tracts are shown as the posterior extension of the optic chiasm carrying fibers from the ipsilateral 1/2 of both retinae. The tuber cinereum leads to the infundibulum (pituitary stalk). Notice the 3rd ventricle just above the posterior optic chiasm.](c3e930bf-21ab-42f4-9f73-6c47f342321d)
*In this image through the back of the optic chiasm, the optic tracts are shown as the posterior extension of the optic chiasm carrying fibers from the ipsilateral 1/2 of both retinae. The tuber cinereum leads to the infundibulum (pituitary stalk). Notice the 3rd ventricle just above the posterior optic chiasm.*
![In this image, the optic chiasm is seen forming part of the floor of the 3rd ventricle between the optic recess anteriorly and the infundibular recess posteriorly. It is immediately anterior to the infundibulum (pituitary stalk).](3ca1fb8c-dd22-409f-832f-638cb7c972ec)
*In this image, the optic chiasm is seen forming part of the floor of the 3rd ventricle between the optic recess anteriorly and the infundibular recess posteriorly. It is immediately anterior to the infundibulum (pituitary stalk).*
![The optic chiasm is a horizontally oriented, X-shaped structure within the suprasellar cistern. Nerve fibers from the medial halves of both retinae cross to continue to lateral geniculate bodies. Interruption of crossing chiasmatic fibers leads to bitemporal hemianopia.](000c6ecf-5b84-4792-a9ad-a91036d613d2)
*The optic chiasm is a horizontally oriented, X-shaped structure within the suprasellar cistern. Nerve fibers from the medial halves of both retinae cross to continue to lateral geniculate bodies. Interruption of crossing chiasmatic fibers leads to bitemporal hemianopia.*
![The intracranial segment of the optic nerves are visible in this image. This segment is ~ 10 mm in length from the optic canal anteriorly to the optic chiasm posteriorly. The nerves are covered by pia at this point. The bright CSF within the suprasellar cistern surrounds the nerves.](d84d0914-f4bd-4b29-a563-9d44d03448f0)
*The intracranial segment of the optic nerves are visible in this image. This segment is ~ 10 mm in length from the optic canal anteriorly to the optic chiasm posteriorly. The nerves are covered by pia at this point. The bright CSF within the suprasellar cistern surrounds the nerves.*
docs_md/articles/cniii-oculomotor-nerve_ad21daaf-1f28-4f9c-bc74-3d0142c167ab.md
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---
title: "CNIII (Oculomotor Nerve)"
docid: "ad21daaf-1f28-4f9c-bc74-3d0142c167ab"
authors:
- key: "1fa14dfd-71ea-4960-908e-e720313bc63a"
value: "Santhosh Gaddikeri, MD"
- key: "94f835c8-fa13-4e8a-995b-53048e6b0605"
value: "Philip R. Chapman, MD"
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name: "Cranial Nerves"
slug: "cranial-nerves"
treeNodeId: "bc7da3a0-2ad7-4f30-949a-0db0d1e6f620"
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name: "CNIII (Oculomotor Nerve) "
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lastUpdated: "01/29/24"
pageDescription: "CNIII (Oculomotor Nerve)"
pageKeywords: "Head and Neck, Anatomy, Cranial Nerves, CNIII (Oculomotor Nerve) "
pageTitle: "CNIII (Oculomotor Nerve) | STATdx"
enhancedTitle: "CNIII (Oculomotor Nerve)"
type: "ANATOMY"
breadcrumbs:
- "Head and Neck"
- "Anatomy"
- "Cranial Nerves"
- "CNIII (Oculomotor Nerve) "
---
## TERMINOLOGY
- ### Abbreviations
- Oculomotor nerve (CNIII, CN3)
- Oculomotor nuclear complex (ONC)
- Extraocular muscle (EOM)
- Medial longitudinal fasciculus (MLF)
- Edinger-Westphal nucleus (EWn)
- Superior orbital fissure (SOF)
- ### Synonyms
- 3rd cranial nerve
- ### Definitions
- CNIII: Motor nerve to EOMs except lateral rectus (CNVI) and superior oblique muscles (CNIV); parasympathetic motor to pupillary sphincter and ciliary muscle
## IMAGING ANATOMY
- ### Overview
- Purely motor cranial nerve with general somatic efferent fibers as well as general visceral efferent (parasympathetic)
- Supplies all EOMs except superior oblique and lateral rectus muscles via general somatic efferent innervation
- Innervates pupillary sphincter and ciliary muscles via parasympathetic innervation
- Originates from ONC in posterior midbrain
- Can be divided into 7 segments: Intramesencephalic, interpeduncular cisternal, petroclinoid, trigonal, cavernous, fissural, and orbital
- ### Oculomotor Nerve Complex
- There are paired paramedian ONCs located in posterior aspect of midbrain at level of superior colliculus
- Partially embedded in periaqueductal gray matter anterior (ventral) to cerebral aqueduct
- ONC has complex cytoarchitecture with multiple motor nuclei and parasympathetic nucleus
- Contains motor neurons of medial, inferior, and superior recti, inferior oblique, and levator palpebrae muscles
- Motor neurons are arranged into subgroups generally referred to as nuclei
- Motor nuclei are arranged in 2 paramedian clusters or stacks referred to as columns or somatic columns
- Each paramedian somatic column consists of 4 relatively distinct nuclei, providing axons to EOMs
- **Ventral nucleus**: Ipsilateral medial rectus
- **Central nucleus**: Contralateral superior rectus and ipsilateral inferior oblique
- **Dorsolateral nucleus**: Ipsilateral medial rectus
- **Dorsomedial nuclei**: Ipsilateral inferior rectus
- Just inferior to paired columns is single midline motor nucleus, **central caudal nucleus**
- Central caudal nucleus contains motor neurons for levator palpebrae muscle, possibly provides crossed and uncrossed axons
- **EWn**
- More complex than classically considered
- Anatomy is confounded by differences in primates and humans
- Afferent inputs primarily from bilateral pretectal nuclei mediating pupillary light reflex and from visual cortex mediating accommodation
- Efferent fibers travel in CNIII and in MLF
- Nomenclature confusing given inconsistent application of term EWn to 2 different groups of neurons that contain different cell types and provide different function
- 1st group: Preganglionic parasympathetic component (EWpg)
- 2nd group: Nonpreganglionic centrally projecting component (EWcp)
- **EWnp** (parasympathetic component)
- Provides parasympathetic motor to pupillary sphincter and ciliary muscles of eye
- In humans, preganglionic parasympathetic neurons are located posteromedial to somatic columns near midline but do not form compact or distinct nucleus
- **EWncp** (centrally projecting components)
- Located posteromedial to somatic columns, in between columns and parasympathetic neurons of EWpg
- Forms compact and distinct nucleus
- Consists of peptidergic neurons that project to brainstem, spinal cord, and prosencephalic regions
- Not definitely related to ocular function; may function in feeding behavior, stress responses, addiction, and pain
- **MLF**
- Main intersegmental tract of brainstem
- Small paramedian tract coursing from upper cervical cord to interstitial nucleus of Cajal (lateral wall of 3rd ventricle)
- Interconnects oculomotor, trochlear, abducens, EWn, vestibular, reticular, and spinal accessory nuclei
- Coordinates conjugate eye movements with associated movements of head and neck
- Lesions of MLF result in internuclear ophthalmoplegia (INO)
- **Nucleus of Perlia**
- Small linear nucleus medial to main motor nuclei near midline of midbrain
- Function less clear; may function in ocular convergence
- May provide some motor fibers to superior rectus
- Arterial supply to ONC and intramesencephalic nerves via group of small penetrating arteries that arise from terminal regions of basilar artery near origins of superior cerebellar and posterior cerebral arteries
- ### Intramesencephalic Segment
- Intraaxial segment resides within midbrain and extends from ONC to interpeduncular cistern
- CNIII fascicles course anteriorly at least partially through MLF, red nucleus, substantia nigra, and medial cerebral peduncle
- Oculomotor nerve fascicles converge in posterior-to-anterior direction
- Exit midbrain into interpeduncular cistern
- ### Interpeduncular Cisternal Segment
- Each CNIII leaves midbrain medially to cerebral peduncle in lateral part of interpeduncular fossa
- Each nerve may arise as tiny rootlets that immediately unite and extend as single root
- Cisternal segment extends from exit point of nerve along medial side of cerebral peduncle through interpeduncular and prepontine cisterns to posterior petroclinoid fold, posterior margin of oculomotor triangle
- Passes between posterior cerebral artery (PCA) above and superior cerebellar artery (SCA) below
- Courses inferior to posterior communicating artery and medial to free edge of tentorium cerebelli
- Measures ~ 2.1 mm in diameter within cistern
- Topographically, pupillary fibers are superficially located in cisternal portion of CNIII
- ### Petroclinoid Segment
- Located between cisternal and trigonal segments
- Defined posteriorly by posterior petroclinoid fold and anteriorly by oculomotor porus (opening) of roof of cavernous sinus
- Oculomotor triangle represents floor of petroclinoid segment
- ### Trigonal Segment
- Petroclinoid segment ends at oculomotor porus where nerve pierces roof of cavernous sinus, near center of oculomotor triangle
- Oculomotor cistern, CSF-filled arachnoid and dural cuff, begins at oculomotor porus and extends ~ 6 mm
- Trigonal segment of oculomotor nerve travels within oculomotor cistern as it enters superolateral cavernous sinus roof
- Trigonal segments terminates when nerve is incorporated into fibrous lateral wall of cavernous sinus
- Cistern and trigonal segment is recognized surgically as avascular space used to mobilize nerve during cavernous sinus surgery
- ### Cavernous Segment
- Incorporated into lateral dural wall of cavernous sinus just under tip of anterior clinoid process
- This wall consists of 2 layers
- Superficial dense and formed from dura
- Deep endosteal layer that invests nerves running in lateral wall
- Cavernous segment on CNIII extends just past anterior clinoid process where SOF begins
- Carotid-oculomotor membrane: Layer of dura that lines lower margin of anterior clinoid process and extends medially to form proximal dural ring; it separates lower margin of anterior clinoid process from cavernous segment CNIII and extends medially around carotid artery
- CNIII remains most cephalad of all cranial nerves within cavernous sinus
- CNIII superolateral to cavernous internal carotid artery
- ~ 14 mm in length
- ### Fissural Segment
- CNIII courses along lateral margin of optic strut as it passes through medial part of SOF
- Fissural segment of oculomotor nerve splits into its superior and inferior divisions
- ~ 6 mm long
- Fissural segment extends from anterior clinoid process to oculomotor foramen of SOF
- ### Orbital Segment
- Superior and inferior branches of CNIII enter orbit through SOF and pass through annulus tendineus (annulus of Zinn)
- Annulus of Zinn partially segments SOF into lateral component and medial component; medial component is referred to as oculomotor foramen
- Superior branch supplies levator palpebrae superioris and superior rectus muscles
- Inferior branch supplies inferior rectus, medial rectus, and inferior oblique muscles
- Preganglionic parasympathetic fibers follow inferior branch to ciliary ganglion of orbit
- Postganglionic parasympathetic fibers continue as short ciliary nerves to enter globe with optic nerve
- In globe, short ciliary nerves to ciliary body and iris
- Control papillary sphincter function and accommodation via ciliary muscle
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Bone CT best for skull base, bony foramina
- MR for intraaxial, cisternal, cavernous segments
- Thin-section, high-resolution T2 MR sequences in axial and coronal planes
- Depicts cisternal CNIII surrounded by CSF with high contrast and high spatial resolution
- ### Imaging Sweet Spots
- CNIII nuclear complex and intraaxial segment not directly visualized
- Find periaqueductal gray matter to localize
- Identification of distal basilar artery and branches can be reliable landmark for finding cisternal CNIII; it passes between posterior cerebral artery above and SCA below
- ### Imaging Pitfalls
- Negative MR and MRA does **not** completely exclude posterior communicating artery aneurysm
- CTA or conventional angiography recommended to exclude this diagnosis
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Uncal herniation pushes CNIII on petroclinoid ligament
- During trauma, downward shift of brainstem upon impact can stretch CNIII over petroclinoid ligament
- CNIII susceptible to compression by PCA aneurysms
- CNIII neuropathy divided into **simple** if isolated and **complex** if with other CN involvement (CNIV and CNVI)
- **Simple** CNIII with pupillary involvement
- Must exclude **PCA** **aneurysm**as cause
- Explanation: Parasympathetic fibers are peripherally distributed
- Simple CNIII with pupillary sparing
- Presumed microvascular infarction involves vessels supplying core of nerve with relative sparing of peripheral pupillary fibers
e76492c9-de5b-4440-9851-aade10b64f23
## Images
### Graphics
![Sagittal graphic shows the oculomotor nerve exiting from the anterior brainstem. After passing medially to the trochlear nerve (CNIV) between the superior cerebellar artery and posterior cerebral artery, it enters the cavernous sinus. CNIII is the most superior nerve coursing through the cavernous sinus. Once in orbit, it divides into the superior and inferior divisions. Preganglionic parasympathetic fibers travel with the inferior division to join the ciliary ganglion.](images/app.statdx.com_image_thumbnail_d22ac9d9-f51e-4ddd-bcdc-13d01ea74a64_annotated_false_size_900_quality_90_5cd6f24594a33fd3fdc0faf95da3f8f2ee0a59df.jpg)
*Sagittal graphic shows the oculomotor nerve exiting from the anterior brainstem. After passing medially to the trochlear nerve (CNIV) between the superior cerebellar artery and posterior cerebral artery, it enters the cavernous sinus. CNIII is the most superior nerve coursing through the cavernous sinus. Once in orbit, it divides into the superior and inferior divisions. Preganglionic parasympathetic fibers travel with the inferior division to join the ciliary ganglion.*
![Sagittal graphic shows the oculomotor nerve exiting from the anterior brainstem. After passing medially to the trochlear nerve (CNIV) between the superior cerebellar artery and posterior cerebral artery, it enters the cavernous sinus. CNIII is the most superior nerve coursing through the cavernous sinus. Once in orbit, it divides into the superior and inferior divisions. Preganglionic parasympathetic fibers travel with the inferior division to join the ciliary ganglion.](images/app.statdx.com_image_thumbnail_d22ac9d9-f51e-4ddd-bcdc-13d01ea74a64_size_174_quality_85_e1d78f7aab1f5aa53ece4c00e5826ca9ba7176de.jpg)
*Sagittal graphic shows the oculomotor nerve exiting from the anterior brainstem. After passing medially to the trochlear nerve (CNIV) between the superior cerebellar artery and posterior cerebral artery, it enters the cavernous sinus. CNIII is the most superior nerve coursing through the cavernous sinus. Once in orbit, it divides into the superior and inferior divisions. Preganglionic parasympathetic fibers travel with the inferior division to join the ciliary ganglion.*
![Sagittal graphic shows the oculomotor nerve exiting from the anterior brainstem. After passing medially to the trochlear nerve (CNIV) between the superior cerebellar artery and posterior cerebral artery, it enters the cavernous sinus. CNIII is the most superior nerve coursing through the cavernous sinus. Once in orbit, it divides into the superior and inferior divisions. Preganglionic parasympathetic fibers travel with the inferior division to join the ciliary ganglion.](images/app.statdx.com_image_thumbnail_d22ac9d9-f51e-4ddd-bcdc-13d01ea74a64_size_174_quality_85_f32ea936_20251018T124943Z.jpg)
*Sagittal graphic shows the oculomotor nerve exiting from the anterior brainstem. After passing medially to the trochlear nerve (CNIV) between the superior cerebellar artery and posterior cerebral artery, it enters the cavernous sinus. CNIII is the most superior nerve coursing through the cavernous sinus. Once in orbit, it divides into the superior and inferior divisions. Preganglionic parasympathetic fibers travel with the inferior division to join the ciliary ganglion.*
![Axial graphic clearly depicts CNIII originating from the oculomotor nuclei complex to travel through the medial aspect of the red nucleus and substantia nigra before exiting into the interpeduncular cistern. After traversing the cavernous sinus, surrounded by the CSF-filled oculomotor cistern, it enters the orbit through the superior orbital fissure, dividing into superior and inferior branches and passing through the annulus tendineus (annulus of Zinn).](images/app.statdx.com_image_thumbnail_51343cac-f815-4ed5-b9de-967f7130809d_annotated_false_size_900_quality_90_436ca2e8e7a21633e672c0aea0fbc5901def6d31.jpg)
*Axial graphic clearly depicts CNIII originating from the oculomotor nuclei complex to travel through the medial aspect of the red nucleus and substantia nigra before exiting into the interpeduncular cistern. After traversing the cavernous sinus, surrounded by the CSF-filled oculomotor cistern, it enters the orbit through the superior orbital fissure, dividing into superior and inferior branches and passing through the annulus tendineus (annulus of Zinn).*
### Axial T2 MR
![First of 3 axial 3D T2 SPACE MR images shows bilateral CNIII emerging out of the anterior midbrain into the interpeduncular cistern. Each nerve may arise as tiny rootlets that immediately unite and extend as single root.](images/app.statdx.com_image_thumbnail_010d1a33-f615-4c80-8d67-712c7a954756_annotated_false_size_900_quality_90_f9df1c52546d045cf0af8d9fc24613f2a33697fa.jpg)
*First of 3 axial 3D T2 SPACE MR images shows bilateral CNIII emerging out of the anterior midbrain into the interpeduncular cistern. Each nerve may arise as tiny rootlets that immediately unite and extend as single root.*
![The cisternal segment extends from the exit point of CNIII along the medial side of the cerebral peduncle through the interpeduncular and prepontine cisterns to the posterior petroclinoid fold, posterior margin of oculomotor triangle.](images/app.statdx.com_image_thumbnail_28b34984-f83f-4cdf-a1d0-55b11cfbf026_annotated_false_size_900_quality_90_f053206a33fff245d56d1dfed8de8ebf4e3839c8.jpg)
*The cisternal segment extends from the exit point of CNIII along the medial side of the cerebral peduncle through the interpeduncular and prepontine cisterns to the posterior petroclinoid fold, posterior margin of oculomotor triangle.*
![The cisternal segment of CNIII then passes between the posterior cerebral artery (PCA) above and the superior cerebellar artery (SCA) below and courses inferior to the posterior communicating artery and medial to the free edge of the tentorium cerebelli.](images/app.statdx.com_image_thumbnail_2dcee6a4-3f05-44f0-96a1-ced1171892c5_annotated_false_size_900_quality_90_173e26e57cf4e157eeb4b7b3c7abe4962253053c.jpg)
*The cisternal segment of CNIII then passes between the posterior cerebral artery (PCA) above and the superior cerebellar artery (SCA) below and courses inferior to the posterior communicating artery and medial to the free edge of the tentorium cerebelli.*
### Axial T2 & T1 MR
![First of 2 axial 3D T2 SPACE MR images shows the distal cisternal segments of CNIII coursing parallel and inferior to the posterior communicating artery. Topographically pupillary fibers are located superficially along the nerve and are prone to dysfunction by extrinsic compression, particularly by posterior communicating aneurysm.](images/app.statdx.com_image_thumbnail_28a24d7e-1801-4584-be93-99a51087955d_annotated_false_size_900_quality_90_2359d9d0193ea18abe2bc5deddc75451bca2ab08.jpg)
*First of 2 axial 3D T2 SPACE MR images shows the distal cisternal segments of CNIII coursing parallel and inferior to the posterior communicating artery. Topographically pupillary fibers are located superficially along the nerve and are prone to dysfunction by extrinsic compression, particularly by posterior communicating aneurysm.*
![The trigonal segment of CNIII begins when the distal petroclinoid segment enters the oculomotor cistern through the oculomotor porus and terminates when the nerve is incorporated into the fibrous lateral wall of the cavernous sinus.](ab286a60-3791-407f-8c58-8883f674aab2)
*The trigonal segment of CNIII begins when the distal petroclinoid segment enters the oculomotor cistern through the oculomotor porus and terminates when the nerve is incorporated into the fibrous lateral wall of the cavernous sinus.*
![Axial 3D IR T1 MR through the brainstem at the level of superior colliculus is shown. The paired oculomotor nuclear complex is not directly visualized; however, since it is partially embedded in the periaqueductal gray matter anterior to the cerebral aqueduct at the level of the superior colliculus, its position can be inferred by these landmarks. The approximate location of the oculomotor nucleus is marked on the left.](4ca16d48-bfeb-4e9f-ad3c-7174c2d7218d)
*Axial 3D IR T1 MR through the brainstem at the level of superior colliculus is shown. The paired oculomotor nuclear complex is not directly visualized; however, since it is partially embedded in the periaqueductal gray matter anterior to the cerebral aqueduct at the level of the superior colliculus, its position can be inferred by these landmarks. The approximate location of the oculomotor nucleus is marked on the left.*
### Coronal T2 MR
![First of 3 coronal reformat 3D T2 SPACE MR images shows CNIII emerging from the midbrain along the lateral aspect of the interpeduncular cistern. This marks the end of the intramesencephalic and the beginning of the interpeduncular segment of CNIII.](1a08daf3-5e03-4512-b94f-0e33915ab3c9)
*First of 3 coronal reformat 3D T2 SPACE MR images shows CNIII emerging from the midbrain along the lateral aspect of the interpeduncular cistern. This marks the end of the intramesencephalic and the beginning of the interpeduncular segment of CNIII.*
![The cisternal segments of CNIII travel anteriorly and laterally to the posterior petroclinoid fold, posterior margin of oculomotor triangle.](fcbe8c53-4b3c-4d61-a9c3-2ae5b5f1b44b)
*The cisternal segments of CNIII travel anteriorly and laterally to the posterior petroclinoid fold, posterior margin of oculomotor triangle.*
![After emerging from the midbrain, the cisternal segments of CNIII travel anteriorly between the posterior cerebral and superior cerebellar arteries medial to CNIV.](dd4ec0ab-899c-43b5-ab18-63a269097a47)
*After emerging from the midbrain, the cisternal segments of CNIII travel anteriorly between the posterior cerebral and superior cerebellar arteries medial to CNIV.*
![First of 3 coronal reformat 3D T2 SPACE MR images shows the petroclinoid segments of bilateral CNIII. The petroclinoid segments are located between the cisternal and trigonal segments. The oculomotor triangle forms the floor of the petroclinoid segment.](a03fcd8b-b79a-4d30-8d17-0d80ffe6bb85)
*First of 3 coronal reformat 3D T2 SPACE MR images shows the petroclinoid segments of bilateral CNIII. The petroclinoid segments are located between the cisternal and trigonal segments. The oculomotor triangle forms the floor of the petroclinoid segment.*
![The petroclinoid segment of CNIII is seen entering the oculomotor cistern through the oculomotor porus. The oculomotor cistern is a CSF-filled arachnoid and dural cuff, which begins at the oculomotor porus and extends ~ 6 mm.](d0c3af12-28dd-46ee-880e-ef1acdf41198)
*The petroclinoid segment of CNIII is seen entering the oculomotor cistern through the oculomotor porus. The oculomotor cistern is a CSF-filled arachnoid and dural cuff, which begins at the oculomotor porus and extends ~ 6 mm.*
![Bilateral CNIII trigonal segments are seen in the oculomotor cisterns. The trigonal segments terminate when the nerve is incorporated into the fibrous lateral wall of the cavernous sinus. The cavernous segment passes through the lateral wall of the cavernous sinus and through the superior orbital fissure along the lateral margin of the optic strut forming the fissural segment. The fissural segment splits into superior and inferior branches, which pass into orbit through the annulus of Zinn.](964f0514-bb96-44a8-bcd0-dba9173b16a6)
*Bilateral CNIII trigonal segments are seen in the oculomotor cisterns. The trigonal segments terminate when the nerve is incorporated into the fibrous lateral wall of the cavernous sinus. The cavernous segment passes through the lateral wall of the cavernous sinus and through the superior orbital fissure along the lateral margin of the optic strut forming the fissural segment. The fissural segment splits into superior and inferior branches, which pass into orbit through the annulus of Zinn.*
### Clinical Correlation
![3D volume-rendered reconstruction of catheter angiogram with right carotid injection shows a large bilobed paraposterior communicating artery (PCom) internal carotid artery aneurysm. This patient presented with CNIII palsy with involvement of superficial pupillary fibers.](c25f4972-70ab-4ee9-8cd9-9e7f2eb8c685)
*3D volume-rendered reconstruction of catheter angiogram with right carotid injection shows a large bilobed paraposterior communicating artery (PCom) internal carotid artery aneurysm. This patient presented with CNIII palsy with involvement of superficial pupillary fibers.*
![Axial T1 C+ FS MR though the level of the interpeduncular cistern demonstrates abnormal thickening and enhancement of the cisternal CNIII as tumor extends in retrograde fashion along the nerve from the cavernous sinus. This middle-aged man with a history of squamous cell carcinoma of the left forehead subsequently developed progressive disease of the orbit, and perineural tumor spread to the superior orbital fissure and cavernous sinus.](c2fd06e7-6ace-401c-8acb-6589d8d3ee83)
*Axial T1 C+ FS MR though the level of the interpeduncular cistern demonstrates abnormal thickening and enhancement of the cisternal CNIII as tumor extends in retrograde fashion along the nerve from the cavernous sinus. This middle-aged man with a history of squamous cell carcinoma of the left forehead subsequently developed progressive disease of the orbit, and perineural tumor spread to the superior orbital fissure and cavernous sinus.*
![Axial 3D MPRAGE T1 C+ MR demonstrates smooth enhancement of bilateral CNIII cisternal segments in a patient with known Lyme disease.](98bfff56-25ab-4d9a-96f1-c4d96732f4d9)
*Axial 3D MPRAGE T1 C+ MR demonstrates smooth enhancement of bilateral CNIII cisternal segments in a patient with known Lyme disease.*
### Additional Images
![Coronal T1 C+ FS MR in a patient with chronic calcified lesion in the left cavernous sinus (presumed to be meningioma) demonstrates chronic atrophy of the extraocular muscles on the left secondary to oculomotor denervation. Notice there is preservation of the superior oblique muscle (CNIV) <img src='img/arrows/WS.png' alt='white solid arrow'/> and lateral rectus muscle (CNVI) <img src='img/arrows/WC.png' alt='white curved arrow'/>. Optic nerves <img src='img/arrows/WO.png' alt='white open arrow'/> are noted.](9888cd5d-25e0-41c6-b932-f42688f7f02a)
*Coronal T1 C+ FS MR in a patient with chronic calcified lesion in the left cavernous sinus (presumed to be meningioma) demonstrates chronic atrophy of the extraocular muscles on the left secondary to oculomotor denervation. Notice there is preservation of the superior oblique muscle (CNIV) <img src='img/arrows/WS.png' alt='white solid arrow'/> and lateral rectus muscle (CNVI) <img src='img/arrows/WC.png' alt='white curved arrow'/>. Optic nerves <img src='img/arrows/WO.png' alt='white open arrow'/> are noted.*
![Coronal CECT in a patient with chronic calcified lesion in the left cavernous sinus (presumed to be meningioma) demonstrates chronic atrophy of the extraocular muscles on the left secondary to CNIII denervation. Notice there is preservation of superior oblique muscle (CNIV) <img src='img/arrows/WS.png' alt='white solid arrow'/> and lateral rectus muscle (CNVI) <img src='img/arrows/WC.png' alt='white curved arrow'/>. Optic nerves <img src='img/arrows/WO.png' alt='white open arrow'/> are noted.](66777c5b-e652-4ca6-b122-73775070bf4f)
*Coronal CECT in a patient with chronic calcified lesion in the left cavernous sinus (presumed to be meningioma) demonstrates chronic atrophy of the extraocular muscles on the left secondary to CNIII denervation. Notice there is preservation of superior oblique muscle (CNIV) <img src='img/arrows/WS.png' alt='white solid arrow'/> and lateral rectus muscle (CNVI) <img src='img/arrows/WC.png' alt='white curved arrow'/>. Optic nerves <img src='img/arrows/WO.png' alt='white open arrow'/> are noted.*
![Axial DWI MR in a patient with acute onset of isolated right 3rd nerve palsy demonstrates 2 tiny foci of diffusion restriction. The more posterior lesion is near the expected location of the motor nuclei of the oculomotor nerve <img src='img/arrows/WS.png' alt='white solid arrow'/>. The more anterior focus likely involves the intramesencephalic fibers of the oculomotor nerve just prior to exiting the midbrain at the interpeduncular cistern <img src='img/arrows/WC.png' alt='white curved arrow'/>.](42483ad8-9120-4059-a25d-aae794938faf)
*Axial DWI MR in a patient with acute onset of isolated right 3rd nerve palsy demonstrates 2 tiny foci of diffusion restriction. The more posterior lesion is near the expected location of the motor nuclei of the oculomotor nerve <img src='img/arrows/WS.png' alt='white solid arrow'/>. The more anterior focus likely involves the intramesencephalic fibers of the oculomotor nerve just prior to exiting the midbrain at the interpeduncular cistern <img src='img/arrows/WC.png' alt='white curved arrow'/>.*
![First of 6 axial T2 MR images presented from inferior to superior demonstrates the oculomotor nerves entering the oculomotor cisterns in the posterior roof of the cavernous sinus. Notice the nerves are surrounded by high-signal cerebrospinal fluid. From here, the oculomotor nerves course anteriorly in the lateral wall of the cavernous sinus above the trochlear nerve and enters orbit via the superior orbital fissure.](62446da6-6ebd-4ede-8a83-3065e968d777)
*First of 6 axial T2 MR images presented from inferior to superior demonstrates the oculomotor nerves entering the oculomotor cisterns in the posterior roof of the cavernous sinus. Notice the nerves are surrounded by high-signal cerebrospinal fluid. From here, the oculomotor nerves course anteriorly in the lateral wall of the cavernous sinus above the trochlear nerve and enters orbit via the superior orbital fissure.*
![Oculomotor nerves course anteriorly through the prepontine cistern inferolateral to the posterior communicating artery and medial to the uncus of the temporal lobe. The left oculomotor nerve is seen passing below the posterior cerebral artery.](b9777e90-e0b6-4a34-ba60-4403531ab945)
*Oculomotor nerves course anteriorly through the prepontine cistern inferolateral to the posterior communicating artery and medial to the uncus of the temporal lobe. The left oculomotor nerve is seen passing below the posterior cerebral artery.*
![After exiting the brainstem, the oculomotor nerves course anteriorly through the interpeduncular and prepontine cisterns toward the cavernous sinus, passing between the posterior cerebral and superior cerebellar arteries.](00ba2e40-240e-45c7-8728-1ab56246db9f)
*After exiting the brainstem, the oculomotor nerves course anteriorly through the interpeduncular and prepontine cisterns toward the cavernous sinus, passing between the posterior cerebral and superior cerebellar arteries.*
![Axial T2 MR shows both oculomotor nerves coursing through the interpeduncular cistern.](2ec3cf95-bc03-4011-9622-b6fa73ea4589)
*Axial T2 MR shows both oculomotor nerves coursing through the interpeduncular cistern.*
![Oculomotor nerves exit midbrain from the medial surface of the cerebral peduncle to enter the interpeduncular cistern and continue anteriorly underneath the posterior cerebral arteries.](0bbb488a-ab3f-4354-8198-70eed40b209f)
*Oculomotor nerves exit midbrain from the medial surface of the cerebral peduncle to enter the interpeduncular cistern and continue anteriorly underneath the posterior cerebral arteries.*
![First of 6 coronal T2 MR images presented from posterior to anterior reveals the most proximal aspects of both oculomotor nerves exiting the midbrain from the medial surface of the cerebral peduncle to enter the interpeduncular cistern.](ae5089ab-b02d-410f-bb95-25297c58bb16)
*First of 6 coronal T2 MR images presented from posterior to anterior reveals the most proximal aspects of both oculomotor nerves exiting the midbrain from the medial surface of the cerebral peduncle to enter the interpeduncular cistern.*
![Oculomotor nerves often emerge from the midbrain by several rootlets, as seen on this coronal T2 MR, which subsequently fuse to form a single trunk.](a3a6ba47-2381-479e-9ac2-50118943fa4b)
*Oculomotor nerves often emerge from the midbrain by several rootlets, as seen on this coronal T2 MR, which subsequently fuse to form a single trunk.*
![Oculomotor nerves pass between the posterior cerebral artery above and superior cerebellar artery below. The proximity of the oculomotor nerve to the uncus makes the nerve vulnerable to injury through uncal herniation. Its nearness to the posterior communicating, posterior cerebral, and superior cerebellar arteries makes it easily injured by an aneurysm.](5193cf0c-3d8a-4ced-8df6-b79f6a8f2871)
*Oculomotor nerves pass between the posterior cerebral artery above and superior cerebellar artery below. The proximity of the oculomotor nerve to the uncus makes the nerve vulnerable to injury through uncal herniation. Its nearness to the posterior communicating, posterior cerebral, and superior cerebellar arteries makes it easily injured by an aneurysm.*
![Oculomotor nerves are seen coursing through the interpeduncular cistern toward the cavernous sinus closely related to the posterior communicating artery. An aneurysm of the posterior communicating artery can result in compression of the oculomotor nerve. The lateral margin of the Liliequist membrane attaches to the arachnoidal sheath surrounding oculomotor nerves.](229c3e22-30b4-4796-8a13-0f4abe4c8c6b)
*Oculomotor nerves are seen coursing through the interpeduncular cistern toward the cavernous sinus closely related to the posterior communicating artery. An aneurysm of the posterior communicating artery can result in compression of the oculomotor nerve. The lateral margin of the Liliequist membrane attaches to the arachnoidal sheath surrounding oculomotor nerves.*
![The oculomotor nerve crosses the petroclinoid ligament and is situated medial to and slightly beneath the level of the free edge of the tentorium at the point of entry into the roof of the cavernous sinus.](dec8460d-2d72-4559-b973-504917f93944)
*The oculomotor nerve crosses the petroclinoid ligament and is situated medial to and slightly beneath the level of the free edge of the tentorium at the point of entry into the roof of the cavernous sinus.*
![A short length of the oculomotor nerve is surrounded by a dural and arachnoid cuff to create the oculomotor cistern within the roof and lateral wall of the cavernous sinus. The oculomotor nerve courses anteriorly above the trochlear nerve within the lateral wall of the cavernous sinus and enters the orbit via the superior orbital fissure.](4d057dbf-beba-4424-9a72-b63988fd2549)
*A short length of the oculomotor nerve is surrounded by a dural and arachnoid cuff to create the oculomotor cistern within the roof and lateral wall of the cavernous sinus. The oculomotor nerve courses anteriorly above the trochlear nerve within the lateral wall of the cavernous sinus and enters the orbit via the superior orbital fissure.*
![Axial T1 C+ MR in a patient with acute lymphocytic leukemia and leukemic infiltration of several cranial nerves, including bilateral CNIII, is shown. The nerves show enlargement and abnormal enhancement of the cisternal portions, left worse than right. Notice the proximal posterior cerebral arteries pass medial to the cisternal CNIII and then pass over the nerves en route to the occipital lobes.](b08eeb81-3794-45bd-bd39-db8ecda3c607)
*Axial T1 C+ MR in a patient with acute lymphocytic leukemia and leukemic infiltration of several cranial nerves, including bilateral CNIII, is shown. The nerves show enlargement and abnormal enhancement of the cisternal portions, left worse than right. Notice the proximal posterior cerebral arteries pass medial to the cisternal CNIII and then pass over the nerves en route to the occipital lobes.*
![CTA with 3D reformation in a patient with new-onset right-sided 3rd nerve palsy demonstrates bilateral posterior communicating artery origin aneurysms, right greater than left. Posterior communicating artery origin aneurysms classically cause 3rd nerve palsy with associated pupillary dysfunction.](63d95ebe-7338-4370-adf3-e96c1046b47e)
*CTA with 3D reformation in a patient with new-onset right-sided 3rd nerve palsy demonstrates bilateral posterior communicating artery origin aneurysms, right greater than left. Posterior communicating artery origin aneurysms classically cause 3rd nerve palsy with associated pupillary dysfunction.*
docs_md/articles/cniv-trochlear-nerve_52486223-9cb5-43f5-b9af-c46431ae6637.md
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---
title: "CNIV (Trochlear Nerve)"
docid: "52486223-9cb5-43f5-b9af-c46431ae6637"
authors:
- key: "b2e6dabb-ee1c-42a4-a332-9f0814c1c607"
value: "Surjith Vattoth, MD"
- key: "94f835c8-fa13-4e8a-995b-53048e6b0605"
value: "Philip R. Chapman, MD"
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name: "Head and Neck"
slug: "head-and-neck"
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name: "Anatomy"
slug: "anatomy"
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name: "Cranial Nerves"
slug: "cranial-nerves"
treeNodeId: "bc7da3a0-2ad7-4f30-949a-0db0d1e6f620"
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name: "CNIV (Trochlear Nerve)"
slug: "cniv-trochlear-nerve"
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category: "Head and Neck"
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lastUpdated: "12/19/23"
pageDescription: "CNIV (Trochlear Nerve)"
pageKeywords: "Head and Neck, Anatomy, Cranial Nerves, CNIV (Trochlear Nerve)"
pageTitle: "CNIV (Trochlear Nerve) | STATdx"
enhancedTitle: "CNIV (Trochlear Nerve)"
type: "ANATOMY"
breadcrumbs:
- "Head and Neck"
- "Anatomy"
- "Cranial Nerves"
- "CNIV (Trochlear Nerve)"
---
## TERMINOLOGY
- ### Abbreviations
- Trochlear nerve: CNIV
- ### Synonyms
- 4th cranial nerve
- ### Definitions
- CNIV: Motor nerve to superior oblique muscle
## IMAGING ANATOMY
- ### Overview
- Pure motor nerve (general somatic efferent) that innervates extraocular **superior oblique muscle**
- Segments: Intramesencephalic, cisternal, tentorial, cavernous, & extracranial
- Longest intracranial cranial nerve (CN) course (≈ 60 mm)
- Thinnest CN: 0.4- to 0.5-mm nerve diameter in cisternal segment
- ### Trochlear Nuclei
- Paired nuclei located in paramedian midbrain, **ventral to cerebral aqueduct of Sylvius**, & immediately **dorsal to medial longitudinal fasciculus (MLF)**
- Caudal to oculomotor nuclei at level of inferior colliculus
- ### Intramesencephalic Segment
- Trochlear nerve fascicles course posteriorly & inferiorly around cerebral aqueduct
- Fibers then cross (**decussate**) within **superior medullary velum**(at roof of upper 4th ventricle)
- **Key concept**: Each superior oblique muscle innervated by ipsilateral CNIV that originates in **contralateral** trochlear nucleus
- CNIV exits dorsal midbrain just below **inferior colliculus**
- CNIV **only CN** to**exit dorsal brainstem**
- ### Cisternal Segment
- CNIV courses anterolaterally in through quadrigeminal & perimesencephalic cisterns
- Surrounded by CSF in subarachnoid space
- In perimesencephalic cistern, **passes between lateral**aspect of posterior cerebral artery (**PCA**) above & superior cerebellar artery (**SCA**) below, close to tentorium
- Inferior, more lateral to CNIII, which passes between medial aspect of PCA & SCA in interpeduncular cistern
- ### Tentorial Segment
- CNIV passes anteriorly into **trochlear groove (TG)** along lower surface of free edge of tentorium
- TG: 4- to 6-mm long depression along tentorial medial surface near free edge of tentorium
- Distance of TG from tentorial free edge on 7T MR study: 1.1-2.0 mm (mean: 1.5 mm)
- Depth of TG on 7T MR study: 0.4-0.9mm (mean: 0.6 mm)
- From TG, CNIV pierces dura of **posterior petroclinoid fold** near posterior margin of **oculomotor triangle**, along rostrolateral free edge of tentorium
- Oculomotor triangle formed by 3 dural folds
- Anterior & posterior petroclinoid folds (extending from tentorial edge at petrous apex to anterior & posterior clinoid processes, respectively)
- Interclinoid fold (from anterior clinoid process to posterior clinoid process)
- **Trochlear cistern**: CSF sleeve around trochlear nerve (CNIV) after piercing posterior petroclinoid fold, lying posteroinferior to oculomotor (CNIII) cistern
- CNIV wedged between posterior petroclinoid fold medially & anterior petroclinoid fold laterally in trochlear cistern
- ### Cavernous Segment
- CNIV enters roof of cavernous sinus (CS) in posterolateral apex of **oculomotor triangle**, just posterior to CNIII entry
- CNIV courses in **lateral wall** of CS inferior to CNIII, superior to CNV1
- ### Extracranial Segment
- CNIV enters orbit through **superior orbital fissure** together with CNIII & CNVI
- Crosses over CNIII & courses medially
- Passes **above** annulus of Zinn (CNIII & CNVI go through annulus)
- Supplies motor innervation to superior oblique muscle
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- CT best for skull base, bony foramina
- High-resolution MR best for brainstem, cisternal, cavernous, & intraorbital imaging
- Intraorbital segment not visualized by any imaging modality or sequence
- Nerve visualization on 7T MR study: Origin at brainstem 65%, cisternal segment 93%, tentorial segment 100%, cavernous segment 74%
- ### Imaging Sweet Spots
- CNIV nucleus & intraaxial segment not directly visualized
- Nuclei position inferred by identifying periaqueductal gray matter & cerebral aqueduct at level of inferior colliculi on high-resolution MR
- MR for intraaxial, cisternal, & cavernous segments
- Thin-section, high-resolution T2 & T1 C+ MR in axial & coronal planes
- Coronal imaging margins: 4th ventricle to anterior globe; axial imaging margins: Orbital roof-diencephalon to maxillary sinus roof-medulla
- ### Imaging Pitfalls
- Difficult to visualize normal CNIV despite best MR imaging
- During image interrogation by radiologist, view known landmarks along its course
- Midbrain → tentorial margin → CS → superior orbital fissure → extraconal orbit
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- CNIV neuropathy divided into **simple & complex**
- **Simple** CNIV neuropathy (isolated)
- Most common form; usually secondary to trauma
- Cisternal segment injury by free edge of tentorium cerebelli or from PCA or SCA aneurysm
- Contusion of superior medullary velum
- **Complex** CNIV neuropathy (associated with other CN injury, CNIII ± CNVI)
- Brainstem stoke or tumor
- CS thrombosis, tumor
- Orbital tumor
- ### Clinical Findings
- Paralysis of superior oblique muscle results in **extorsion** (outward rotation) of affected eye due to unopposed action of inferior oblique muscle
- Diplopia, weakness of downward gaze, neck pain from **compensatory head tilt to opposite side**
a1e579e4-a421-4a39-9df6-53da856e3d62
## Images
### Graphics
![Sagittal graphic shows that the trochlear nucleus gives rise to fibers that form the contralateral trochlear nerve. After exiting the dorsal brainstem, CNIV courses lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery. After its long cisternal course, CNIV enters the cavernous sinus and runs inferolateral to CNIII and superior to the ophthalmic division of the trigeminal nerve (CNV1).](images/app.statdx.com_image_thumbnail_395eaee1-4592-42ca-a868-38b5e85e6c3b_annotated_false_size_900_quality_90_76126e4f7f78a89d3e441f182d9746ab0d1bf17c.jpg)
*Sagittal graphic shows that the trochlear nucleus gives rise to fibers that form the contralateral trochlear nerve. After exiting the dorsal brainstem, CNIV courses lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery. After its long cisternal course, CNIV enters the cavernous sinus and runs inferolateral to CNIII and superior to the ophthalmic division of the trigeminal nerve (CNV1).*
![Sagittal graphic shows that the trochlear nucleus gives rise to fibers that form the contralateral trochlear nerve. After exiting the dorsal brainstem, CNIV courses lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery. After its long cisternal course, CNIV enters the cavernous sinus and runs inferolateral to CNIII and superior to the ophthalmic division of the trigeminal nerve (CNV1).](images/app.statdx.com_image_thumbnail_395eaee1-4592-42ca-a868-38b5e85e6c3b_size_174_quality_85_d06269c3e30ec5ebf2b5239fd1c7464952cc0e9b.jpg)
*Sagittal graphic shows that the trochlear nucleus gives rise to fibers that form the contralateral trochlear nerve. After exiting the dorsal brainstem, CNIV courses lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery. After its long cisternal course, CNIV enters the cavernous sinus and runs inferolateral to CNIII and superior to the ophthalmic division of the trigeminal nerve (CNV1).*
![Sagittal graphic shows that the trochlear nucleus gives rise to fibers that form the contralateral trochlear nerve. After exiting the dorsal brainstem, CNIV courses lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery. After its long cisternal course, CNIV enters the cavernous sinus and runs inferolateral to CNIII and superior to the ophthalmic division of the trigeminal nerve (CNV1).](images/app.statdx.com_image_thumbnail_395eaee1-4592-42ca-a868-38b5e85e6c3b_size_174_quality_85_e12c0567_20251018T124943Z.jpg)
*Sagittal graphic shows that the trochlear nucleus gives rise to fibers that form the contralateral trochlear nerve. After exiting the dorsal brainstem, CNIV courses lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery. After its long cisternal course, CNIV enters the cavernous sinus and runs inferolateral to CNIII and superior to the ophthalmic division of the trigeminal nerve (CNV1).*
![Axial graphic shows the trochlear nerves originating from the trochlear nuclei and decussating in the superior medullary velum. CNIV runs much more lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery close to tentorium, and continues inferolateral with CNIII through the cavernous sinus. It crosses over CNIII to enter orbit above the annulus of Zinn, then courses medially over the levator palpebrae muscle to innervate the superior oblique muscle.](images/app.statdx.com_image_thumbnail_ce2a0ec0-f6f2-4ae0-97c0-28c6d9a3580c_annotated_false_size_900_quality_90_d6771729d89e72259d298198df700e7b2138c629.jpg)
*Axial graphic shows the trochlear nerves originating from the trochlear nuclei and decussating in the superior medullary velum. CNIV runs much more lateral to the oculomotor nerve between the posterior cerebral artery and superior cerebellar artery close to tentorium, and continues inferolateral with CNIII through the cavernous sinus. It crosses over CNIII to enter orbit above the annulus of Zinn, then courses medially over the levator palpebrae muscle to innervate the superior oblique muscle.*
### Axial and sagittal 3D T2 MR
![Axial 3D T2 SPACE MR shows bilateral trochlear nerves (CNIV) exiting dorsal brainstem just below midbrain inferior colliculi. Trochlear nerve (CNIV) of each side arise in contralateral midbrain trochlear (CNIV) nucleus. Brainstem fibers of both nerves decussates within superior medullary velum and exit dorsal midbrain. Left trochlear nerve is seen passing around brainstem within quadrigeminal cistern and then perimesencephalic cistern, where it courses anteriorly below free edge of tentorium cerebelli in trochlear groove and further anteriorly to pierce posterior petroclinoid fold toward trochlear cistern. Trochlear nerve (CNIV) is thinnest and longest cranial nerve; it is unusual to see a reasonable distance of its course in a single axial section, as seen here. It can be easily confused with tiny arteries and veins. Note the bigger oculomotor nerve (CNIII) anteriorly in interpeduncular cistern.](images/app.statdx.com_image_thumbnail_e519bdd2-ca92-4bb9-a21c-8efe33dea889_annotated_false_size_900_quality_90_3bcd5c4b8a49c489b6b841351363b5f8d8d3a6ce.jpg)
*Axial 3D T2 SPACE MR shows bilateral trochlear nerves (CNIV) exiting dorsal brainstem just below midbrain inferior colliculi. Trochlear nerve (CNIV) of each side arise in contralateral midbrain trochlear (CNIV) nucleus. Brainstem fibers of both nerves decussates within superior medullary velum and exit dorsal midbrain. Left trochlear nerve is seen passing around brainstem within quadrigeminal cistern and then perimesencephalic cistern, where it courses anteriorly below free edge of tentorium cerebelli in trochlear groove and further anteriorly to pierce posterior petroclinoid fold toward trochlear cistern. Trochlear nerve (CNIV) is thinnest and longest cranial nerve; it is unusual to see a reasonable distance of its course in a single axial section, as seen here. It can be easily confused with tiny arteries and veins. Note the bigger oculomotor nerve (CNIII) anteriorly in interpeduncular cistern.*
![Sagittal 3D T2 SPACE MR shows trochlear nerve origin just below inferior colliculus of midbrain. Trochlear nerve is the only cranial nerve to exit dorsal brainstem.](images/app.statdx.com_image_thumbnail_cd43671b-6c49-437d-a714-43be1d2d8e5c_annotated_false_size_900_quality_90_b99bb83ac1c1ad1dece9c4dba4803c35f5713c9d.jpg)
*Sagittal 3D T2 SPACE MR shows trochlear nerve origin just below inferior colliculus of midbrain. Trochlear nerve is the only cranial nerve to exit dorsal brainstem.*
![Further left parasagittal reformat of 3D T2 SPACE MR shows CNIV near trochlear groove inferomedial to tentorial free edge.](images/app.statdx.com_image_thumbnail_00526011-ba17-4b20-9a9c-fea8f4b6a0e7_annotated_false_size_900_quality_90_67ed6637062eecb810823b69e9cbb5ba9407b80a.jpg)
*Further left parasagittal reformat of 3D T2 SPACE MR shows CNIV near trochlear groove inferomedial to tentorial free edge.*
### Coronal T2 MR
![First of 3 coronal reformatted images of a 3D T2 SPACE MR from posterior to anterior shows the left trochlear nerve (CNIV) exiting the dorsal brainstem just below the inferior colliculus into the quadrigeminal cistern.](63211774-85f3-470e-b820-577783f3812d)
*First of 3 coronal reformatted images of a 3D T2 SPACE MR from posterior to anterior shows the left trochlear nerve (CNIV) exiting the dorsal brainstem just below the inferior colliculus into the quadrigeminal cistern.*
![This image shows the left trochlear nerve in the perimesencephalic cistern and the right trochlear nerve exiting the brainstem.](1915dab1-81a5-4ff6-b1d9-64e9602a4a0e)
*This image shows the left trochlear nerve in the perimesencephalic cistern and the right trochlear nerve exiting the brainstem.*
![Most anterior of the 3 coronal reformatted images shows the left trochlear nerve in the trochlear groove inferomedial to the tentorial free edge. Note the parahippocampal gyrus is superolateral and cerebellum inferolateral to the tentorial leaflet. The entire course of the trochlear nerves is not always visualized on clinical MR; 7T MR offers better extent of visualization, but not in its entirety. Do not confuse tiny vessels for the trochlear nerve. The trochlear nerve passes between the posterior cerebral artery (PCA) and superior cerebellar artery (SCA) laterally in the perimesencephalic cistern. CNIII passes in between the PCA and SCA near the arterial origins more medially in the anterior perimesencephalic/interpeduncular cisterns. Basal vein of Rosenthal also courses through the upper perimesencephalic cistern.](8c9738be-a794-4144-b5be-904bc4f2d39e)
*Most anterior of the 3 coronal reformatted images shows the left trochlear nerve in the trochlear groove inferomedial to the tentorial free edge. Note the parahippocampal gyrus is superolateral and cerebellum inferolateral to the tentorial leaflet. The entire course of the trochlear nerves is not always visualized on clinical MR; 7T MR offers better extent of visualization, but not in its entirety. Do not confuse tiny vessels for the trochlear nerve. The trochlear nerve passes between the posterior cerebral artery (PCA) and superior cerebellar artery (SCA) laterally in the perimesencephalic cistern. CNIII passes in between the PCA and SCA near the arterial origins more medially in the anterior perimesencephalic/interpeduncular cisterns. Basal vein of Rosenthal also courses through the upper perimesencephalic cistern.*
### Additional Images
![First of 3 axial T2 MR images presented from inferior to superior through the midbrain is shown. The left trochlear nerve passes around the brainstem within the ambient cistern, where it courses anteriorly below the tentorium cerebelli. The trochlear nerves decussate in the superior medullary velum with fibers from the nucleus passing to the contralateral CNIV.](da36b9a6-7284-4ae8-9126-ac9d754e9082)
*First of 3 axial T2 MR images presented from inferior to superior through the midbrain is shown. The left trochlear nerve passes around the brainstem within the ambient cistern, where it courses anteriorly below the tentorium cerebelli. The trochlear nerves decussate in the superior medullary velum with fibers from the nucleus passing to the contralateral CNIV.*
![Trochlear nerve (CNIV) is the smallest cranial nerve and is not routinely visualized. In addition, the trochlear nerve may easily be confused with numerous small arteries and veins in the ambient cistern.](938d19dc-fa7d-4740-b601-217d02bbe4bb)
*Trochlear nerve (CNIV) is the smallest cranial nerve and is not routinely visualized. In addition, the trochlear nerve may easily be confused with numerous small arteries and veins in the ambient cistern.*
![After decussating in the superior medullary velum, the trochlear nerve exits the dorsal surface of the brainstem below the inferior colliculus to enter the quadrigeminal plate cistern. The trochlear nerve is the only cranial nerve to exit the dorsal brainstem.](de70d55d-0873-4bcd-bb27-b4ca84de1ce5)
*After decussating in the superior medullary velum, the trochlear nerve exits the dorsal surface of the brainstem below the inferior colliculus to enter the quadrigeminal plate cistern. The trochlear nerve is the only cranial nerve to exit the dorsal brainstem.*
![First of 3 coronal T2 MR images from posterior to anterior through the brainstem demonstrates the right trochlear nerve exiting from the dorsal brainstem below the inferior colliculus to enter the quadrigeminal plate cistern. The left trochlear nerve is obscured by the lateral mesencephalic vein.](7fd53663-64ba-4e68-9488-89c47801a77a)
*First of 3 coronal T2 MR images from posterior to anterior through the brainstem demonstrates the right trochlear nerve exiting from the dorsal brainstem below the inferior colliculus to enter the quadrigeminal plate cistern. The left trochlear nerve is obscured by the lateral mesencephalic vein.*
![Trochlear nerves can be visualized bilaterally coursing anteriorly within the ambient cistern below the free margin of the tentorium cerebelli. Only very focused thin-section high-resolution T2 MR imaging has any chance of seeing CNIV in this location.](f3e8d50d-4cce-46c2-8ce4-3643e92b8ebe)
*Trochlear nerves can be visualized bilaterally coursing anteriorly within the ambient cistern below the free margin of the tentorium cerebelli. Only very focused thin-section high-resolution T2 MR imaging has any chance of seeing CNIV in this location.*
![At the level of the basilar artery, the trochlear nerve is hidden on the left but visible on the right inferolateral to the oculomotor nerve. Both nerves pass between the posterior cerebral artery and the superior cerebellar artery.](91cf7ec3-14b1-4f97-8bcc-f6518729a606)
*At the level of the basilar artery, the trochlear nerve is hidden on the left but visible on the right inferolateral to the oculomotor nerve. Both nerves pass between the posterior cerebral artery and the superior cerebellar artery.*
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title: "CNIX (Glossopharyngeal Nerve)"
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---
## TERMINOLOGY
- ### Abbreviations
- Glossopharyngeal nerve (CNIX)
- ### Synonyms
- 9th cranial nerve, CN9
- ### Definitions
- Mixed nerve with complex functions
- Taste & sensation to posterior 1/3 of tongue
- Sensory nerve to middle ear & pharynx
- Parasympathetic to parotid gland
- Motor to stylopharyngeus muscle
- Viscerosensory to carotid body & sinus
## IMAGING ANATOMY
- ### Overview
- 4 segments: Intraaxial, cisternal, skull base, & extracranial
- ### Intraaxial Segment
- Glossopharyngeal nuclei in upper & middle medulla
- **Motor fibers** to stylopharyngeus muscle from **nucleus ambiguus**
- **Sensory fibers** from tympanic membrane, soft palate, tongue base, & pharynx terminate in **spinal nucleus CNV**
- **Taste****fibers** from posterior 1/3 of tongue terminate in **solitary tract nucleus**
- **Parasympathetic fibers** to parotid gland originate in **inferior saliva****to****ry nucleus**
- ### Cisternal Segment
- Exits lateral medulla in **postolivary sulcus** as 3-5 rootlets uniting to form cisternal segment just above vagus nerve
- Mean length from medulla to jugular foramen: ~ 14-18 mm
- Transition zone (TZ) located ~ 1.1-1.8 mm from medulla or root entry/exit zone (REZ)
- TZ: Area between central & peripheral myelin with increased vulnerability to mechanical irritation & relevant in neurovascular compression
- REZ: Portion of nerve, including TZ, central myelin root portion, & adjacent brainstem surface
- Glossopharyngeal neuralgia caused by neurovascular compression: 95% in proximal REZ, overlapping proximal location of TZ
- Travels anterolaterally through basal cistern with vagus nerve & bulbar portion of accessory nerve
- Passes through glossopharyngeal meatus into **pars nervosa** portion of **jugular foramen**
- ### Skull Base Segment
- Passes through anterior **pars nervosa**
- Accompanied by inferior petrosal sinus
- CNX & CNXI posteriorly within pars vascularis portion of jugular foramen
- Superior & inferior sensory ganglia of CNIX found within jugular foramen
- ### Extracranial Segment
- Exits into anterior **nasopharyngeal carotid space**
- Passes lateral to internal carotid artery, innervates stylopharyngeus, & contributes to carotid sinus nerve
- Gives branches to pharyngeal plexus & terminates as tonsillar & lingual branches
- ### Extracranial Branches
- **Tympanic branch (Jacobson nerve)**
- Sensation from middle ear & parasympathetic to parotid gland via lesser petrosal nerve & otic ganglion
- Arises from inferior sensory ganglion in jugular foramen
- Via**inferior tympanic canaliculus** to hypotympanum
- Aberrant internal carotid artery enters via this canal
- Forms tympanic plexus on cochlear promontory
- Associated glomus bodies form glomus tympanicum paraganglioma
- **Stylopharyngeus branch**
- Motor to stylopharyngeus muscle; arises from CNIX between stylopharyngeus & styloglossus muscles
- **Carotid sinus nerve**
- Supplies viscerosensory fibers to carotid sinus & body
- Conducts impulses from mechanoreceptors of sinus & chemoreceptors of carotid body to medulla
- **Pharyngeal branches**
- Sensory input from posterior oropharynx & soft palate (pharyngeal plexus)
- **Lingual branch**
- Sensory input & taste from posterior 1/3 of tongue
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- MR imaging method of choice
- Superior sensitivity for skull base, meningeal, cisternal, & brainstem pathology
- T2 (including 3D high-resolution, heavily T2-weighted), T1 without fat saturation, & contrast-enhanced T1 sequences with fat saturation in axial & coronal planes
- Supplemental bone CT for complex skull base pathology
- ### Imaging Sweet Spots
- Image from pontomedullary junction to hyoid bone
- CNIX nuclei & intraaxial segment not directly visualized
- Position inferred by identifying upper medulla, posterior to postolivary sulcus
- Cisternal segment not always visualized on routine MR
- High-resolution thin-section T2 sequences often identify cisternal segments of CNIX-XI nerve complex
- Bone algorithm CT for bony anatomy of pars nervosa
- Extracranial segment not visualized
- ### Imaging Pitfalls
- Remember to image entire extracranial course of CNIX beyond skull base
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Complex CNIX-XI neuropathies (Vernet syndrome) caused by disease in medulla, basal cistern, jugular foramen, or nasopharyngeal carotid space
- Isolated CNIX neuropathy exceedingly rare
- Glossopharyngeal neuralgia mostly from compression by PICA > vertebral > AICA; minority from trauma, neoplasm, infection, multiple sclerosis, or elongated styloid process (Eagle syndrome)
e0170af1-68fd-47ec-9f6a-c6951287feff
## Images
### Graphics
![Posterior view of the brainstem emphasizes the 4 nuclei participating in the functions of the glossopharyngeal nerve. Notice the 2 efferent nuclei, the nucleus ambiguus and inferior salivatory nucleus labeled on the right. The nucleus ambiguus supplies motor fibers to the stylopharyngeus muscle, while the inferior salivatory nucleus supplies parasympathetic fibers to the parotid gland. On the left, the afferent nuclei are the solitary tract nucleus and the spinal nucleus of CNV. The solitary tract nucleus receives taste fibers from the tongue base, while the spinal nucleus of CNV receives sensation from the middle ear, soft palate, tongue base, and pharynx.](images/app.statdx.com_image_thumbnail_0568113e-ccf1-462c-a4f2-6c6f3b17a483_annotated_false_size_900_quality_90_0a3c1435bed7c2ee1dc18fe82e128a903ed3715b.jpg)
*Posterior view of the brainstem emphasizes the 4 nuclei participating in the functions of the glossopharyngeal nerve. Notice the 2 efferent nuclei, the nucleus ambiguus and inferior salivatory nucleus labeled on the right. The nucleus ambiguus supplies motor fibers to the stylopharyngeus muscle, while the inferior salivatory nucleus supplies parasympathetic fibers to the parotid gland. On the left, the afferent nuclei are the solitary tract nucleus and the spinal nucleus of CNV. The solitary tract nucleus receives taste fibers from the tongue base, while the spinal nucleus of CNV receives sensation from the middle ear, soft palate, tongue base, and pharynx.*
![Posterior view of the brainstem emphasizes the 4 nuclei participating in the functions of the glossopharyngeal nerve. Notice the 2 efferent nuclei, the nucleus ambiguus and inferior salivatory nucleus labeled on the right. The nucleus ambiguus supplies motor fibers to the stylopharyngeus muscle, while the inferior salivatory nucleus supplies parasympathetic fibers to the parotid gland. On the left, the afferent nuclei are the solitary tract nucleus and the spinal nucleus of CNV. The solitary tract nucleus receives taste fibers from the tongue base, while the spinal nucleus of CNV receives sensation from the middle ear, soft palate, tongue base, and pharynx.](images/app.statdx.com_image_thumbnail_0568113e-ccf1-462c-a4f2-6c6f3b17a483_size_174_quality_85_38559753_20251018T124943Z.jpg)
*Posterior view of the brainstem emphasizes the 4 nuclei participating in the functions of the glossopharyngeal nerve. Notice the 2 efferent nuclei, the nucleus ambiguus and inferior salivatory nucleus labeled on the right. The nucleus ambiguus supplies motor fibers to the stylopharyngeus muscle, while the inferior salivatory nucleus supplies parasympathetic fibers to the parotid gland. On the left, the afferent nuclei are the solitary tract nucleus and the spinal nucleus of CNV. The solitary tract nucleus receives taste fibers from the tongue base, while the spinal nucleus of CNV receives sensation from the middle ear, soft palate, tongue base, and pharynx.*
![Posterior view of the brainstem emphasizes the 4 nuclei participating in the functions of the glossopharyngeal nerve. Notice the 2 efferent nuclei, the nucleus ambiguus and inferior salivatory nucleus labeled on the right. The nucleus ambiguus supplies motor fibers to the stylopharyngeus muscle, while the inferior salivatory nucleus supplies parasympathetic fibers to the parotid gland. On the left, the afferent nuclei are the solitary tract nucleus and the spinal nucleus of CNV. The solitary tract nucleus receives taste fibers from the tongue base, while the spinal nucleus of CNV receives sensation from the middle ear, soft palate, tongue base, and pharynx.](images/app.statdx.com_image_thumbnail_0568113e-ccf1-462c-a4f2-6c6f3b17a483_size_174_quality_85_4e3e42657f6483099059da67dbc0e8a814ce0b61.jpg)
*Posterior view of the brainstem emphasizes the 4 nuclei participating in the functions of the glossopharyngeal nerve. Notice the 2 efferent nuclei, the nucleus ambiguus and inferior salivatory nucleus labeled on the right. The nucleus ambiguus supplies motor fibers to the stylopharyngeus muscle, while the inferior salivatory nucleus supplies parasympathetic fibers to the parotid gland. On the left, the afferent nuclei are the solitary tract nucleus and the spinal nucleus of CNV. The solitary tract nucleus receives taste fibers from the tongue base, while the spinal nucleus of CNV receives sensation from the middle ear, soft palate, tongue base, and pharynx.*
![Axial graphic through the medullary brainstem from above shows the 4 nuclei of the glossopharyngeal nerve.](images/app.statdx.com_image_thumbnail_23c03cd1-bb67-49d9-9c91-b79d7ab0e93b_annotated_false_size_900_quality_90_2e1c3b59de0a130e9f6528932612f55d2e5540db.jpg)
*Axial graphic through the medullary brainstem from above shows the 4 nuclei of the glossopharyngeal nerve.*
### Graphic, Extracranial
![Graphic of the skull base viewed from below depicts the 4 cranial nerves emerging into the nasopharyngeal carotid space. The glossopharyngeal nerve is just anteromedial to the internal jugular vein as it exits the pars nervosa of the jugular foramen.](images/app.statdx.com_image_thumbnail_5279ce95-b312-4313-92a5-f3dbe5bd7974_annotated_false_size_900_quality_90_0ac0921f855af78e197f0a4b94179626e69bb356.jpg)
*Graphic of the skull base viewed from below depicts the 4 cranial nerves emerging into the nasopharyngeal carotid space. The glossopharyngeal nerve is just anteromedial to the internal jugular vein as it exits the pars nervosa of the jugular foramen.*
![Axial graphic of nasopharyngeal carotid spaces shows the extracranial glossopharyngeal nerve situated anteriorly in the gap between the internal carotid artery and the internal jugular vein. Notice that at this level, CNX, CNXI, and CNXII are all still within the carotid space. The glossopharyngeal nerve exits the carotid space at the level of the high oropharynx.](images/app.statdx.com_image_thumbnail_a9a15253-1309-49e3-a307-3bf79325f9be_annotated_false_size_900_quality_90_3e9d07f908170f39cc1b1ae67cc0f88582f425f4.jpg)
*Axial graphic of nasopharyngeal carotid spaces shows the extracranial glossopharyngeal nerve situated anteriorly in the gap between the internal carotid artery and the internal jugular vein. Notice that at this level, CNX, CNXI, and CNXII are all still within the carotid space. The glossopharyngeal nerve exits the carotid space at the level of the high oropharynx.*
![Sagittal graphic emphasizing the extracranial component of the glossopharyngeal nerve (CNIX) is shown. Only 1 muscle is innervated by the fibers in CNIX from the nucleus ambiguus, the stylopharyngeus. Sensory information from the middle ear, tongue base, soft palate, and oropharyngeal surface are transmitted via CNIX to the spinal nucleus of the trigeminal nerve. Taste sensation from the tongue base travels via CNIX to the solitary tract nucleus. Parasympathetic secretomotor fibers from the inferior salivatory nucleus bound for the parotid gland also travel in CNIX.](images/app.statdx.com_image_thumbnail_9465fd18-ad4c-415e-b651-3287f9e697a5_annotated_false_size_900_quality_90_bd648e81bc1281ec7cd205dc820eff85662695e2.jpg)
*Sagittal graphic emphasizing the extracranial component of the glossopharyngeal nerve (CNIX) is shown. Only 1 muscle is innervated by the fibers in CNIX from the nucleus ambiguus, the stylopharyngeus. Sensory information from the middle ear, tongue base, soft palate, and oropharyngeal surface are transmitted via CNIX to the spinal nucleus of the trigeminal nerve. Taste sensation from the tongue base travels via CNIX to the solitary tract nucleus. Parasympathetic secretomotor fibers from the inferior salivatory nucleus bound for the parotid gland also travel in CNIX.*
### Axial Bone CT
![First of 3 axial bone CT images presented from inferior to superior through the posterior skull base emphasizes the bony anatomy of the jugular foramen. The jugular foramen is located on the floor of the posterior cranial fossa between the petrous temporal bone anterolaterally and occipital bone posteromedially; therefore, it is a venous channel between these bones.](images/app.statdx.com_image_thumbnail_c384e838-0394-4223-87e3-21a35801aef4_annotated_false_size_900_quality_90_417259f7bd222ca8ae38c95030cafee79257f303.jpg)
*First of 3 axial bone CT images presented from inferior to superior through the posterior skull base emphasizes the bony anatomy of the jugular foramen. The jugular foramen is located on the floor of the posterior cranial fossa between the petrous temporal bone anterolaterally and occipital bone posteromedially; therefore, it is a venous channel between these bones.*
![The jugular foramen is seen here as 2 discrete pieces, the smaller anteromedial pars nervosa and larger posterolateral pars vascularis, separated by the jugular spine of the petrous bone.](a6ab915c-ecce-4c75-a3c1-f5ef8a306709)
*The jugular foramen is seen here as 2 discrete pieces, the smaller anteromedial pars nervosa and larger posterolateral pars vascularis, separated by the jugular spine of the petrous bone.*
![The 2 parts of the jugular foramen are visibile. The pars nervosa transmits the glossopharyngeal nerve (CNIX), Jacobson nerve, and inferior petrosal sinus. The pars vascularis transmits the vagus (CNX) and accessory (CNXI) cranial nerves, Arnold nerve, and sigmoid sinus, which becomes the internal jugular vein.](a0742797-ad55-4bcd-b992-58ee444261b6)
*The 2 parts of the jugular foramen are visibile. The pars nervosa transmits the glossopharyngeal nerve (CNIX), Jacobson nerve, and inferior petrosal sinus. The pars vascularis transmits the vagus (CNX) and accessory (CNXI) cranial nerves, Arnold nerve, and sigmoid sinus, which becomes the internal jugular vein.*
### Axial T2 MR
![First of 3 axial high-resolution T2 MR images through the brainstem medulla presented from inferior to superior is shown. The glossopharyngeal nerve is seen passing laterally into the pars nervosa of the jugular foramen.](6f86b537-c934-4608-90de-293d0eb3a6c9)
*First of 3 axial high-resolution T2 MR images through the brainstem medulla presented from inferior to superior is shown. The glossopharyngeal nerve is seen passing laterally into the pars nervosa of the jugular foramen.*
![The glossopharyngeal nerve (CNIX), vagus nerve (CNX), and bulbar accessory nerve (CNXI) all exit the medulla laterally in the postolivary sulcus. CNIX is the most cephalad of these. With routine MR imaging it is not possible to see these 3 cranial nerves individually.](d87f2d7a-1e8c-4b9f-9530-d3fefeab670b)
*The glossopharyngeal nerve (CNIX), vagus nerve (CNX), and bulbar accessory nerve (CNXI) all exit the medulla laterally in the postolivary sulcus. CNIX is the most cephalad of these. With routine MR imaging it is not possible to see these 3 cranial nerves individually.*
![In the upper medulla, the vagus nerve is well seen leaving the brainstem via the postolivary sulcus. The glossopharyngeal nerve is seen more laterally, as it has already exited the brainstem above the vagus nerve.](ea1c45f1-8a51-4838-8eea-a025cdf3cc05)
*In the upper medulla, the vagus nerve is well seen leaving the brainstem via the postolivary sulcus. The glossopharyngeal nerve is seen more laterally, as it has already exited the brainstem above the vagus nerve.*
![First of 4 axial heavily T2-weighted MR images from superior to inferior is shown, demonstrating the right glossopharyngeal nerve (CNIX) exiting the medulla laterally in the postolivary sulcus. A high-resolution 3D heavily T2-weighted sequence, such as CISS, FIESTA, or DRIVE, is key to evaluating these nerves.](d4f308fe-2038-4ced-8d30-9ed8762f8405)
*First of 4 axial heavily T2-weighted MR images from superior to inferior is shown, demonstrating the right glossopharyngeal nerve (CNIX) exiting the medulla laterally in the postolivary sulcus. A high-resolution 3D heavily T2-weighted sequence, such as CISS, FIESTA, or DRIVE, is key to evaluating these nerves.*
![The vagus nerve (CNX) and bulbar accessory nerve (CNXI) also exit the medulla in the postolivary sulcus. CNIX arises cephalad to these. This image demonstrates the right vagus nerve arising from the brainstem via the postolivary sulcus. The cisternal segment of the right CNIX is seen more laterally, as it already exited the brainstem above the vagus nerve.](d74e4040-7c60-4517-98b0-9caf518fc531)
*The vagus nerve (CNX) and bulbar accessory nerve (CNXI) also exit the medulla in the postolivary sulcus. CNIX arises cephalad to these. This image demonstrates the right vagus nerve arising from the brainstem via the postolivary sulcus. The cisternal segment of the right CNIX is seen more laterally, as it already exited the brainstem above the vagus nerve.*
![Axial T2-weighted MR in the same patient shows the right CNIX entering the pars nervosa of the jugular foramen.](92fb794b-0f8a-43c9-9787-f35b8177b9ac)
*Axial T2-weighted MR in the same patient shows the right CNIX entering the pars nervosa of the jugular foramen.*
### Axial and coronal T2 MR
![MR in another patient demonstrates the course of the right glossopharyngeal nerve (CNIX) in the cistern entering the pars nervosa of the jugular foramen. The vagus nerve (CNX) and accessory nerve (CNXI) are both seen on the left side.](e1fde9ca-476e-4e9c-b8b9-bcdbf6c70a96)
*MR in another patient demonstrates the course of the right glossopharyngeal nerve (CNIX) in the cistern entering the pars nervosa of the jugular foramen. The vagus nerve (CNX) and accessory nerve (CNXI) are both seen on the left side.*
![Coronal reformat from a 3D heavily T2-weighted MR demonstrates the cisternal segments of the right CNIX, CNX, and CNXI as they enter the jugular foramen on the right. The segments may not always be as clearly visualized, as they are not on the left side in this image.](6fab5650-4e35-40eb-8fb1-208c17caaf37)
*Coronal reformat from a 3D heavily T2-weighted MR demonstrates the cisternal segments of the right CNIX, CNX, and CNXI as they enter the jugular foramen on the right. The segments may not always be as clearly visualized, as they are not on the left side in this image.*
![Oblique coronal reformat from a 3D heavily T2-weighted MR shows the cisternal segments of CNIX, CNX, and CNXI as they enter the jugular foramen on the right. CNIX enters the jugular foramen through the glossopharyngeal meatus, whereas CNX and CNXI enter through the vagal meatus, and the fibers of CNX and CNXI intermix with each other within the jugular foramen and are classified together as the CNX/XI complex.](5f7aa168-f44e-4f77-967b-1b75f54bb0e2)
*Oblique coronal reformat from a 3D heavily T2-weighted MR shows the cisternal segments of CNIX, CNX, and CNXI as they enter the jugular foramen on the right. CNIX enters the jugular foramen through the glossopharyngeal meatus, whereas CNX and CNXI enter through the vagal meatus, and the fibers of CNX and CNXI intermix with each other within the jugular foramen and are classified together as the CNX/XI complex.*
docs_md/articles/cnv-trigeminal-nerve_9db87cfa-58ff-45fd-a7fd-fe8c73eb9770.md
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## TERMINOLOGY
- ### Abbreviations
- Trigeminal nerve (CNV)
- Ophthalmic division, trigeminal nerve: CNV1
- Maxillary division, trigeminal nerve: CNV2
- Mandibular division, trigeminal nerve: CNV3
- ### Synonyms
- CN5
- ### Definitions
- CNV: Great sensory cranial nerve of head and face; motor nerve for muscles of mastication
## IMAGING ANATOMY
- ### Overview
- Mixed nerve (both sensory, motor components)
- 4 segments: Intraaxial, cisternal (preganglionic), intradural (Meckel cave), and extracranial
- ### Intraaxial Segment
- 4 nuclei (3 sensory, 1 motor) in brainstem, upper cord
- **Mesencephalic nucleus CNV**
- Project cephalad from pons to inferior colliculus level
- Slender column of cells
- Found anterior to upper 4th ventricle/aqueduct near lateral margin of central gray matter
- Afferent fibers for **facial proprioception** (teeth, hard palate, and TMJ)
- Sickle-shaped tract descending to motor nucleus
- Controls **mastication** and **bite force**
- **Main sensory nucleus CNV**
- Nucleus lies lateral to entering trigeminal root
- Provides **facial tactile sensation**
- **Motor nucleus CNV**
- Anteromedial to principal sensory nucleus
- Ovoid column of cells
- Supplies **muscles of mastication** (pterygoids, masseter, temporalis), tensor tympani, tensor veli palatini (TVP), mylohyoid, anterior belly of digastric
- **Spinal nucleus CNV**
- Extends from principal sensory root in pons into upper cervical cord (between C2 to C4 level)
- Conveys **facial pain, temperature**
- ### Cisternal (Preganglionic) Segment
- Roots: Smaller motor (1, 2, or 3), larger sensory
- Emerges from lateral pons at **root entry zone** (REZ)
- Courses anterosuperiorly through prepontine cistern
- Enters middle cranial fossa by passing beneath tentorium at apex of petrous temporal bone
- Passes through opening in dura matter called **porus trigeminus** to enter Meckel cave
- ### Intradural Segment
- **Meckel cave** formed by meningeal layer of dura lined by arachnoid; pia covers CNV in trigeminal cave
- Cave filled with CSF (90%) and continuous with prepontine subarachnoid space
- Preganglionic CNV ends at **trigeminal ganglion** (TG)
- TG: Crescentic, located in anteroinferior Meckel cave
- TG synonyms: **Gasserian**or**semilunar ganglion**
- TG lacks blood-nerve barrier, enhances with contrast
- ### Divisions (Postganglionic) of CNV
- **Ophthalmic nerve (CNV1)**: Courses in cavernous sinus
- Courses in lateral cavernous sinus wall below CNIV
- Exits skull through superior orbital fissure, enters orbit
- Divides into lacrimal, frontal, and nasociliary nerves
- Sensory innervation of **scalp, forehead, nose, globe**
- **Maxillary nerve (CNV2)**: Courses in cavernous sinus
- Courses in lateral cavernous sinus wall below CNV1
- Largest nerve in pterygopalatine fossa (PPF), enters posterosuperolateral PPF from cavernous sinus lateral wall in middle cranial fossa through **foramen rotundum**
- Provides sensory innervation to cheek, maxillary sinus, nasal cavity, maxillary alveolar ridge, palate and posterior wall of nasopharynx
- CNV2 passes anteriorly and laterally through **upper aspect of PPF** giving rise to zygomatic nerve and posterior superior alveolar nerves
- Continues anteriorly along roof of PPF into **inferior orbital fissure (IOF)**, gives rise to anterior and middle superior alveolar nerve branches
- Then enters infraorbital canal in floor of orbit to become **infraorbital nerve**(terminal branch of CNV2)
- CNV2 inferior branches passing through pterygopalatine ganglion in PPF: Greater and lesser palatine nerves
- Nasopalatine (long sphenopalatine) nerve and posterior superior nasal nerve: Exit PPF medially through sphenopalatine foramen
- Greater palatine nerve and lesser palatine nerves: Exit PPF inferiorly through pterygopalatine (greater palatine) canal
- Greater palatine nerve gives rise to lateral posterior inferior nasal nerves within pterygopalatine canal that pass through tiny palatine bony canals to supply middle and inferior nasal meatuses and inferior turbinate
- Greater palatine nerve provides sensory and parasympathetic fibers to ipsilateral gums, mucous membrane and glands of hard palate, and communicates anteriorly with terminal filaments of nasopalatine nerve
- Lesser palatine nerves supply soft palate, uvula, and tonsil
- Pharyngeal nerve: Exits PPF posteroinferomedially through palatovaginal canal
- **Mandibular nerve (CNV3)**: Does not enter cavernous sinus
- Exits directly from Meckel cave, passing inferiorly through foramen ovale into **masticator space**(MS)
- Carries both motor and sensory fibers; motor root bypasses TG, joins CNV3 as it exits via **foramen ovale**
- Located near skull base medial to lateral pterygoid (LP) and lateral to TVP muscle, within**trigeminal fat pad**
- **Otic ganglion (OG**): Below skull base between CNV3 and TVP
- **Lesser petrosal nerve** (branch of tympanic plexus formed by tympanic branch of glossopharyngeal nerve) provides preganglionic parasympathetic supply to OG from medullary inferior salivatory nucleus
- Lesser petrosal nerve exits middle cranial fossa via foramen ovale, or, occasionally, via separate foramen called "**canaliculus innominatus**"
- Nonrelaying sympathetic root to otic ganglion (OG) from plexus on middle meningeal artery (MMA)
- OG postganglionic secretomotor fibers to parotid join auriculotemporal nerve (CNV3 branch)
- **Main trunk of CNV3** gives off meningeal branch and nerve to medial pterygoid (MP); latter provides nonrelaying motor root to OG, which supplies TVP and tensor tympani muscles
- Main trunk soon divides into small**anterior division** and large**posterior division**
- Anterior division: Masseteric nerve, 2 deep temporal nerves and nerve to LP motor branches, and buccal nerve sensory branch
- **Auriculotemporal nerve** arises from 2 roots of proximal posterior division → runs backward, encircling MMA and forms single trunk → again backward, ascending behind neck of mandible above internal maxillary artery → ascends on temple behind superficial temporal vessels
- Sensory to external ear, TMJ, parotid, temple and secretomotor to parotid via OG
- Posterior division then divides into terminal branches: Inferior alveolar (posterior) and lingual (anterior) nerves
- **Inferior alveolar nerve**(sensory to mandible and chin) runs downward lateral to MP → enters mandibular foramen (gives off **mylohyoid nerve**just before entering mandible) → runs in mandibular canal → finally emerges at mental foramen as mental nerve
- Mylohyoid nerve (motor to anterior belly of digastric and mylohyoid muscles) contains all motor fibers of posterior division of CNV3
- **Lingual nerve** (CNV3 sensory to anterior 2/3 tongue, floor of mouth) begins 1 cm below skull → runs 1st between TVP and LP → then between LP and MP → then runs anteroinferiorly between MP and mandibular ramus → then runs in direct contact with mandible medial to 3rd molar tooth → finally in lateral sublingual space compartment
- **Chorda tympani nerve**(CT, CNVII branch) distributed through lingual nerve joins lingual nerve in MS 2 cm below skull base after exiting petrotympanic fissure
- CT: Anterior 2/3 tongue taste; and secretomotor to submandibular/sublingual salivary glands via its preganglionic parasympathetic supply from pontine superior salivatory nucleus to submandibular ganglion
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- CT best for skull base and bony foramina
- 3D T2 MR for intraaxial, cisternal, and intradural segments
- T1 C+ fat-saturated MR of entire extracranial course
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Sensory complaints: Pain, burning, numbness in face
- Motor (V3 only): Weakness in chewing
- Proximal V3 injury causes motor atrophy of masticator muscles within 6 weeks to 3 months
- Distal V3 injury (above mylohyoid nerve takeoff) affects only anterior belly of digastric and mylohyoid
- Tic douloureux (trigeminal neuralgia)
- Sharp, excruciating pain in V2-V3 distributions
30782f93-e073-4e36-a2cc-34589cd4a636
## Images
### Graphics
![Sagittal graphic shows the 4 nuclei of the trigeminal nerve (CNV). From superior to inferior, note the mesencephalic nucleus in the midbrain, the motor nucleus and main sensory nucleus in the pons, and the spinal nucleus extending from the lower pons into the upper cervical spinal cord. The motor root of CNV sends fibers along the mandibular division only.](images/app.statdx.com_image_thumbnail_481e5d2e-c742-4de8-9cea-ce670597b459_annotated_false_size_900_quality_90_745b2f51198726b47fddbd5f54bf96d922a7c084.jpg)
*Sagittal graphic shows the 4 nuclei of the trigeminal nerve (CNV). From superior to inferior, note the mesencephalic nucleus in the midbrain, the motor nucleus and main sensory nucleus in the pons, and the spinal nucleus extending from the lower pons into the upper cervical spinal cord. The motor root of CNV sends fibers along the mandibular division only.*
![Sagittal graphic shows the 4 nuclei of the trigeminal nerve (CNV). From superior to inferior, note the mesencephalic nucleus in the midbrain, the motor nucleus and main sensory nucleus in the pons, and the spinal nucleus extending from the lower pons into the upper cervical spinal cord. The motor root of CNV sends fibers along the mandibular division only.](images/app.statdx.com_image_thumbnail_481e5d2e-c742-4de8-9cea-ce670597b459_size_174_quality_85_cb91f3801fb39d13347226917607cc73ff932f34.jpg)
*Sagittal graphic shows the 4 nuclei of the trigeminal nerve (CNV). From superior to inferior, note the mesencephalic nucleus in the midbrain, the motor nucleus and main sensory nucleus in the pons, and the spinal nucleus extending from the lower pons into the upper cervical spinal cord. The motor root of CNV sends fibers along the mandibular division only.*
![Axial graphic depicts CNV course from pontine nuclei (main sensory and motor nuclei) to the 3 main branches (CNV1, CNV2, CNV3). Notice the large preganglionic segment entering the lateral pons at the root entry/exit zone (REZ). It then enters the Meckel cave through the porus trigeminus to become the trigeminal ganglion. Vascular loop compression of the transition zone (TZ) between central and peripheral myelin is the most common cause of trigeminal neuralgia, most commonly by the superior cerebellar artery. The term REZ is often synonymously used for TZ, but REZ is actually the part of nerve that includes the TZ, central myelin root portion, and adjacent surface of the brainstem. TZ is the vulnerable anatomic area for neurovascular compression symptoms and is not always in the same position as REZ.](images/app.statdx.com_image_thumbnail_4fe1f499-b882-40e1-b7fc-55e812565e30_annotated_false_size_900_quality_90_060904f29ec2f9ac88b8c3b8ab3872e5de6ec7fb.jpg)
*Axial graphic depicts CNV course from pontine nuclei (main sensory and motor nuclei) to the 3 main branches (CNV1, CNV2, CNV3). Notice the large preganglionic segment entering the lateral pons at the root entry/exit zone (REZ). It then enters the Meckel cave through the porus trigeminus to become the trigeminal ganglion. Vascular loop compression of the transition zone (TZ) between central and peripheral myelin is the most common cause of trigeminal neuralgia, most commonly by the superior cerebellar artery. The term REZ is often synonymously used for TZ, but REZ is actually the part of nerve that includes the TZ, central myelin root portion, and adjacent surface of the brainstem. TZ is the vulnerable anatomic area for neurovascular compression symptoms and is not always in the same position as REZ.*
![Coronal graphic shows the mandibular division of the trigeminal nerve (CNV3), which exits directly from the Meckel cave, passing inferiorly through the foramen ovale into the masticator space and never entering the cavernous sinus. Meckel cave is actually a small anterior extension (pseudopod) of the lateral prepontine cistern, containing both the trigeminal nerve rootlets and trigeminal ganglion. Remember: CNV3 possesses the motor fibers of the trigeminal nerve. Main trunk of CNV3 gives off a motor nerve to medial pterygoid, which also supplies tensor veli palatini and tensor tympani via the otic ganglion. Anterior division of main trunk gives rise to masseteric nerve, 2 deep temporal nerves, and nerve to lateral pterygoid motor branches. Mylohyoid nerve (motor to anterior belly of digastric and mylohyoid muscles) arises from inferior alveolar nerve and contains all motor fibers of posterior division of CNV3.](images/app.statdx.com_image_thumbnail_7c1aca9e-5042-44ba-accc-b0ebb0871add_annotated_false_size_900_quality_90_483a34725c641f328c8ef825d529cc482dab4d7a.jpg)
*Coronal graphic shows the mandibular division of the trigeminal nerve (CNV3), which exits directly from the Meckel cave, passing inferiorly through the foramen ovale into the masticator space and never entering the cavernous sinus. Meckel cave is actually a small anterior extension (pseudopod) of the lateral prepontine cistern, containing both the trigeminal nerve rootlets and trigeminal ganglion. Remember: CNV3 possesses the motor fibers of the trigeminal nerve. Main trunk of CNV3 gives off a motor nerve to medial pterygoid, which also supplies tensor veli palatini and tensor tympani via the otic ganglion. Anterior division of main trunk gives rise to masseteric nerve, 2 deep temporal nerves, and nerve to lateral pterygoid motor branches. Mylohyoid nerve (motor to anterior belly of digastric and mylohyoid muscles) arises from inferior alveolar nerve and contains all motor fibers of posterior division of CNV3.*
![Coronal graphic through cavernous sinus shows CNV2 in the lateral wall of the cavernous sinus, just inferior to CNV1. CNV1, CNIII, and CNIV are all embedded in the lateral wall of cavernous sinus. The only centrally located intracavernous cranial nerve is abducens nerve (CNVI).](images/app.statdx.com_image_thumbnail_0e6bdfdc-108c-4408-bf47-7860abd8cc07_annotated_false_size_900_quality_90_b446fc176a2adc40c5dead50f43746721ed1ba31.jpg)
*Coronal graphic through cavernous sinus shows CNV2 in the lateral wall of the cavernous sinus, just inferior to CNV1. CNV1, CNIII, and CNIV are all embedded in the lateral wall of cavernous sinus. The only centrally located intracavernous cranial nerve is abducens nerve (CNVI).*
![Graphic of CNV shows major branches. Ophthalmic division (CNV1) enters orbit via superior orbital fissure, dividing into frontal, nasociliary, and lacrimal branches. Maxillary division (CNV2) enters pterygopalatine fossa via foramen rotundum, gives off multiple branches, continues into inferior orbital fissure and infraorbital canal, and terminates as infraorbital nerve. Mandibular division exits via foramen ovale. Otic ganglion (OG) lies just below skull base between CNV3 and tensor veli palatini muscle. Lesser petrosal nerve gives preganglionic parasympathetics to OG from medullary inferior salivatory nucleus, and sympathetic root is from plexus on middle meningeal artery. Postganglionic secretomotor fibers for parotid gland join auriculotemporal nerve (CNV3 branch).](images/app.statdx.com_image_thumbnail_5f50a71e-5494-45f7-af55-ea6b2c8d78ec_annotated_false_size_900_quality_90_dd1ec63585a2ecc65cc851a25f1520293c40c367.jpg)
*Graphic of CNV shows major branches. Ophthalmic division (CNV1) enters orbit via superior orbital fissure, dividing into frontal, nasociliary, and lacrimal branches. Maxillary division (CNV2) enters pterygopalatine fossa via foramen rotundum, gives off multiple branches, continues into inferior orbital fissure and infraorbital canal, and terminates as infraorbital nerve. Mandibular division exits via foramen ovale. Otic ganglion (OG) lies just below skull base between CNV3 and tensor veli palatini muscle. Lesser petrosal nerve gives preganglionic parasympathetics to OG from medullary inferior salivatory nucleus, and sympathetic root is from plexus on middle meningeal artery. Postganglionic secretomotor fibers for parotid gland join auriculotemporal nerve (CNV3 branch).*
![Graphic shows CNV3 exiting skull through foramen ovale without entering cavernous sinus. Main trunk gives off meningeal branch and nerve to medial pterygoid, soon dividing into small anterior division (giving rise to other masticator muscle branches and buccal sensory branch) and large posterior division, giving rise to auriculotemporal, inferior alveolar (gives off mylohyoid nerve), and lingual nerves.](d6a3bad5-bb1d-4480-9262-8c5b04b16d89)
*Graphic shows CNV3 exiting skull through foramen ovale without entering cavernous sinus. Main trunk gives off meningeal branch and nerve to medial pterygoid, soon dividing into small anterior division (giving rise to other masticator muscle branches and buccal sensory branch) and large posterior division, giving rise to auriculotemporal, inferior alveolar (gives off mylohyoid nerve), and lingual nerves.*
### Axial Bone CT
![First of 3 axial bone CT images from inferior to superior through central skull base is shown. CNV2 exits the skull base through the foramen rotundum to enter the superior margin of the pterygopalatine fossa. CNV3 exits via the foramen ovale to enter the masticator space, where it supplies motor innervation to muscles of mastication and sensory sensory innervation through inferior alveolar, lingual, and auriculotemporal nerves. Note adjacent foramen spinosum, which contains middle meningeal artery, vein, and meningeal branch of CNV3. Lesser petrosal nerve exits the middle cranial fossa via the foramen ovale, or, occasionally, via a tiny &quot;canaliculus innominatus&quot; in between and medial to foramen ovale and spinosum.](b0be103c-a2b0-4bf5-82f3-17860ff51bfa)
*First of 3 axial bone CT images from inferior to superior through central skull base is shown. CNV2 exits the skull base through the foramen rotundum to enter the superior margin of the pterygopalatine fossa. CNV3 exits via the foramen ovale to enter the masticator space, where it supplies motor innervation to muscles of mastication and sensory sensory innervation through inferior alveolar, lingual, and auriculotemporal nerves. Note adjacent foramen spinosum, which contains middle meningeal artery, vein, and meningeal branch of CNV3. Lesser petrosal nerve exits the middle cranial fossa via the foramen ovale, or, occasionally, via a tiny &quot;canaliculus innominatus&quot; in between and medial to foramen ovale and spinosum.*
![Foramen ovale (CNV3) and foramen rotundum (CNV2) are now best seen on the patient's left. The left foramen rotundum is seen opening into the superior pterygopalatine fossa.](547e4550-7ca1-49ec-ac4d-24168428a489)
*Foramen ovale (CNV3) and foramen rotundum (CNV2) are now best seen on the patient's left. The left foramen rotundum is seen opening into the superior pterygopalatine fossa.*
![Superior orbital fissure transmits the ophthalmic division of CNV from cranium to orbit. Other structures passing through the superior orbital fissure include the oculomotor nerve (CNIII), trochlear nerve (CNIV), abducens nerve (CNVI), and the superior ophthalmic vein.](57fbbffa-911d-4688-a6eb-bd3339f94bab)
*Superior orbital fissure transmits the ophthalmic division of CNV from cranium to orbit. Other structures passing through the superior orbital fissure include the oculomotor nerve (CNIII), trochlear nerve (CNIV), abducens nerve (CNVI), and the superior ophthalmic vein.*
### Axial T2 MR
![First of 3 axial T2 MR images through CNV and the Meckel cave presented from inferior to superior shows a layer of hypointense dura mater forming the lateral wall and the roof of the Meckel cave. The right abducens nerve is seen penetrating dura to enter the Dorello canal. CNV fascicles can be seen with CSF of the Meckel cave.](36172bcd-fd28-4ede-9ca8-4f48a516b3c6)
*First of 3 axial T2 MR images through CNV and the Meckel cave presented from inferior to superior shows a layer of hypointense dura mater forming the lateral wall and the roof of the Meckel cave. The right abducens nerve is seen penetrating dura to enter the Dorello canal. CNV fascicles can be seen with CSF of the Meckel cave.*
![Preganglionic fascicles of CNV are seen within the Meckel cave, which contains CSF, trigeminal fascicles, and trigeminal ganglion. Note main sensory and motor nuclei locations.](2825913c-a93a-4cf3-b7da-f4e53fd21640)
*Preganglionic fascicles of CNV are seen within the Meckel cave, which contains CSF, trigeminal fascicles, and trigeminal ganglion. Note main sensory and motor nuclei locations.*
![In this image, the preganglionic segment of CNV is seen spanning the distance between the REZ on the lateral pons and the porus trigeminus of the Meckel cave. REZ is actually the part of nerve that includes the TZ between central and peripheral myelin, central myelin root portion, and adjacent surface of the brainstem. TZ is the vulnerable anatomic area for neurovascular compression symptoms. The cisternal portion measures ~ 8-15 mm in length, and the zone with central myelin (which is the distance from the brainstem to TZ) is shorter on the medial side (1.13 mm) than on the lateral side (2.47 mm) of the nerve.](d12144e0-bc44-4d4b-a5c5-7d367098cce2)
*In this image, the preganglionic segment of CNV is seen spanning the distance between the REZ on the lateral pons and the porus trigeminus of the Meckel cave. REZ is actually the part of nerve that includes the TZ between central and peripheral myelin, central myelin root portion, and adjacent surface of the brainstem. TZ is the vulnerable anatomic area for neurovascular compression symptoms. The cisternal portion measures ~ 8-15 mm in length, and the zone with central myelin (which is the distance from the brainstem to TZ) is shorter on the medial side (1.13 mm) than on the lateral side (2.47 mm) of the nerve.*
### Axial T1 C+ MR
![First of 3 axial T1 C+ FS MR images presented from inferior to superior through the central skull base shows the right maxillary nerve (CNV2) passing anteriorly into the foramen rotundum and the left mandibular nerve (CNV3) passing inferiorly through the foramen ovale. Both nerves are surrounded by enhancing veins communicating with the extracranial venous system. The foramen rotundum connects the lateral wall of the cavernous sinus in the medial aspect of the middle cranial fossa with the posterosuperolateral aspect of the pterygopalatine fossa. The foramen ovale connects the middle cranial fossa floor with the masticator space.](a2a416d3-0381-4b57-8afb-8bc8c8b106e2)
*First of 3 axial T1 C+ FS MR images presented from inferior to superior through the central skull base shows the right maxillary nerve (CNV2) passing anteriorly into the foramen rotundum and the left mandibular nerve (CNV3) passing inferiorly through the foramen ovale. Both nerves are surrounded by enhancing veins communicating with the extracranial venous system. The foramen rotundum connects the lateral wall of the cavernous sinus in the medial aspect of the middle cranial fossa with the posterosuperolateral aspect of the pterygopalatine fossa. The foramen ovale connects the middle cranial fossa floor with the masticator space.*
![More superior image demonstrates the ovoid shape of the CSF-filled Meckel cave. The trigeminal ganglion is the linear anteroinferior structure in the Meckel cave. It lacks a blood-nerve barrier and therefore normally enhances with contrast.](b17b96d0-4990-446b-b962-7cfa24aa560e)
*More superior image demonstrates the ovoid shape of the CSF-filled Meckel cave. The trigeminal ganglion is the linear anteroinferior structure in the Meckel cave. It lacks a blood-nerve barrier and therefore normally enhances with contrast.*
![Preganglionic segment of CNV arises from the lateral pons at the REZ. The TZ measures ~ 2 mm in length, and the distalmost part of the TZ is 3.4-5.0 mm away from the brainstem. The right internal carotid artery is tortuous within the cavernous sinus.](0003df06-f935-4c62-80c4-8f74591a1377)
*Preganglionic segment of CNV arises from the lateral pons at the REZ. The TZ measures ~ 2 mm in length, and the distalmost part of the TZ is 3.4-5.0 mm away from the brainstem. The right internal carotid artery is tortuous within the cavernous sinus.*
### Coronal T2 MR
![First of 3 coronal T2 MR images presented from posterior to anterior shows the ovoid preganglionic segment of CNV surrounded by high-signal CSF. The preganglionic segment has just exited the lateral pons REZ area. One (in &gt; 1/2 of patients), 2 (in just above 1/3 of patients) or even 3 (in ~ 1/10 of patients) small motor roots of CNV that exit the pons anterosuperomedial to the REZ of the large sensory root may be seen.](8200836b-6f7a-474f-a6aa-44442b8fb655)
*First of 3 coronal T2 MR images presented from posterior to anterior shows the ovoid preganglionic segment of CNV surrounded by high-signal CSF. The preganglionic segment has just exited the lateral pons REZ area. One (in &gt; 1/2 of patients), 2 (in just above 1/3 of patients) or even 3 (in ~ 1/10 of patients) small motor roots of CNV that exit the pons anterosuperomedial to the REZ of the large sensory root may be seen.*
![This more anterior image through the Meckel cave delineates the trigeminal fascicles of the preganglionic trigeminal nerve. The trigeminal ganglion is visible as a semilunar structure in the floor of the Meckel cave bilaterally.](a3e92bf1-1b4b-42dd-bc08-df594f44b2f2)
*This more anterior image through the Meckel cave delineates the trigeminal fascicles of the preganglionic trigeminal nerve. The trigeminal ganglion is visible as a semilunar structure in the floor of the Meckel cave bilaterally.*
![This image through the anterior cavernous sinus shows the maxillary nerve (CNV2) passing anteriorly within the lateral wall of the cavernous sinus and the mandibular nerve (CNV3) passing inferiorly to its exit point in the skull base (foramen ovale). The maxillary nerve (CNV2) passes anteriorly through the foramen rotundum into the pterygopalatine fossa, gives off many branches, and passes through the inferior orbital fissure into the infraorbital canal, terminating as an infraorbital nerve.](59937174-24da-4f55-b608-60dceb61caa8)
*This image through the anterior cavernous sinus shows the maxillary nerve (CNV2) passing anteriorly within the lateral wall of the cavernous sinus and the mandibular nerve (CNV3) passing inferiorly to its exit point in the skull base (foramen ovale). The maxillary nerve (CNV2) passes anteriorly through the foramen rotundum into the pterygopalatine fossa, gives off many branches, and passes through the inferior orbital fissure into the infraorbital canal, terminating as an infraorbital nerve.*
### Coronal T1 C+ MR
![First of 6 coronal T1 C+ MR images through the cavernous sinus presented from posterior to anterior is shown. The trigeminal ganglion is seen as a crescentic area of enhancement in the floor of the Meckel cave. Trigeminal ganglion enhances because it lacks a blood-nerve barrier.](13fc6bf9-70d9-48bd-84cf-de47d195b902)
*First of 6 coronal T1 C+ MR images through the cavernous sinus presented from posterior to anterior is shown. The trigeminal ganglion is seen as a crescentic area of enhancement in the floor of the Meckel cave. Trigeminal ganglion enhances because it lacks a blood-nerve barrier.*
![In this image through the foramen ovale, the mandibular nerve (CNV3) is visible exiting inferiorly into the masticator space.](ae8cfb61-6457-4923-a842-d5d086108ee5)
*In this image through the foramen ovale, the mandibular nerve (CNV3) is visible exiting inferiorly into the masticator space.*
![In this image, the patient's left foramen ovale and mandibular nerve are seen. The motor branches from CNV3 are to the medial pterygoid, which also supplies the tensor veli palatini and tensor tympani (from the main trunk), the masseteric nerve, 2 deep temporal nerves to the temporalis and the nerve to the lateral pterygoid (from the anterior division), and the mylohyoid nerve, which supplies the mylohyoid and anterior belly of the digastric muscles (branch of inferior alveolar nerve; mylohyoid nerve contains all the motor fibers of posterior division). The main sensory branches are the meningeal branch (from main trunk), buccal nerve (from anterior division), auriculotemporal nerve, and the terminal lingual and inferior alveolar nerves (branches of posterior division).](935a06a4-1277-4ea1-9a8c-6101618e1075)
*In this image, the patient's left foramen ovale and mandibular nerve are seen. The motor branches from CNV3 are to the medial pterygoid, which also supplies the tensor veli palatini and tensor tympani (from the main trunk), the masseteric nerve, 2 deep temporal nerves to the temporalis and the nerve to the lateral pterygoid (from the anterior division), and the mylohyoid nerve, which supplies the mylohyoid and anterior belly of the digastric muscles (branch of inferior alveolar nerve; mylohyoid nerve contains all the motor fibers of posterior division). The main sensory branches are the meningeal branch (from main trunk), buccal nerve (from anterior division), auriculotemporal nerve, and the terminal lingual and inferior alveolar nerves (branches of posterior division).*
![In this MR through the anterior margin of the pituitary gland, the maxillary nerve (CNV2) is well seen bilaterally in the inferolateral wall of the cavernous sinus.](ac67fc7f-450e-4b46-8acb-1836becc5a76)
*In this MR through the anterior margin of the pituitary gland, the maxillary nerve (CNV2) is well seen bilaterally in the inferolateral wall of the cavernous sinus.*
![In this more anterior MR, the maxillary nerves are seen in the inferolateral wall of the cavernous sinus just prior to its entry into the foramen rotundum. Inferomedially, note the vidian canals.](20073b25-f81f-481e-b3e9-ac1f51d3bb46)
*In this more anterior MR, the maxillary nerves are seen in the inferolateral wall of the cavernous sinus just prior to its entry into the foramen rotundum. Inferomedially, note the vidian canals.*
![The maxillary nerve can be seen in the foramen rotundum. Notice also the vidian canal widening on its extracranial side with the vidian nerve visible surrounded by a venous plexus. Vidian nerve is formed in vidian canal by confluence of parasympathetic fibers from greater superficial petrosal nerve (GSPN), which is a branch of facial nerve in the temporal bone anterior genu region, and sympathetic fibers from deep petrosal nerve from the plexus around internal carotid artery. Foramen rotundum is situated at the base of greater wing of sphenoid, superolateral to vidian canal, which lies in the body of sphenoid bone. Practically, identify these foramina on coronal images by their relation (superolateral and inferomedial, respectively) to sphenoid sinus lateral (pterygoid) recess or an imaginary lateral recess.](b032f4b9-a011-4e86-8630-dfe6f7e3c048)
*The maxillary nerve can be seen in the foramen rotundum. Notice also the vidian canal widening on its extracranial side with the vidian nerve visible surrounded by a venous plexus. Vidian nerve is formed in vidian canal by confluence of parasympathetic fibers from greater superficial petrosal nerve (GSPN), which is a branch of facial nerve in the temporal bone anterior genu region, and sympathetic fibers from deep petrosal nerve from the plexus around internal carotid artery. Foramen rotundum is situated at the base of greater wing of sphenoid, superolateral to vidian canal, which lies in the body of sphenoid bone. Practically, identify these foramina on coronal images by their relation (superolateral and inferomedial, respectively) to sphenoid sinus lateral (pterygoid) recess or an imaginary lateral recess.*
### Sagittal T2 and Axial T1 MR
![Sagittal T2 MR along the line of the proximal trigeminal nerve shows the preganglionic segment between the REZ in the lateral pons and the trigeminal ganglion in the anteroinferior Meckel cave. The CSF within the Meckel cave communicates with the prepontine cistern through the porus trigeminus.](35d91617-afbe-4693-9775-72cb3d503360)
*Sagittal T2 MR along the line of the proximal trigeminal nerve shows the preganglionic segment between the REZ in the lateral pons and the trigeminal ganglion in the anteroinferior Meckel cave. The CSF within the Meckel cave communicates with the prepontine cistern through the porus trigeminus.*
![First of 5 axial T1 unenhanced MR images extending from the skull base to the mandibular body from superior to inferior is shown. Notice the left maxillary nerve in the foramen rotundum and how it traverses the roof of the pterygopalatine fossa. It then inclines laterally on the back of maxilla and enters the orbit through the inferior orbital fissure, after which it continues as the infraorbital nerve in the floor of the orbit that, in turn, exits the orbit through the infraorbital foramen (not shown).](d85e11be-06d1-43b3-aa8c-6d4abedbe976)
*First of 5 axial T1 unenhanced MR images extending from the skull base to the mandibular body from superior to inferior is shown. Notice the left maxillary nerve in the foramen rotundum and how it traverses the roof of the pterygopalatine fossa. It then inclines laterally on the back of maxilla and enters the orbit through the inferior orbital fissure, after which it continues as the infraorbital nerve in the floor of the orbit that, in turn, exits the orbit through the infraorbital foramen (not shown).*
![Image through the foramen ovale of the skull base is shown. Notice the mandibular nerves exiting the skull base. The vidian canal and nerve are also visible connecting the foramen lacerum to the pterygopalatine fossa. The many black dots within the pterygopalatine fossa are from the normal terminal internal maxillary artery lying anterior to the neural plane.](94d7d00e-afd6-4c0d-b97f-a6b48242dd67)
*Image through the foramen ovale of the skull base is shown. Notice the mandibular nerves exiting the skull base. The vidian canal and nerve are also visible connecting the foramen lacerum to the pterygopalatine fossa. The many black dots within the pterygopalatine fossa are from the normal terminal internal maxillary artery lying anterior to the neural plane.*
### Axial T1 MR
![Image just under the skull base shows mandibular nerves entering the medial upper masticator space. OG lies just below the skull base between CNV3 and tensor veli palatini muscle. Main trunk of CNV3 gives off a meningeal branch and nerve to medial pterygoid with motor root to OG and soon divides into a small anterior division (giving off masseteric, 2 deep temporal nerves to lateral pterygoid motor branches, and a buccal nerve sensory branch) and a large posterior division. Auriculotemporal nerve arises from 2 roots of the proximal posterior division, runs backward encircling the middle meningeal artery, and forms single trunk. The posterior division then divides into terminal branches, inferior alveolar (posterior) and lingual (anterior) nerves.](df754dcd-4113-46db-9c17-41e299c0903b)
*Image just under the skull base shows mandibular nerves entering the medial upper masticator space. OG lies just below the skull base between CNV3 and tensor veli palatini muscle. Main trunk of CNV3 gives off a meningeal branch and nerve to medial pterygoid with motor root to OG and soon divides into a small anterior division (giving off masseteric, 2 deep temporal nerves to lateral pterygoid motor branches, and a buccal nerve sensory branch) and a large posterior division. Auriculotemporal nerve arises from 2 roots of the proximal posterior division, runs backward encircling the middle meningeal artery, and forms single trunk. The posterior division then divides into terminal branches, inferior alveolar (posterior) and lingual (anterior) nerves.*
![MR at the mandibular foramina level shows inferior alveolar nerve runs downward lateral to medial pterygoid and enters mandibular foramen, giving off mylohyoid nerve just before entering mandible.](f2ef1574-bfa2-4e28-8f37-b2f21f5b1917)
*MR at the mandibular foramina level shows inferior alveolar nerve runs downward lateral to medial pterygoid and enters mandibular foramen, giving off mylohyoid nerve just before entering mandible.*
![MR at mandible body level shows inferior alveolar nerve as it exits the mandible via the mental foramen. Lingual nerve contacts the mandible medial to 3rd molar tooth and finally enters the lateral sublingual space compartment.](ea994d2f-37cd-42cc-b8cb-a006b9486103)
*MR at mandible body level shows inferior alveolar nerve as it exits the mandible via the mental foramen. Lingual nerve contacts the mandible medial to 3rd molar tooth and finally enters the lateral sublingual space compartment.*
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---
title: "CNVI (Abducens Nerve)"
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---
## TERMINOLOGY
- ### Abbreviations
- Abducens nerve (CNVI)
- ### Synonyms
- 6th cranial nerve
- CN6
- ### Definitions
- Motor nerve to lateral rectus muscle only
## IMAGING ANATOMY
- ### Overview
- Pure motor nerve with pontine nucleus and 5 anatomic segments
- ### Abducens Nucleus
- Paired CNVI nuclei located in pontine tegmentum (dorsal pons) near midline, just ventral to 4th ventricle
- **Facial colliculus**: Axons of facial nerve (CNVII) loop around abducens nucleus, creating bulge in floor of 4th ventricle
- Isolated lesion to facial colliculus can cause ipsilateral CNVI and CNVII palsy
- ### Intraaxial Segment
- Ipsilateral axons from CNVI nucleus course anteroinferiorly through pontine tegmentum
- ### Cisternal Segment
- Emerges from anterior brainstem near midline through groove between pons and pyramid of medulla oblongata (pontomedullary sulcus)
- Usually exits as single trunk but occasionally duplicated
- Ascends anterosuperiorly in prepontine cistern toward site where it penetrates dura along upper clivus laterally
- Posterior to anterior inferior cerebellar artery in 85%; anterior in 15%
- ### Interdural Segment
- Extends from point where CNVI pierces inner layer dura posteriorly to its entrance into cavernous sinus (CS) anteriorly
- Thin sleeve of arachnoid (and occasionally dura) travels with nerve through this segment
- After penetrating dura, CNVI passes superiorly through basilar venous plexus
- Basilar venous plexus: Interdural; dorsal to upper clivus and located between inner and outer (endosteal) layers of dura
- Nerve remains interdural and passes superiorly over junction of petrous apex and clivus into adjacent venous region, which is referred to as**sphenopetroclival venous confluence** [or simply petroclival confluence or **petroclival venous confluence** (PCVC)]
- PCVC located at junction of posterior part of CS, lateral part of basilar plexus, and anterior part of superior and inferior petrosal sinuses
- In this location, PCVC and interdural segment of CNVI considered to be within **classic Dorello canal**
- Classic **Dorello canal**: Zone/space bounded by petrous apex (inferolaterally), clivus (inferomedially), and **petrosphenoidal ligament of Gruber** (superiorly)
- Proposed modifications expanding limits to include portions of venous confluence above Gruber ligament and making posterior petroclinoid fold as superior boundary
- ### Cavernous Segment
- After exiting Dorello canal, CNVI enters CS and passes laterally around proximal aspect of cavernous internal carotid artery (ICA)
- CNVI: **O****nly cranial nerve to lie within CS**, passing lateral to cavernous ICA
- Cranial nerves III, IV, V1, and V2: All embedded within lateral wall of CS
- ### Extracranial (Intraorbital) Segment
- CNVI enters orbit through **superior orbital fissure (SOF)** together with CNIII and CNIV
- Passes through annulus of Zinn
- Supplies **motor innervation** to **lateral rectus muscle**
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- MR for intraaxial, cisternal, interdural, and cavernous segments
- Thin-section high-resolution T2 and contrast-enhanced T1 in axial and coronal planes
- Depicts small structures, including cranial nerves, surrounded by CSF with high contrast and high spatial resolution
- Bone CT best for skull base and its bony foramina
- ### Imaging Sweet Spots
- Axial and coronal MR sequences should include brainstem, 4th ventricle, CS, and orbit
- CNVI nucleus and intraaxial segment not directly visualized
- CNVI location inferred by identifying facial colliculus in 4th ventricle floor on high-resolution thin-section T2 MR
- Cisternal segment routinely visualized on high-resolution T2 MR
- CNVI entrance into Dorello canal may be visualized due to evagination of CSF into proximal canal
- **CSF sleeve in Dorello canal > 2x width of CNVI**, highly associated with idiopathic intracranial hypertension (**IIH/pseudotumor cerebri**)
- Enhancement of basilar plexus may demonstrate CNVI as tiny, linear, nonenhancing structures
- ### Imaging Pitfalls
- Use of fat saturation on postcontrast T1 MR sequences can amplify blooming (susceptibility) artifact around well-aerated sphenoid sinus
- CS and orbital apex subtle lesions may be obscured by this artifact
- Remove fat saturation and repeat T1 postcontrast MR if this artifact obscures key areas of interest
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- In abducens neuropathy, affected eye will not **abduct**
- CNVI neuropathy divided into **simple** if isolated and **complex** if associated with other cranial nerve involvement
- Simple **CNVI neuropathy most common ocular motor nerve palsy**
- Usually presents as complex cranial neuropathy
- Pontine lesions affect CNVI with CNVII
- CS, SOF lesions affect CNVI with CNIII, CNIV, and CNV1
44c81e26-d954-455a-a408-022ad3f510cc
## Images
### Graphics
![Axial graphic shows the entire length of the abducens nerve from its pontine tegmentum nuclear origin to its motor endplate in the lateral rectus muscle. Follow its progress from the nucleus to its exit at the anteromedial bulbopontine sulcus. From there, note the dural penetration into the Dorello canal leading to its intracavernous portion. Finally, it passes through the superior orbital fissure and the ring of Zinn into the orbit.](images/app.statdx.com_image_thumbnail_48e91253-b086-4f4c-9ee7-8ab878e85533_annotated_false_size_900_quality_90_cf18782cd1af1fa782f8b2e1a5a887a3de0788de.jpg)
*Axial graphic shows the entire length of the abducens nerve from its pontine tegmentum nuclear origin to its motor endplate in the lateral rectus muscle. Follow its progress from the nucleus to its exit at the anteromedial bulbopontine sulcus. From there, note the dural penetration into the Dorello canal leading to its intracavernous portion. Finally, it passes through the superior orbital fissure and the ring of Zinn into the orbit.*
![Axial graphic shows the entire length of the abducens nerve from its pontine tegmentum nuclear origin to its motor endplate in the lateral rectus muscle. Follow its progress from the nucleus to its exit at the anteromedial bulbopontine sulcus. From there, note the dural penetration into the Dorello canal leading to its intracavernous portion. Finally, it passes through the superior orbital fissure and the ring of Zinn into the orbit.](images/app.statdx.com_image_thumbnail_48e91253-b086-4f4c-9ee7-8ab878e85533_size_174_quality_85_59b9b0ed_20251018T124943Z.jpg)
*Axial graphic shows the entire length of the abducens nerve from its pontine tegmentum nuclear origin to its motor endplate in the lateral rectus muscle. Follow its progress from the nucleus to its exit at the anteromedial bulbopontine sulcus. From there, note the dural penetration into the Dorello canal leading to its intracavernous portion. Finally, it passes through the superior orbital fissure and the ring of Zinn into the orbit.*
![Axial graphic shows the entire length of the abducens nerve from its pontine tegmentum nuclear origin to its motor endplate in the lateral rectus muscle. Follow its progress from the nucleus to its exit at the anteromedial bulbopontine sulcus. From there, note the dural penetration into the Dorello canal leading to its intracavernous portion. Finally, it passes through the superior orbital fissure and the ring of Zinn into the orbit.](images/app.statdx.com_image_thumbnail_48e91253-b086-4f4c-9ee7-8ab878e85533_size_174_quality_85_d934cb4adf5c95424af23ea99542442878253bd8.jpg)
*Axial graphic shows the entire length of the abducens nerve from its pontine tegmentum nuclear origin to its motor endplate in the lateral rectus muscle. Follow its progress from the nucleus to its exit at the anteromedial bulbopontine sulcus. From there, note the dural penetration into the Dorello canal leading to its intracavernous portion. Finally, it passes through the superior orbital fissure and the ring of Zinn into the orbit.*
![Sagittal graphic shows the abducens nerve depicted from its origin in the pontine tegmentum to its motor endplate in the lateral rectus muscle. Notice the intraaxial CNVI fibers descend before exiting the bulbopontine sulcus anteriorly. Prepontine cistern CNVI then ascends to pierce the dura into the Dorello canal. Intracavernous CNVI proceeds anteriorly to pass through the superior orbital fissure and the annulus of Zinn before innervating the lateral rectus muscle in orbit.](images/app.statdx.com_image_thumbnail_5f0989cb-616a-47e5-8430-bff384ce39ac_annotated_false_size_900_quality_90_3ff0bd79f77d3b1257219d41047df14994e128be.jpg)
*Sagittal graphic shows the abducens nerve depicted from its origin in the pontine tegmentum to its motor endplate in the lateral rectus muscle. Notice the intraaxial CNVI fibers descend before exiting the bulbopontine sulcus anteriorly. Prepontine cistern CNVI then ascends to pierce the dura into the Dorello canal. Intracavernous CNVI proceeds anteriorly to pass through the superior orbital fissure and the annulus of Zinn before innervating the lateral rectus muscle in orbit.*
### Axial T2 and T1 C+ MR
![Axial T2 MR near the level of the internal auditory canal shows the appearance of the abducens nerve in the prepontine cistern. On the patient's right, CNVI is just exiting the bulbopontine sulcus, while on the left, it is poised to penetrate the dura. Both nerves are rising in the prepontine cistern.](images/app.statdx.com_image_thumbnail_d01bf20c-a4f8-4f4e-bce4-2353f534cf3a_annotated_false_size_900_quality_90_1d95a9fd4ebd67dd1f13757710c05f8e52211abe.jpg)
*Axial T2 MR near the level of the internal auditory canal shows the appearance of the abducens nerve in the prepontine cistern. On the patient's right, CNVI is just exiting the bulbopontine sulcus, while on the left, it is poised to penetrate the dura. Both nerves are rising in the prepontine cistern.*
![Axial T1 C+ MR demonstrates the interdural segment of the abducens nerve within the Dorello canal surrounded by brightly enhancing basilar venous plexus.](images/app.statdx.com_image_thumbnail_a2189f5f-2041-4946-bec2-50223d8d2cde_annotated_false_size_900_quality_90_8249fe9190d022939d45ad500f0e352a64a6db1c.jpg)
*Axial T1 C+ MR demonstrates the interdural segment of the abducens nerve within the Dorello canal surrounded by brightly enhancing basilar venous plexus.*
![Axial T1 C+ MR just above the internal auditory canal shows the abducens nerves passing through the superior basilar venous plexus to enter the posterior margin of the cavernous sinus. At this point, CNVI is arching over the petrous apex below the petrosphenoidal ligament of Gruber into the upper posterior region of the cavernous sinus.](images/app.statdx.com_image_thumbnail_1c2783e7-c377-4460-a5b5-523d71a7e92e_annotated_false_size_900_quality_90_d7c0e0b2790a6f4af2ea2112270a8c12a8090da4.jpg)
*Axial T1 C+ MR just above the internal auditory canal shows the abducens nerves passing through the superior basilar venous plexus to enter the posterior margin of the cavernous sinus. At this point, CNVI is arching over the petrous apex below the petrosphenoidal ligament of Gruber into the upper posterior region of the cavernous sinus.*
### Sagittal T2 MR
![First of 3 sagittal T2 MR images presented from lateral to medial reveals the abducens nerve traversing the prepontine cistern toward the clivus. In this image, the abducens nerve is visible penetrating the dura to enter the Dorello canal, which lies between the cranial dura and periosteum surrounded by the basilar venous plexus.](images/app.statdx.com_image_thumbnail_eb2d6d63-720f-4bae-bc58-84bc85d0977d_annotated_false_size_900_quality_90_5bcf7e68ba7887d92690124a4cfcda8f35216bd7.jpg)
*First of 3 sagittal T2 MR images presented from lateral to medial reveals the abducens nerve traversing the prepontine cistern toward the clivus. In this image, the abducens nerve is visible penetrating the dura to enter the Dorello canal, which lies between the cranial dura and periosteum surrounded by the basilar venous plexus.*
![Image of the brainstem area shows the abducens nerve coursing anterosuperiorly from its exit point from the brainstem (bulbopontine sulcus) toward its point of dural penetration into the Dorello canal. Notice the approximate location of the CNVI nucleus and the steep course that the intraaxial fibers take to reach the bulbopontine sulcus.](45ec936e-39b4-4827-a042-f47565f3523c)
*Image of the brainstem area shows the abducens nerve coursing anterosuperiorly from its exit point from the brainstem (bulbopontine sulcus) toward its point of dural penetration into the Dorello canal. Notice the approximate location of the CNVI nucleus and the steep course that the intraaxial fibers take to reach the bulbopontine sulcus.*
![Image of the brainstem and prepontine cisterns shows the proximal cisternal CNVI closely associated with the belly of the pons. CNIII (oculomotor nerve) is seen passing between the posterior cerebral artery (PCA) and superior cerebellar artery (SCA). More laterally in the perimesencephalic cistern, CNIV (trochlear nerve) also passes between the PCA and SCA (not shown).](a1331b48-1a38-4a18-b9a3-e012d1599f7c)
*Image of the brainstem and prepontine cisterns shows the proximal cisternal CNVI closely associated with the belly of the pons. CNIII (oculomotor nerve) is seen passing between the posterior cerebral artery (PCA) and superior cerebellar artery (SCA). More laterally in the perimesencephalic cistern, CNIV (trochlear nerve) also passes between the PCA and SCA (not shown).*
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---
title: "CNVIII (Vestibulocochlear Nerve)"
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---
## TERMINOLOGY
- ### Abbreviations
- Vestibulocochlear nerve (CNVIII)
- ### Synonyms
- 8th cranial nerve, CN8
- ### Definitions
- CNVIII: Afferent sensory nerve of hearing & balance
## IMAGING ANATOMY
- ### Overview
- Sensory (special sensory afferent) nerve consisting of 2 parts
- Vestibular part: Balance
- Cochlear part: Hearing
- CNVIII best described from peripheral to central
- ### Cochlear Nerve
- Connects organ of Corti to cochlear nuclei & related nuclei of brainstem
- Arises from bipolar neurons located in **spiral ganglion** within modiolus of cochlea
- Peripheral fibers pass to organ of Corti in cochlear duct (scala media) within cochlea
- Central fibers coalesce & pass as auditory component of CNVIII (cochlear nerve) to brainstem
- Central fibers pass from modiolus through cochlear aperture into internal auditory canal (IAC)
- **Cochlear aperture** defined as bony opening into anteroinferior quadrant of fundus of IAC
- Maximum diameter of cochlear aperture: ~ 2 mm
- **Cochlear nerve** passes from IAC fundus to porus acusticus within **anteroinferior q****uadrant of IAC**
- Near porus acusticus, cochlear nerve joins together with superior & inferior vestibular nerves to form vestibulocochlear nerve (CNVIII)
- CNVIII crosses cerebellopontine angle (CPA) cistern posterior to facial nerve
- CNVIII enters lateral brainstem at pontomedullary junction posterior to facial nerve
- Cochlear nerve fibers bifurcate, ending in dorsal & ventral cochlear nuclei
- **Dorsal & ventral cochlear nuclei**
- Cochlear nuclei found on lateral surface of inferior cerebellar peduncle (**restiform body**)
- ### Vestibular Nerve
- Arises from bipolar neurons located in vestibular (**Scarpa**) ganglion located within vestibular nerve in fundal portion of IAC
- Vestibular ganglion not visible on imaging
- Peripheral fibers pass to sensory epithelium of utricle, saccule, & semicircular canals
- Traverse multiple foramina in **macula cribrosa** in lateral wall of IAC fundus
- Larger superior division supplies ampullary crests in lateral & superior semicircular ducts via **lateral & anterior ampullary nerves**
- Smaller inferior division supplies remainder of saccule & posterior semicircular canal ampullary crest via **saccular & singular nerves**
- Central fibers coalesce to form superior & inferior vestibular nerves that pass medially to brainstem
- Fundus of IAC
- Superior & inferior vestibular nerves are separated by **falciform crest** (transverse crest)
- Superior vestibular nerve separated from facial nerve anteriorly by vertical bony structure called **Bill bar**
- Superior & inferior vestibular nerves pass medially from IAC fundus to porus acusticus within posterosuperior & posteroinferior quadrants of IAC
- Near porus acusticus, superior & inferior vestibular nerves join together with cochlear nerve to form vestibulocochlear nerve (CNVIII)
- Vestibulocochlear nerve crosses CPA cistern posterior to facial nerve
- Enters lateral brainstem at junction pons & medulla posterior to facial nerve
- Vestibular nerve fibers divide into ascending & descending branches, which mainly terminate in vestibular nuclear complex
- **Vestibular nuclear complex**
- 4 nuclei (lateral, superior, medial, & inferior)
- Located beneath lateral recess along floor of 4th ventricle (rhomboid fossa) in lower pons
- Complex connections exist between vestibular nuclei, cerebellum, spinal cord (vestibulospinal tract), & nuclei controlling eye movement through medial longitudinal fasciculus (MLF)
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Sensorineural hearing loss (SNHL)
- **Intracochlear lesion suspected**
- CT & MR imaging complimentary to each other
- Congenital lesions of membranous labyrinth seen as abnormalities of fluid spaces on MR or in bony labyrinth shape on T-bone CT
- T-bone CT better for otosclerosis, Paget disease, labyrinthine ossificans, or if trauma suspected
- Only MR will demonstrate labyrinthitis or intralabyrinthine tumor
- **CNVIII****lesion suspected (CPA-IAC)**
- MR imaging method of choice
- Thin-section high-resolution T2 sequence in axial & coronal planes may be used to screen patients with unilateral SNHL
- T1 C+ MR remains gold standard
- ### Imaging Sweet Spots
- Unilateral SNHL
- Focus on brainstem (inferior cerebellar peduncle)-CPA-IAC-cochlea
- Central acoustic pathway (intraaxial pathways above cochlear nuclei) rarely site of offending lesion
- Cisternal & IAC segments of CNVIII routinely visualized on high-resolution T2 MR
- ### Imaging Pitfalls
- Beware small lesions of IAC (≤ 2 mm)
- Follow-up imaging recommended, as may be transient finding where surgery not needed
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Vestibular nerve dysfunction (dizziness, vertigo, imbalance) alone usually has negative MR
- 95% of lesions causing unilateral SNHL found by MR**vestibulocochlear schwannoma**
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## Images
### Graphics
![Axial graphic of the cerebellopontine angle (CPA), internal auditory canal (IAC), &amp; inner ear is shown. Cochlear component of CNVIII begins in bipolar cell bodies in spiral ganglion of cochlear modiolus. Central fibers run in the cochlear nerve to dorsal &amp; ventral cochlear nuclei in the inferior cerebellar peduncle. The inferior &amp; superior vestibular nerves begin in cell bodies in the vestibular ganglion &amp;, from there, course centrally to 4 vestibular nuclei.](images/app.statdx.com_image_thumbnail_dd6d38e6-2cf7-4a62-a73c-26dd75ccdd2b_annotated_false_size_900_quality_90_7beb1c2fd1b29948f1bec0a2546833bb1ef7b1d3.jpg)
*Axial graphic of the cerebellopontine angle (CPA), internal auditory canal (IAC), &amp; inner ear is shown. Cochlear component of CNVIII begins in bipolar cell bodies in spiral ganglion of cochlear modiolus. Central fibers run in the cochlear nerve to dorsal &amp; ventral cochlear nuclei in the inferior cerebellar peduncle. The inferior &amp; superior vestibular nerves begin in cell bodies in the vestibular ganglion &amp;, from there, course centrally to 4 vestibular nuclei.*
![Axial graphic of the cerebellopontine angle (CPA), internal auditory canal (IAC), &amp; inner ear is shown. Cochlear component of CNVIII begins in bipolar cell bodies in spiral ganglion of cochlear modiolus. Central fibers run in the cochlear nerve to dorsal &amp; ventral cochlear nuclei in the inferior cerebellar peduncle. The inferior &amp; superior vestibular nerves begin in cell bodies in the vestibular ganglion &amp;, from there, course centrally to 4 vestibular nuclei.](images/app.statdx.com_image_thumbnail_dd6d38e6-2cf7-4a62-a73c-26dd75ccdd2b_size_174_quality_85_174da57da1b5873f785d9d512153ef8f9977e1a8.jpg)
*Axial graphic of the cerebellopontine angle (CPA), internal auditory canal (IAC), &amp; inner ear is shown. Cochlear component of CNVIII begins in bipolar cell bodies in spiral ganglion of cochlear modiolus. Central fibers run in the cochlear nerve to dorsal &amp; ventral cochlear nuclei in the inferior cerebellar peduncle. The inferior &amp; superior vestibular nerves begin in cell bodies in the vestibular ganglion &amp;, from there, course centrally to 4 vestibular nuclei.*
![Axial graphic of the magnified cochlea, modiolus, &amp; cochlear nerve is shown. Notice the bipolar spiral ganglion cells within modiolus contribute distal fibers to the organ of Corti as well as proximal axons that constitute the cochlear nerve.](images/app.statdx.com_image_thumbnail_d784ce36-3edc-4269-955b-a53ca731713f_annotated_false_size_900_quality_90_41f663c3627626e465097163a65489432c0f46d2.jpg)
*Axial graphic of the magnified cochlea, modiolus, &amp; cochlear nerve is shown. Notice the bipolar spiral ganglion cells within modiolus contribute distal fibers to the organ of Corti as well as proximal axons that constitute the cochlear nerve.*
![Graphic depicting the fundus of the IAC is shown. Notice the crista falciformis separates the cochlear nerve &amp; inferior vestibular nerve below from CNVII &amp; superior vestibular nerve above. Also note the Bill bar separating CNVII from the superior vestibular nerve.](images/app.statdx.com_image_thumbnail_f7afbca5-cced-46b3-a0f6-f9c037db7816_annotated_false_size_900_quality_90_a164cbd202bc312627c8e39e1b56890d2348cc36.jpg)
*Graphic depicting the fundus of the IAC is shown. Notice the crista falciformis separates the cochlear nerve &amp; inferior vestibular nerve below from CNVII &amp; superior vestibular nerve above. Also note the Bill bar separating CNVII from the superior vestibular nerve.*
### Axial Bone CT
![First of 3 axial high-resolution NECT bone window images of the right temporal bone shows the lateral ampullary nerve, which is a branch of the superior vestibular nerve &amp; supplies the ampullary crest in the lateral semicircular canal. The other branch is the anterior ampullary nerve (not shown), which supplies the anterior (superior) semicircular canal ampullary crest.](images/app.statdx.com_image_thumbnail_ab3cc435-70fb-4b42-a229-a2970c4ec34a_annotated_false_size_900_quality_90_af266c0642859c381c643731e54ef460858261c9.jpg)
*First of 3 axial high-resolution NECT bone window images of the right temporal bone shows the lateral ampullary nerve, which is a branch of the superior vestibular nerve &amp; supplies the ampullary crest in the lateral semicircular canal. The other branch is the anterior ampullary nerve (not shown), which supplies the anterior (superior) semicircular canal ampullary crest.*
![This image shows a singulare nerve, which is a branch of the inferior vestibular nerve &amp; supplies the posterior ampullary crest. Also note modiolus in the cochlea, which contains spiral ganglia. The peripheral fibers of the spiral ganglia connect to the organ of Corti, &amp; the central fibers pass through the cochlear aperture &amp; coalesce to form the cochlear nerve, which connects to the brainstem dorsal &amp; ventral cochlear nuclei.](images/app.statdx.com_image_thumbnail_caa23e89-3bff-4812-878e-e03a9791194b_annotated_false_size_900_quality_90_eb7cbb6e60275f407a382854d358609596b0dc77.jpg)
*This image shows a singulare nerve, which is a branch of the inferior vestibular nerve &amp; supplies the posterior ampullary crest. Also note modiolus in the cochlea, which contains spiral ganglia. The peripheral fibers of the spiral ganglia connect to the organ of Corti, &amp; the central fibers pass through the cochlear aperture &amp; coalesce to form the cochlear nerve, which connects to the brainstem dorsal &amp; ventral cochlear nuclei.*
![This image shows another branch of the inferior vestibular nerve, the saccular nerve, which supplies the saccule. Also note the singular canal with a singular nerve &amp; the cochlear aperture.](images/app.statdx.com_image_thumbnail_8c7ee814-74d9-4177-ae1b-7ca1ec31835d_annotated_false_size_900_quality_90_cb489c6f5e002630ad96469d1c176b3d6b7c1687.jpg)
*This image shows another branch of the inferior vestibular nerve, the saccular nerve, which supplies the saccule. Also note the singular canal with a singular nerve &amp; the cochlear aperture.*
### Axial T2 MR
![First of 3 T2 SPACE 3D axial images through the superior aspect of the right IAC shows the facial nerve located anteriorly &amp; the superior vestibular nerve located posteriorly.](9f42ae54-b024-42b5-b19a-2d9d3d52f0c3)
*First of 3 T2 SPACE 3D axial images through the superior aspect of the right IAC shows the facial nerve located anteriorly &amp; the superior vestibular nerve located posteriorly.*
![This image through the inferior aspect of the IAC shows the anteriorly located cochlear nerve exiting through the cochlear aperture. The modiolus appears dark on the T2-weighted image, which contains the spiral ganglion. Posteriorly, the inferior vestibular nerve &amp; a loop of the anteroinferior cerebellar artery in the medial aspect of the canal are also depicted.](7fe98219-8222-424f-8ed2-9e3ccb4b2556)
*This image through the inferior aspect of the IAC shows the anteriorly located cochlear nerve exiting through the cochlear aperture. The modiolus appears dark on the T2-weighted image, which contains the spiral ganglion. Posteriorly, the inferior vestibular nerve &amp; a loop of the anteroinferior cerebellar artery in the medial aspect of the canal are also depicted.*
![This image shows the CPA cisternal segment of facial nerve anteriorly &amp; CPA cisternal segment of vestibulocochlear nerve posteriorly; they enter the brainstem at the lateral pontomedullary junction.](e750cd78-2bf0-4158-86c8-7c81ca5194c9)
*This image shows the CPA cisternal segment of facial nerve anteriorly &amp; CPA cisternal segment of vestibulocochlear nerve posteriorly; they enter the brainstem at the lateral pontomedullary junction.*
### Coronal T2 MR
![First of 3 coronal T2 SPACE MR reformatted images of the right temporal bone through the anterior aspect of the IAC shows the superior facial nerve and the inferior cochlear nerve in the fundus region. Note a small bone projection, the crista falciformis, which separates the IAC into the superior and inferior halves at the fundus. These are further divided into 4 quadrants by a vertically oriented Bill bar.](dedf5fcc-c791-4bb5-bc2c-86dd01debc35)
*First of 3 coronal T2 SPACE MR reformatted images of the right temporal bone through the anterior aspect of the IAC shows the superior facial nerve and the inferior cochlear nerve in the fundus region. Note a small bone projection, the crista falciformis, which separates the IAC into the superior and inferior halves at the fundus. These are further divided into 4 quadrants by a vertically oriented Bill bar.*
![This image through the middle of the IAC shows all 4 nerves, including the superior &amp; inferior vestibular nerves &amp; facial &amp; cochlear nerves.](bf67e607-653c-4230-a5d1-10942cf725d8)
*This image through the middle of the IAC shows all 4 nerves, including the superior &amp; inferior vestibular nerves &amp; facial &amp; cochlear nerves.*
![This image through the posterior aspect of the canal shows convergence of the cochlear, superior, &amp; inferior vestibular nerves, which form a common trunk of the vestibulocochlear nerve at the porus acusticus. The facial nerve is seen anterior &amp; superior to the vestibulocochlear nerve at the porus acusticus.](9511bb02-93af-4fde-a603-2756e90aecfa)
*This image through the posterior aspect of the canal shows convergence of the cochlear, superior, &amp; inferior vestibular nerves, which form a common trunk of the vestibulocochlear nerve at the porus acusticus. The facial nerve is seen anterior &amp; superior to the vestibulocochlear nerve at the porus acusticus.*
### Oblique Sagittal T2 MR
![First of 3 sagittal oblique T2 SPACE 3D reformatted images of the temporal bone through the fundus of the IAC shows all 4 nerves, including anterosuperiorly located facial nerve, anteroinferiorly located cochlear nerve, posterosuperiorly located superior vestibular nerve, &amp; posteroinferiorly located inferior vestibular nerve. Note that the crista falciformis divides the canal into superior and inferior halves. The anterior and posterior division is by the Bill bar (not seen on imaging).](e66ad0bf-feb6-4ae5-96b8-32b1918a61f6)
*First of 3 sagittal oblique T2 SPACE 3D reformatted images of the temporal bone through the fundus of the IAC shows all 4 nerves, including anterosuperiorly located facial nerve, anteroinferiorly located cochlear nerve, posterosuperiorly located superior vestibular nerve, &amp; posteroinferiorly located inferior vestibular nerve. Note that the crista falciformis divides the canal into superior and inferior halves. The anterior and posterior division is by the Bill bar (not seen on imaging).*
![This image through the mid-IAC shows the convergence of the cochlear, superior, &amp; inferior vestibular nerves forming the appearance of a catcher's mitt with the facial nerve as the ball in it.](5c095339-dbee-421d-8872-e9fffb7f6085)
*This image through the mid-IAC shows the convergence of the cochlear, superior, &amp; inferior vestibular nerves forming the appearance of a catcher's mitt with the facial nerve as the ball in it.*
![This image at the porus acusticus shows the vestibulocochlear nerve posterior and inferior to the facial nerve.](84fe660c-e4c6-4fc3-83b2-1883ef5e9211)
*This image at the porus acusticus shows the vestibulocochlear nerve posterior and inferior to the facial nerve.*
### Additional Images
![Axial bone CT through the upper portion of the IAC shows the C-shaped labyrinthine segment of the facial nerve &amp; a main canal of the superior vestibular nerve crossing the cribriform plate toward the vestibule.](ab657603-f699-4539-968e-184fd81c2730)
*Axial bone CT through the upper portion of the IAC shows the C-shaped labyrinthine segment of the facial nerve &amp; a main canal of the superior vestibular nerve crossing the cribriform plate toward the vestibule.*
![Axial bone CT through the lower IAC shows anterolateral cochlear aperture through which the cochlear nerve passes on its way from the cochlear modiolus into the IAC. Also notice the cribriform plate foramen through which the inferior vestibular nerve reaches the vestibule &amp; the smaller singular canal.](4fea98a5-8432-42c8-9d22-bc6a20c0b10d)
*Axial bone CT through the lower IAC shows anterolateral cochlear aperture through which the cochlear nerve passes on its way from the cochlear modiolus into the IAC. Also notice the cribriform plate foramen through which the inferior vestibular nerve reaches the vestibule &amp; the smaller singular canal.*
![Coronal bone CT through the IAC demonstrates the horizontal falciform crest, which divides the fundus of the IAC into upper &amp; lower portions. The facial &amp; superior vestibular nerves pass above &amp; cochlear &amp; inferior vestibular nerves pass below the falciform crest. Porus acusticus is a bony aperture of the IAC.](cc855e64-9e38-43b8-bab0-a455e131d264)
*Coronal bone CT through the IAC demonstrates the horizontal falciform crest, which divides the fundus of the IAC into upper &amp; lower portions. The facial &amp; superior vestibular nerves pass above &amp; cochlear &amp; inferior vestibular nerves pass below the falciform crest. Porus acusticus is a bony aperture of the IAC.*
![First of 3 axial T2 MR images presented from inferior to superior through the CPA cistern &amp; IAC is shown. The section through the superior left IAC demonstrates the cochlear nerve anteriorly &amp; inferior vestibular nerve posteriorly at the fundus.](8b50ef1f-4996-4bc7-aa2f-8cc8d6a0fb1c)
*First of 3 axial T2 MR images presented from inferior to superior through the CPA cistern &amp; IAC is shown. The section through the superior left IAC demonstrates the cochlear nerve anteriorly &amp; inferior vestibular nerve posteriorly at the fundus.*
![Vestibulocochlear nerve arises posterior to the facial nerve from the brainstem at the pontomedullary junction &amp; maintains a posterior position throughout its course through the CPA/IAC. On the patient's right, the cochlear nerve is anterior to inferior vestibular nerve within the fundus of the IAC. On the left, the superior fundus of the IAC is seen with the anterior facial nerve &amp; posterior superior vestibular nerve.](63129ff7-1d7a-400a-a70c-591aec9ab635)
*Vestibulocochlear nerve arises posterior to the facial nerve from the brainstem at the pontomedullary junction &amp; maintains a posterior position throughout its course through the CPA/IAC. On the patient's right, the cochlear nerve is anterior to inferior vestibular nerve within the fundus of the IAC. On the left, the superior fundus of the IAC is seen with the anterior facial nerve &amp; posterior superior vestibular nerve.*
![MR slice through the superior IAC area demonstrates the superior vestibular nerve posterior to facial nerve on the patient's right.](cc775721-993e-446e-9d73-107b2d1e4302)
*MR slice through the superior IAC area demonstrates the superior vestibular nerve posterior to facial nerve on the patient's right.*
![First of 3 coronal T2 MR images presented from posterior to anterior is shown. Vestibulocochlear nerve emerges from the brainstem posterior to the facial nerve at the pontomedullary junction.](c37e7997-96a5-4d30-86f6-764b48b008b2)
*First of 3 coronal T2 MR images presented from posterior to anterior is shown. Vestibulocochlear nerve emerges from the brainstem posterior to the facial nerve at the pontomedullary junction.*
![Facial &amp; vestibulocochlear nerves course through the CPA into the IAC. Facial nerve is anterior &amp; superior to the vestibulocochlear nerve within the CPA &amp; IAC. Notice the somewhat cephalad course of CNVIII as it rises into the IAC from its origin at the pontomedullary junction.](8753d5fd-f96e-42b4-8ba9-64f174b2fae8)
*Facial &amp; vestibulocochlear nerves course through the CPA into the IAC. Facial nerve is anterior &amp; superior to the vestibulocochlear nerve within the CPA &amp; IAC. Notice the somewhat cephalad course of CNVIII as it rises into the IAC from its origin at the pontomedullary junction.*
![Section through the fundus of the IAC demonstrates the horizontal falciform crest separating the fundus into upper &amp; lower portions. At this level, the facial nerve is above &amp; the cochlear nerve is below the falciform crest. The anteroinferior cerebellar artery loop is a constant fixture in the normal anatomy of the CPA &amp; IAC area.](6c181e2c-11aa-48e1-ae7a-5177d30b9d56)
*Section through the fundus of the IAC demonstrates the horizontal falciform crest separating the fundus into upper &amp; lower portions. At this level, the facial nerve is above &amp; the cochlear nerve is below the falciform crest. The anteroinferior cerebellar artery loop is a constant fixture in the normal anatomy of the CPA &amp; IAC area.*
![First of 3 sequential oblique sagittal T2 MR images through the IAC presented from lateral to medial is shown. This slice through the fundus of the IAC shows the horizontal falciform crest separating the fundus into upper &amp; lower portions. The facial nerve is anterosuperior, separated from the superior vestibular nerve by a vertical bony septum called the Bill bar, which is not resolved with even focused imaging. Below the falciform crest are the cochlear nerve anteriorly &amp; inferior vestibular nerve posteriorly.](063cca59-efa4-4650-8e87-a4c1878468c3)
*First of 3 sequential oblique sagittal T2 MR images through the IAC presented from lateral to medial is shown. This slice through the fundus of the IAC shows the horizontal falciform crest separating the fundus into upper &amp; lower portions. The facial nerve is anterosuperior, separated from the superior vestibular nerve by a vertical bony septum called the Bill bar, which is not resolved with even focused imaging. Below the falciform crest are the cochlear nerve anteriorly &amp; inferior vestibular nerve posteriorly.*
![In the mid IAC, this image shows 4 discrete nerves.](84f3fbd0-5820-4098-8cc2-3b3c280c70e8)
*In the mid IAC, this image shows 4 discrete nerves.*
![At the level of the porus acusticus, both the superior &amp; inferior vestibular nerves join together with the cochlear nerve to form a C-shaped vestibulocochlear nerve. The facial nerve remains discrete as it travels across the CPA cistern.](13be2f02-4ba1-4653-89fb-022c3ec7e88a)
*At the level of the porus acusticus, both the superior &amp; inferior vestibular nerves join together with the cochlear nerve to form a C-shaped vestibulocochlear nerve. The facial nerve remains discrete as it travels across the CPA cistern.*
docs_md/articles/cnx-vagus-nerve_83868689-c995-4608-bed3-f59664cbd586.md
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---
title: "CNX (Vagus Nerve)"
docid: "83868689-c995-4608-bed3-f59664cbd586"
authors:
- key: "30274529-c61b-4267-94db-736fecd85af3"
value: "Aparna Singhal, MD"
- key: "33151213-01b2-4542-9105-342e006b3915"
value: "H. Ric Harnsberger, MD"
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name: "Head and Neck"
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name: "Anatomy"
slug: "anatomy"
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name: "Cranial Nerves"
slug: "cranial-nerves"
treeNodeId: "bc7da3a0-2ad7-4f30-949a-0db0d1e6f620"
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name: "CNX (Vagus Nerve)"
slug: "cnx-vagus-nerve"
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category: "Head and Neck"
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lastUpdated: "02/01/24"
pageDescription: "CNX (Vagus Nerve)"
pageKeywords: "Head and Neck, Anatomy, Cranial Nerves, CNX (Vagus Nerve)"
pageTitle: "CNX (Vagus Nerve) | STATdx"
enhancedTitle: "CNX (Vagus Nerve)"
type: "ANATOMY"
breadcrumbs:
- "Head and Neck"
- "Anatomy"
- "Cranial Nerves"
- "CNX (Vagus Nerve)"
---
## TERMINOLOGY
- ### Abbreviations
- Vagus nerve (CNX)
- ### Synonyms
- CN10
- ### Definitions
- CNX: Longest & one of most complex cranial nerves (CNs) with complex functions, including parasympathetic (PS) innervation of neck, thoracic & abdominal viscera
- Involved in autonomic regulation of cardiovascular, respiratory, & gastrointestinal systems
- Additional innervation
- Motor to majority of soft palate, pharynx, larynx, & palatoglossus tongue muscle
- Visceral sensation from larynx, esophagus, trachea, thoracic & abdominal viscera
- Sensory nerve to external tympanic membrane (TM), external auditory canal (EAC), & external ear
- Taste from epiglottis
## IMAGING ANATOMY
- ### Overview
- Longest of CNs, extending from medulla to colon
- Segments: Intraaxial, cisternal, skull base, & extracranial
- ### Intraaxial Segment
- Vagal nuclei in upper & middle medulla
- **Motor fibers** originate in **nucleus ambiguus**
- **Taste** from epiglottis goes to **solitary tract nucleus**
- **Sensory fibers** from viscera go to **dorsal motor vagal nucleus** (afferent component)
- **PS or visceral motor fibers** project from **dorsal motor vagal nucleus**(efferent component)
- Sensations from meninges, laryngeal mucosa, & ear to spinal nucleus CNV
- ### Cisternal Segment
- Nerve fibers exit lateral medulla in **postolivary sulcus** inferior to CNIX & superior to bulbar portion of CNXI
- ### Skull Base Segment
- Enters **pars vascularis** portion of jugular foramen (JF)
- With CNXI (shared fibrous sheath) & jugular bulb
- **Superior vagal (jugular) ganglion** found within JF
- ### Extracranial Segment
- Exits JF into nasopharyngeal **carotid space**
- **Inferior vagal (nodose) ganglion** lies just below skull base
- Travels posterolateral to carotid artery into thorax
- Goes anterior to aortic arch on left & subclavian artery (SCA) on right
- Forms plexus around esophagus & major blood vessels to heart & lungs
- Esophageal plexus nerves provide PS supply to stomach
- Innervation to intestines & visceral organs follows arterial blood supply
- ### Extracranial Branches in Head & Neck
- **Auricular branch (Arnold nerve)**
- Sensation from external surface of TM, EAC, & external ear
- From superior vagal ganglion within JF (also has CNIX branches), passes through **mastoid canaliculus** from posterolateral JF to mastoid segment CNVII canal, enters EAC via tympanomastoid fissure
- **Pharyngeal branches**
- **Pharyngeal plexus** exits just below skull base
- Sensory to epiglottis, trachea, & esophagus
- Motor to soft palate [except tensor veli palatini muscle (CNV3)] & pharyngeal constrictor muscles
- **Superior laryngeal nerve**
- Motor to **cricothyroid** muscle (external branch)
- Sensory internal branch to hypopharynx & supraglottis
- **Recurrent laryngeal nerve (RLN)**
- On right, recurs at cervicothoracic junction, passes posteriorly around SCA
- On left, recurs in mediastinum, passes posteriorly under aorta at aortopulmonary window (APW)
- Travels in **tracheoesophageal groove** (TEG) posteromedial to thyroid lobe & enters larynx at cricothyroid joint level
- Motor to all laryngeal muscles except cricothyroids
- Sensory to mucosa of infraglottis
- **Carotid sinus branch (Hering nerve)**
- Formed by small CNIX branch & branch from CNX
- Supplies carotid sinus wall baroreceptors & carotid body chemoreceptors
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- **Proximal vagal neuropathy**
- Image from medulla to hyoid bone
- MR imaging method of choice: Superior sensitivity for skull base, meningeal, cisternal, & brainstem pathology
- Must have axial, coronal T2, T1 (without fat saturation & contrast-enhanced with fat saturation), heavily T2-weighted steady state (e.g., FIESTA/CISS) sequence
- May be indistinguishable sometimes from CNXI & IX
- Bone CT complementary in skull base pathology
- **Distal vagal neuropathy**
- Image skull base to mediastinum; **to carina for left side**
- Key areas to evaluate: Carotid space, TEG, APW
- CECT imaging method of choice
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- **Vagal nerve dysfunction:****Proximal symptom complex**
- Injury site: Between medulla & hyoid bone
- Multiple CNs involved (CNIX-XII, Vernet syndrome) with oropharyngeal & laryngeal dysfunction, including deviation of uvula to opposite side & ipsilateral loss of pharyngeal reflex & vocal cord (VC) paralysis
- **Vagal nerve dysfunction:****Distal symptom complex**
- Injury site: Below hyoid bone
- Isolated larynx dysfunction with VC paralysis (RLN involvement > > infrahyoid CNX)
- Imaging features of VC paralysis: Medialization of ipsilateral true VC, anteromedial arytenoid cartilage rotation, enlarged laryngeal ventricle = sail sign, medialized, thickened aryepiglottic fold, enlarged pyriform sinus
- Injury to vagus branches-RLN (on left, from aortic arch pathology, surgery, during inferior thyroid artery ligation, etc.), internal branch of SLN (from trauma or lymphadenopathy), & external branch of SLN (from superior thyroid artery ligation)
- **Non-RLN**: Rare, enters larynx without thoracic descent (> common right with aberrant right SCA), can get injured during thyroid/spine surgery
cb92e9e5-c27b-4906-af62-f3f2d0ab386f
## Images
### Graphics, Proximal CNX
![Graphic of the brainstem viewed from behind shows critical nuclear columns of CNX. Note the nucleus ambiguus supplies motor fibers to CNX. The dorsal vagal nucleus is a mixed nucleus, sending efferent parasympathetic fibers to the viscera while receiving afferent sensory fibers from these same viscera. The solitary tract nucleus receives taste information from the epiglottis and vallecula via CNX.](images/app.statdx.com_image_thumbnail_49808556-8ea5-4fdf-8a80-170f28e0213f_annotated_false_size_900_quality_90_d9dd0d060935faa6e3e18cde527eea9afbe64b2d.jpg)
*Graphic of the brainstem viewed from behind shows critical nuclear columns of CNX. Note the nucleus ambiguus supplies motor fibers to CNX. The dorsal vagal nucleus is a mixed nucleus, sending efferent parasympathetic fibers to the viscera while receiving afferent sensory fibers from these same viscera. The solitary tract nucleus receives taste information from the epiglottis and vallecula via CNX.*
![Graphic of the brainstem viewed from behind shows critical nuclear columns of CNX. Note the nucleus ambiguus supplies motor fibers to CNX. The dorsal vagal nucleus is a mixed nucleus, sending efferent parasympathetic fibers to the viscera while receiving afferent sensory fibers from these same viscera. The solitary tract nucleus receives taste information from the epiglottis and vallecula via CNX.](images/app.statdx.com_image_thumbnail_49808556-8ea5-4fdf-8a80-170f28e0213f_size_174_quality_85_2cb3b139978b6cc2df89f39fbafbe6ad3596e098.jpg)
*Graphic of the brainstem viewed from behind shows critical nuclear columns of CNX. Note the nucleus ambiguus supplies motor fibers to CNX. The dorsal vagal nucleus is a mixed nucleus, sending efferent parasympathetic fibers to the viscera while receiving afferent sensory fibers from these same viscera. The solitary tract nucleus receives taste information from the epiglottis and vallecula via CNX.*
![Axial graphic through the medulla shows principal nuclei associated with vagus nerve function. Skeletal motor fibers to the pharynx and larynx come from the nucleus ambiguus. This nucleus also contributes to CNIX and CNXI. Parasympathetic fibers to the viscera are associated with the dorsal motor nucleus of the vagus nerve (solid pink line). Sensory information transmitted from the viscera is also transmitted to the dorsal nucleus of the vagus nerve (dashed pink line). Via the vagus nerve, the solitary tract nucleus receives taste information from the epiglottis and afferent information from the aortic bodies and sinoatrial node, in addition to various visceral afferents via other cranial nerves.](images/app.statdx.com_image_thumbnail_b39531df-04a8-4764-b126-81c547944773_annotated_false_size_900_quality_90_c40db0141881ac920e9738240f3235108c3db71c.jpg)
*Axial graphic through the medulla shows principal nuclei associated with vagus nerve function. Skeletal motor fibers to the pharynx and larynx come from the nucleus ambiguus. This nucleus also contributes to CNIX and CNXI. Parasympathetic fibers to the viscera are associated with the dorsal motor nucleus of the vagus nerve (solid pink line). Sensory information transmitted from the viscera is also transmitted to the dorsal nucleus of the vagus nerve (dashed pink line). Via the vagus nerve, the solitary tract nucleus receives taste information from the epiglottis and afferent information from the aortic bodies and sinoatrial node, in addition to various visceral afferents via other cranial nerves.*
### Graphic, Extracranial Vagus Nerve
![Lateral graphic shows the neck and upper mediastinal portions of CNX, including the 4 brainstem nuclei. The nucleus ambiguus supplies efferent motor innervation (green lines) via the pharyngeal plexus to the soft palate and pharynx (superior, middle, and inferior constrictor muscles) and via the recurrent laryngeal nerves to all laryngeal muscles except the cricothyroids. The dual-functioning dorsal vagal nucleus both sends out efferent fibers for involuntary motor activity in the viscera (solid pink line) and receives sensations from these same viscera (dashed pink line). The solitary tract nucleus receives taste information from the region of the epiglottis and vallecula. The spinal nucleus of CNV receives external ear and skull base-meninges sensory information. Only the visceral motor and sensory fibers from dorsal vagal nucleus continue on CNX to the rest of the body.](images/app.statdx.com_image_thumbnail_3b128bfa-2164-49b7-a4af-6a852303de83_annotated_false_size_900_quality_90_3c45390bec220f98cdd471edcd3d4c3bd831e645.jpg)
*Lateral graphic shows the neck and upper mediastinal portions of CNX, including the 4 brainstem nuclei. The nucleus ambiguus supplies efferent motor innervation (green lines) via the pharyngeal plexus to the soft palate and pharynx (superior, middle, and inferior constrictor muscles) and via the recurrent laryngeal nerves to all laryngeal muscles except the cricothyroids. The dual-functioning dorsal vagal nucleus both sends out efferent fibers for involuntary motor activity in the viscera (solid pink line) and receives sensations from these same viscera (dashed pink line). The solitary tract nucleus receives taste information from the region of the epiglottis and vallecula. The spinal nucleus of CNV receives external ear and skull base-meninges sensory information. Only the visceral motor and sensory fibers from dorsal vagal nucleus continue on CNX to the rest of the body.*
### Graphics, Extracranial CNX
![Axial graphic of the nasopharyngeal carotid spaces shows the extracranial vagus nerve situated posteriorly in the gap between the internal carotid artery and the internal jugular vein. Notice that at this level, CNIX, CNXI, and CNXII are all still within the carotid space.](images/app.statdx.com_image_thumbnail_065237dc-c884-43e6-8235-27c838576b5e_annotated_false_size_900_quality_90_eefbff31277d7684c66a3e4822bcc5b55d8e70dc.jpg)
*Axial graphic of the nasopharyngeal carotid spaces shows the extracranial vagus nerve situated posteriorly in the gap between the internal carotid artery and the internal jugular vein. Notice that at this level, CNIX, CNXI, and CNXII are all still within the carotid space.*
![Axial graphic through the infrahyoid carotid spaces at the level of the thyroid gland demonstrates the vagus trunk is the only remaining cranial nerve within the carotid space. It remains in the posterior gap between the common carotid artery and the internal jugular vein. Note the recurrent laryngeal nerve in the tracheoesophageal groove with the visceral space. Remember the left recurrent laryngeal nerve turns cephalad in the aortopulmonic window in the mediastinum, whereas the right recurrent nerve turns at the cervicothoracic junction around the subclavian artery.](4b264956-7f35-4130-8ccf-11c098acaede)
*Axial graphic through the infrahyoid carotid spaces at the level of the thyroid gland demonstrates the vagus trunk is the only remaining cranial nerve within the carotid space. It remains in the posterior gap between the common carotid artery and the internal jugular vein. Note the recurrent laryngeal nerve in the tracheoesophageal groove with the visceral space. Remember the left recurrent laryngeal nerve turns cephalad in the aortopulmonic window in the mediastinum, whereas the right recurrent nerve turns at the cervicothoracic junction around the subclavian artery.*
### Axial Bone CT
![First of 3 axial bone CT images of the skull base presented from superior to inferior is shown. The jugular foramen is divided by the jugular spine into the anteromedial smaller pars nervosa, and posterolateral pars vascularis. The pars vascularis transmits the vagus and accessory cranial nerves, Arnold nerve, and jugular bulb, which becomes the internal jugular vein.](f8c0ebe5-ca0d-48a2-86bd-5aaa90633434)
*First of 3 axial bone CT images of the skull base presented from superior to inferior is shown. The jugular foramen is divided by the jugular spine into the anteromedial smaller pars nervosa, and posterolateral pars vascularis. The pars vascularis transmits the vagus and accessory cranial nerves, Arnold nerve, and jugular bulb, which becomes the internal jugular vein.*
![In this image, the pars nervosa is seen to connect anteromedially to the inferior petrosal sinus. CNIX, the Jacobsen nerve, and the inferior petrosal sinus are all found within the pars nervosa.](5912a00a-7d4d-4a4f-bd20-37f02f073c09)
*In this image, the pars nervosa is seen to connect anteromedially to the inferior petrosal sinus. CNIX, the Jacobsen nerve, and the inferior petrosal sinus are all found within the pars nervosa.*
![Image through the lower jugular foramen shows the sigmoid sinuses emptying into the pars vascularis of the jugular foramen. Notice the jugular foramen is located on the floor of the posterior cranial fossa in the seam between the petrous temporal bone anterolaterally and occipital bone posteromedially.](ce621e02-3a2a-4a1f-965d-22360a27e021)
*Image through the lower jugular foramen shows the sigmoid sinuses emptying into the pars vascularis of the jugular foramen. Notice the jugular foramen is located on the floor of the posterior cranial fossa in the seam between the petrous temporal bone anterolaterally and occipital bone posteromedially.*
### Axial T2 MR
![First of 3 axial T2 MR images of the low brainstem presented from superior to inferior is shown. The vagus nerve is seen exiting the lateral medulla in the postolivary sulcus inferior to the glossopharyngeal nerve.](ec10be8a-9f11-480c-bf0a-73c9e3f46895)
*First of 3 axial T2 MR images of the low brainstem presented from superior to inferior is shown. The vagus nerve is seen exiting the lateral medulla in the postolivary sulcus inferior to the glossopharyngeal nerve.*
![In this image, the vagus nerve is seen exiting the postolivary sulcus into the lateral basal cistern bilaterally. A portion of the cisternal glossopharyngeal nerve, CNIX, is seen on the left.](31a4d8db-facf-45b4-a398-4b35f93764d5)
*In this image, the vagus nerve is seen exiting the postolivary sulcus into the lateral basal cistern bilaterally. A portion of the cisternal glossopharyngeal nerve, CNIX, is seen on the left.*
![At the level of the lower aspect of the jugular foramen, the cisternal portion of the bulbar portion of the accessory nerve, CNXI, is seen close to the postolivary sulcus. The vagus nerve is seen entering the jugular foramen laterally. Without thin-section focused T2 MR imaging, it is often difficult to separate the glossopharyngeal nerve, vagus nerve, and bulbar root of the accessory nerve in the basal cisterns.](b75d7b1e-cace-4707-b1e2-a0ced0d6afcc)
*At the level of the lower aspect of the jugular foramen, the cisternal portion of the bulbar portion of the accessory nerve, CNXI, is seen close to the postolivary sulcus. The vagus nerve is seen entering the jugular foramen laterally. Without thin-section focused T2 MR imaging, it is often difficult to separate the glossopharyngeal nerve, vagus nerve, and bulbar root of the accessory nerve in the basal cisterns.*
### Pathology examples
![Axial T2 FS MR demonstrates a hyperintense right jugular foramen mass with adjacent osseous remodeling. Note the lack of flow voids, which will be a feature of a paraganglioma, another differential consideration for a jugular foramen mass.](e95e4cdd-26da-4231-92eb-299ca9cf427c)
*Axial T2 FS MR demonstrates a hyperintense right jugular foramen mass with adjacent osseous remodeling. Note the lack of flow voids, which will be a feature of a paraganglioma, another differential consideration for a jugular foramen mass.*
![Coronal CT shows a large right jugular foramen mass with smooth erosion or remodeling of the jugular foramen bony margins. The right lateral jugular tubercle (also called the &quot;bird's beak&quot;) is eroded, whereas the left side is intact. The primary differential for a mass with these features is a schwannoma.](00dc6218-d729-4782-9e89-72ef74acdb18)
*Coronal CT shows a large right jugular foramen mass with smooth erosion or remodeling of the jugular foramen bony margins. The right lateral jugular tubercle (also called the &quot;bird's beak&quot;) is eroded, whereas the left side is intact. The primary differential for a mass with these features is a schwannoma.*
![Coronal T1 C+ FS MR demonstrates a lobulated, heterogeneously enhancing mass arising from the right jugular foramen. Note the typical superomedial vector of spread toward the brainstem; contrast this with a paraganglioma that tends to grow superolaterally toward the middle ear.](c2410556-0b3e-415e-b0d6-c5d2310d0169)
*Coronal T1 C+ FS MR demonstrates a lobulated, heterogeneously enhancing mass arising from the right jugular foramen. Note the typical superomedial vector of spread toward the brainstem; contrast this with a paraganglioma that tends to grow superolaterally toward the middle ear.*
### Vagal nerve nuclei
![Table depicting the vagus nerve nuclei with the structures innervated and some of the interactions of these nuclei with other cranial nerves is shown.](ff008b7f-e7ac-4fb8-9d87-06566cee928b)
*Table depicting the vagus nerve nuclei with the structures innervated and some of the interactions of these nuclei with other cranial nerves is shown.*
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title: "CNXI (Accessory Nerve)"
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---
## TERMINOLOGY
- ### Abbreviations
- Accessory nerve (CNXI)
- ### Synonyms
- 11th cranial nerve (CN), CN11
- ### Definitions
- CNXI: Pure motor CN, supplying sternocleidomastoid (SCM), trapezius muscles (through spinal component) and palatal, pharyngeal, and laryngeal muscles (through cranial component)
## IMAGING ANATOMY
- ### Overview
- Motor CN only
- 4 CNXI segments are defined
- Intraaxial, cisternal, skull base, and extracranial
- ### Intraaxial Segment
- 2 distinct nuclear origins
- **Bulbar** (cranial) motor fibers originate in lower **nucleus ambiguus**
- Fibers course anterolaterally to exit lateral medulla in postolivary sulcus inferior to CNIX and CNX
- **Spinal** motor fibers originate from **spinal nucleus** of accessory nerve
- Narrow column of cells along lateral aspect of anterior horn from C1 to C5
- Nerve fibers emerge from lateral aspect of cervical spinal cord between anterior and posterior roots
- Fibers combine, forming bundle that ascends, entering posterior cranial fossa via**foramen magnum**
- ### Cisternal Segment
- Bulbar portion travels anterolaterally through basal cistern along similar course as CNIX and CNX
- Spinal portion enters lower lateral basal cistern, exits through jugular foramen
- Bulbar root joins spinal component of accessory nerve either in lower cistern or within jugular foramen
- ### Skull Base Segment
- Passes through posterior **pars vascularis portion of jugular foramen**
- CNX and jugular bulb are also in pars vascularis
- Bulbar and spinal portions remain together in jugular foramen
- ### Extracranial Segment
- Fibers from bulbar portion (nucleus ambiguus) separate from main nerve and merge with vagus nerve
- Travel via CNX to supply muscles of
- Palate: Levator veli palatini, palatoglossus, palatopharyngeus, and musculus uvulae
- Pharynx: Superior constrictor and soft palate via pharyngeal plexus
- Larynx: Except cricothyroid muscle via recurrent laryngeal nerve
- Fibers from spinal portion remain in extracranial CNXI
- Diverges posterolaterally from carotid space
- Enters deep surface of upper portion of SCM, anastomoses with C2 &/or C3 fibers, exits posterior border around midportion of SCM
- Continues across floor of posterior cervical space to anterior border of trapezius
- Often forms plexus along with branches from C2 to C4 before entering and terminating in trapezius
- **Innervates SCM and trapezius muscles**
- Rarely terminates in SCM, trapezius being supplied by cervical nerves
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- MR imaging method of choice
- Superior sensitivity to skull base, meningeal, cisternal, and brainstem pathology
- Sequences should include combination of T2, T1 without fat saturation, and contrast-enhanced T1 with fat saturation in axial and coronal planes
- Bone CT used to supplement MR when complex skull base pathology is present
- ### Imaging Sweet Spots
- CNXI nuclei and intraaxial segment not directly visualized
- Cisternal segment is often not visualized on routine MR imaging
- High-resolution thin-section T2 MR sequence usually demonstrates CNIX-XI nerve complex passing through basal cisterns from postolivary sulcus to pars vascularis of jugular foramen
- Bone CT clearly demonstrates bony anatomy of pars vascularis of jugular foramen
- Extracranial CNXI segment not identifiable in conventional imaging
- Location inferred from its constant position deep to SCM muscle in floor of posterior cervical space
- MR neurography techniques, such as 3D CRANI and PSIF, can demonstrate extracranial course
- ### Imaging Pitfalls
- Hypertrophic levator scapulae muscle following serious CNXI injury may mimic tumor
- **Do not mistake this enlarged muscle for mass**
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- CNXI innervates SCM and trapezius muscles
- ### Function & Dysfunction
- CNXI dysfunction: Isolated CNXI injury
- Most common cause is radical neck dissection because jugular nodal chain intimately associated with CNXI
- Initial symptoms of spinal accessory neuropathy
- Downward and lateral rotation of scapula
- Shoulder droop resulting from loss of trapezius tone
- Long-term findings in spinal accessory neuropathy
- Within 6 months results in **atrophy** of ipsilateral SCM and trapezius muscles
- **Compensatory hypertrophy** of ipsilateral **levator scapulae muscle** occurs over months
0146bcf2-ee8b-4439-a4fc-8f94c54fa6f6
## Images
### Graphics
![Graphic of the posterior brainstem reveals both the spinal and the bulbar roots of the accessory nerve (CNXI). Note the lower nucleus ambiguus gives rise to multiple rootlets of the bulbar root of CNXI. Both the spinal and the bulbar roots combine in the lateral basal cistern and jugular foramen. The spinal root continues as extracranial CNXI to innervate the sternocleidomastoid and trapezius muscles. The bulbar root fibers cross to the vagus nerve extracranially or within the jugular foramen to supply motor innervation to the pharynx (superior constrictor and soft palate) and the larynx (except the cricothyroid muscle).](images/app.statdx.com_image_thumbnail_f43628f4-42a9-4331-8508-079cb8abf634_annotated_false_size_900_quality_90_0f3d98d9cbf882e3b14059ac49cfe28c6658f21a.jpg)
*Graphic of the posterior brainstem reveals both the spinal and the bulbar roots of the accessory nerve (CNXI). Note the lower nucleus ambiguus gives rise to multiple rootlets of the bulbar root of CNXI. Both the spinal and the bulbar roots combine in the lateral basal cistern and jugular foramen. The spinal root continues as extracranial CNXI to innervate the sternocleidomastoid and trapezius muscles. The bulbar root fibers cross to the vagus nerve extracranially or within the jugular foramen to supply motor innervation to the pharynx (superior constrictor and soft palate) and the larynx (except the cricothyroid muscle).*
![Graphic of the posterior brainstem reveals both the spinal and the bulbar roots of the accessory nerve (CNXI). Note the lower nucleus ambiguus gives rise to multiple rootlets of the bulbar root of CNXI. Both the spinal and the bulbar roots combine in the lateral basal cistern and jugular foramen. The spinal root continues as extracranial CNXI to innervate the sternocleidomastoid and trapezius muscles. The bulbar root fibers cross to the vagus nerve extracranially or within the jugular foramen to supply motor innervation to the pharynx (superior constrictor and soft palate) and the larynx (except the cricothyroid muscle).](images/app.statdx.com_image_thumbnail_f43628f4-42a9-4331-8508-079cb8abf634_size_174_quality_85_984f7a75_20251018T124943Z.jpg)
*Graphic of the posterior brainstem reveals both the spinal and the bulbar roots of the accessory nerve (CNXI). Note the lower nucleus ambiguus gives rise to multiple rootlets of the bulbar root of CNXI. Both the spinal and the bulbar roots combine in the lateral basal cistern and jugular foramen. The spinal root continues as extracranial CNXI to innervate the sternocleidomastoid and trapezius muscles. The bulbar root fibers cross to the vagus nerve extracranially or within the jugular foramen to supply motor innervation to the pharynx (superior constrictor and soft palate) and the larynx (except the cricothyroid muscle).*
![Graphic of the posterior brainstem reveals both the spinal and the bulbar roots of the accessory nerve (CNXI). Note the lower nucleus ambiguus gives rise to multiple rootlets of the bulbar root of CNXI. Both the spinal and the bulbar roots combine in the lateral basal cistern and jugular foramen. The spinal root continues as extracranial CNXI to innervate the sternocleidomastoid and trapezius muscles. The bulbar root fibers cross to the vagus nerve extracranially or within the jugular foramen to supply motor innervation to the pharynx (superior constrictor and soft palate) and the larynx (except the cricothyroid muscle).](images/app.statdx.com_image_thumbnail_f43628f4-42a9-4331-8508-079cb8abf634_size_174_quality_85_c19a601e9ca6f6d3b25e5345f5b3296a9a591f11.jpg)
*Graphic of the posterior brainstem reveals both the spinal and the bulbar roots of the accessory nerve (CNXI). Note the lower nucleus ambiguus gives rise to multiple rootlets of the bulbar root of CNXI. Both the spinal and the bulbar roots combine in the lateral basal cistern and jugular foramen. The spinal root continues as extracranial CNXI to innervate the sternocleidomastoid and trapezius muscles. The bulbar root fibers cross to the vagus nerve extracranially or within the jugular foramen to supply motor innervation to the pharynx (superior constrictor and soft palate) and the larynx (except the cricothyroid muscle).*
![Axial graphic shows the upper cervical spinal cord cut to reveal the spinal nucleus of the accessory nerve giving rise to multiple rootlets that unite to form the spinal root of the accessory nerve. The rootlets exit the posterolateral sulcus just anterior to the posterior cervical roots.](images/app.statdx.com_image_thumbnail_9cc5445d-20c9-484c-b739-2fe4ac9254c9_annotated_false_size_900_quality_90_86ba738b37dcca7aefe488089b6d246bedecee37.jpg)
*Axial graphic shows the upper cervical spinal cord cut to reveal the spinal nucleus of the accessory nerve giving rise to multiple rootlets that unite to form the spinal root of the accessory nerve. The rootlets exit the posterolateral sulcus just anterior to the posterior cervical roots.*
### Graphic, Intracranial and Extracranial
![Overview graphic of the intracranial and extracranial accessory nerve (CNXI) shows the lower nucleus ambiguus at the origin of the bulbar root of CNXI, while the spinal nucleus gives rise to the spinal root. Both roots combine in the jugular foramen. Extracranially, the bulbar fibers cross to the vagus nerve to eventually provide motor innervation via the pharyngeal plexus to the soft palate and superior constrictor muscles and via the recurrent laryngeal nerve to the majority of the endolaryngeal muscles. The spinal fibers that remain in the accessory nerve provide motor innervation to the sternocleidomastoid and trapezius muscles. Notice extracranial CNXI runs along the floor of the posterior cervical space.](images/app.statdx.com_image_thumbnail_74edaea2-94e1-434d-8ffb-b2e07cacea20_annotated_false_size_900_quality_90_5f269b61bac14ab5779f4c922d34acd3aa909d00.jpg)
*Overview graphic of the intracranial and extracranial accessory nerve (CNXI) shows the lower nucleus ambiguus at the origin of the bulbar root of CNXI, while the spinal nucleus gives rise to the spinal root. Both roots combine in the jugular foramen. Extracranially, the bulbar fibers cross to the vagus nerve to eventually provide motor innervation via the pharyngeal plexus to the soft palate and superior constrictor muscles and via the recurrent laryngeal nerve to the majority of the endolaryngeal muscles. The spinal fibers that remain in the accessory nerve provide motor innervation to the sternocleidomastoid and trapezius muscles. Notice extracranial CNXI runs along the floor of the posterior cervical space.*
![Axial T2 MR at the level of the medulla shows the bulbar portion of CNXI emerging from the postolivary sulcus just inferior to CNX. The bulbar portion travels anterolaterally through the basal cistern together with CNX and CNIX.](images/app.statdx.com_image_thumbnail_c16e46e6-7c33-4426-95ee-80ffb00e72ff_annotated_false_size_900_quality_90_82aaf47632198fd1a00876ce3abd99c750d0e9ab.jpg)
*Axial T2 MR at the level of the medulla shows the bulbar portion of CNXI emerging from the postolivary sulcus just inferior to CNX. The bulbar portion travels anterolaterally through the basal cistern together with CNX and CNIX.*
![Axial T2 MR through the lower medulla shows the spinal root of CNXI ascending through the foramen magnum to join the bulbar root before entering the pars nervosa of the jugular foramen.](images/app.statdx.com_image_thumbnail_36eec90f-4e31-40aa-9fea-a4ae9f6c42b1_annotated_false_size_900_quality_90_d39e3b420cb1370d69763d61197a7034b8bc9264.jpg)
*Axial T2 MR through the lower medulla shows the spinal root of CNXI ascending through the foramen magnum to join the bulbar root before entering the pars nervosa of the jugular foramen.*
### Axial Bone CT and T2 MR
![Axial bone CT through the jugular foramen shows the anteromedial pars nervosa, the jugular spine, and the posterolateral pars vascularis. The pars nervosa transmits CNIX, the Jacobsen nerve, and the inferior petrosal sinus. The pars vascularis transmits CNX, CNXI, the Arnold nerve, and the sigmoid sinus, which becomes the internal jugular vein.](images/app.statdx.com_image_thumbnail_7f5074e3-c9c6-4537-af19-a6c1f66a8cd4_annotated_false_size_900_quality_90_b92e980dcee473076be45c37fc39e1fede8cca76.jpg)
*Axial bone CT through the jugular foramen shows the anteromedial pars nervosa, the jugular spine, and the posterolateral pars vascularis. The pars nervosa transmits CNIX, the Jacobsen nerve, and the inferior petrosal sinus. The pars vascularis transmits CNX, CNXI, the Arnold nerve, and the sigmoid sinus, which becomes the internal jugular vein.*
![Axial view of a contrast-enhanced MPRAGE sequence shows an enhancing nodule posterior to the left vertebral artery. Enhancing T2-hyperintense small lesions located posterior to the intradural vertebral artery at the foramen magnum have been previously described as benign enhancing foramen magnum lesions (BEFMLs) and recently reported as fibrotic arachnoid nodules adherent to the dorsal aspect of the spinal accessory nerve. On the right side, the nondominant vertebral artery terminates as the posterior inferior cerebellar artery.](3720201b-26ed-4bc2-8604-25c6c17101f6)
*Axial view of a contrast-enhanced MPRAGE sequence shows an enhancing nodule posterior to the left vertebral artery. Enhancing T2-hyperintense small lesions located posterior to the intradural vertebral artery at the foramen magnum have been previously described as benign enhancing foramen magnum lesions (BEFMLs) and recently reported as fibrotic arachnoid nodules adherent to the dorsal aspect of the spinal accessory nerve. On the right side, the nondominant vertebral artery terminates as the posterior inferior cerebellar artery.*
![Axial T2 MR at the same level fails to demonstrate BEFML seen in the contrast-enhanced sequence. BEFMLs are T2 hyperintense and are not identified on routine spin-echo T2-weighted images, as it blends with T2-hyperintense CSF.](d462a1be-0f4f-4f20-abc9-735cbb2c35a2)
*Axial T2 MR at the same level fails to demonstrate BEFML seen in the contrast-enhanced sequence. BEFMLs are T2 hyperintense and are not identified on routine spin-echo T2-weighted images, as it blends with T2-hyperintense CSF.*
### Additional Images
![Axial CECT of an 85-year-old woman with a large paraganglioma of the right jugular foramen who presented with multiple cranial neuropathies (IX-XII) at the level of the hyoid bone shows intravascular tumor within the right internal jugular vein <img src='img/arrows/BS.png' alt='black solid arrow'/>. There is severe atrophy of the trapezius <img src='img/arrows/WS.png' alt='white solid arrow'/> and sternocleidomastoid <img src='img/arrows/WC.png' alt='white curved arrow'/> muscles. There is compensatory enlargement of the right levator scapulae muscle <img src='img/arrows/CC.png' alt='cyan curved arrow'/>, which can mimic a palpable mass on physical exam.](a3c94fce-8bc1-45a6-80b7-1d6f69fc9c67)
*Axial CECT of an 85-year-old woman with a large paraganglioma of the right jugular foramen who presented with multiple cranial neuropathies (IX-XII) at the level of the hyoid bone shows intravascular tumor within the right internal jugular vein <img src='img/arrows/BS.png' alt='black solid arrow'/>. There is severe atrophy of the trapezius <img src='img/arrows/WS.png' alt='white solid arrow'/> and sternocleidomastoid <img src='img/arrows/WC.png' alt='white curved arrow'/> muscles. There is compensatory enlargement of the right levator scapulae muscle <img src='img/arrows/CC.png' alt='cyan curved arrow'/>, which can mimic a palpable mass on physical exam.*
![Axial CT at the level of the thyrohyoid membrane in a 55-year-old woman with chronic denervation injury to the right spinal accessory nerve (that occurred during placement of right ventriculoatrial shunt years earlier) demonstrates marked atrophy of the trapezius <img src='img/arrows/WS.png' alt='white solid arrow'/> and sternocleidomastoid <img src='img/arrows/WC.png' alt='white curved arrow'/> muscles. A catheter is noted in the right internal jugular vein. There is mild hypertrophy of the right levator scapulae muscle <img src='img/arrows/BS.png' alt='black solid arrow'/>.](d983e1d3-1043-4985-b8da-53aa9e19b2f6)
*Axial CT at the level of the thyrohyoid membrane in a 55-year-old woman with chronic denervation injury to the right spinal accessory nerve (that occurred during placement of right ventriculoatrial shunt years earlier) demonstrates marked atrophy of the trapezius <img src='img/arrows/WS.png' alt='white solid arrow'/> and sternocleidomastoid <img src='img/arrows/WC.png' alt='white curved arrow'/> muscles. A catheter is noted in the right internal jugular vein. There is mild hypertrophy of the right levator scapulae muscle <img src='img/arrows/BS.png' alt='black solid arrow'/>.*
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title: "CNXII (Hypoglossal Nerve)"
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---
## TERMINOLOGY
- ### Abbreviations
- Hypoglossal nerve (CNXII)
- ### Synonyms
- 12th cranial nerve, CN12
- ### Definitions
- Motor nerve supplying intrinsic and extrinsic tongue muscles
## IMAGING ANATOMY
- ### Overview
- Motor cranial nerve to intrinsic and extrinsic tongue muscles
- **Palatoglossus**: Only extrinsic muscle **not** innervated by CNXII (but by CNX)
- Hypoglossal nerve anatomic segments
- Intraaxial segment
- Cisternal segment
- Skull base segment
- Extracranial
- ### Intraaxial Segment
- **Hypoglossal nucleus**
- In dorsal medulla, medial to dorsal vagal nucleus
- Long, thin nucleus approximately same length as ventrolateral olive (15- to 18-mm craniocaudal dimension)
- Extends from level of hypoglossal eminence (trigone) in floor of 4th ventricle just inferior to medullary striae of 4th ventricle to proximal medulla
- Hypoglossal intraaxial axonal course
- Efferent fibers from hypoglossal nucleus extend ventrally through medulla, lateral to medial lemniscus
- Efferent fibers exit between olivary nucleus and pyramid (root exit zone) at **ventrolateral sulcus** (a.k.a. **preolivary sulcus)**
- ### Cisternal Segment
- Efferent fibers coalesce to form multiple (6-14) **rootlets**
- In premedullary cistern, course between posterior inferior cerebellar artery and vertebral artery
- Rootlets fuse into hypoglossal nerve (2-4 trunks) as it exits skull base through hypoglossal canal
- Hypoglossal filaments may merge with vagal fibers
- Total length of cisternal segment ranges from 8-15 mm; mean width of cisternal segment ranges from 0.3-0.6 mm
- ### Skull Base Segment
- Hypoglossal nerve exits occipital bone via **hypoglossal canal**, surrounded by venous plexus
- Canal in occipital bone caudal to jugular foramen
- "Empties" into medial nasopharyngeal carotid space
- Osseous septa may bisect hypoglossal canal
- Mean length of hypoglossal canal ranges from 9.5-16.0 mm; mean width ranges from 1.3-3.0 mm
- ### Extracranial Segment
- **Carotid space component****of CNXII**
- Hypoglossal canal "empties" into medial nasopharyngeal carotid space
- Hypoglossal nerve immediately gives off **dural branches** after exiting hypoglossal canal
- Descends in posterior carotid space, closely apposed with CNX
- Exits carotid space anteriorly between jugular vein and internal carotid artery, crosses lateral surface of external carotid artery at inferior margin of posterior belly of digastric muscle
- **Transspatial component****of CNXII**
- From carotid space, nerve runs anteroinferiorly toward hyoid bone, lateral to carotid bifurcation
- At level of occipital artery base, nerve turns anterior, continuing as muscular branch below posterior belly of digastric muscle, medial to submandibular gland
- Gives off superior root of ansa cervicalis from horizontal segment of nerve to anastomose with lower root
- Distal branches of imaging importance
- **Muscular branch** travels on lateral margin of hyoglossus muscle in posterior sublingual space close to lingual artery, medial to mylohyoid muscle
- Innervates extrinsic (styloglossus, hyoglossus, and genioglossus) and intrinsic tongue muscles
- **Geniohyoid**innervated by **C1** spinal nerve
- **Ansa cervicalis**: Formed from superior and inferior (C1-C3 spinal nerves) roots
- Innervates infrahyoid strap muscles (sternothyroid, sternohyoid, omohyoid)
- Difficult to directly identify nerve extracranially; position inferred by adjacent anatomical structures
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- MR preferred study: Best for brainstem, cisterns, skull base, and suprahyoid neck
- Should include heavily T2-weighted sequence
- CECT of suprahyoid neck (cover from orbital roof to below hyoid) with bone algorithm of skull base
- ### Imaging Sweet Spots
- Include nerve from brainstem to hyoid bone
- Asymmetric appearance of tongue gives clue to denervation
- Acute/subacute: Denervated hemitongue may show low T1 and high T2 intensity with enhancement
- Chronic: Tongue atrophy (fatty infiltration and volume loss); infrahyoid strap muscle atrophy
- ### Imaging Pitfalls
- Denervated hemitongue may appear enlarged due to edema (acute) or flaccidity (chronic); may mimic infiltrative tongue mass
- Not imaging hyoid bone will result in missed diagnoses
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Unilateral lesion causes tongue protrusion to "side of lesion"
- Nearly 50% of CNXII neuropathies from neoplastic processes, mostly malignant
- Rare, persistent, primitive hypoglossal artery arises from cervical internal carotid artery C1-C2 level and passes through hypoglossal canal into posterior fossa; anastomoses with vertebrobasilar system
1d99f80b-a4f5-4f15-84bf-e38f6e38c5c4
## Images
### Graphics, Intracranial
![Graphic of the lower brainstem seen from behind illustrates key features of the proximal hypoglossal nerve. Notice the hypoglossal nucleus in the dorsal paramedian medulla feeding intraaxial axons that exit the preolivary sulcus into the anterolateral basal cistern. Cisternal rootlets fuse into the hypoglossal nerve that traverses the skull base through the hypoglossal canal. Exiting the hypoglossal canal, CNXII immediately enters the nasopharyngeal carotid space.](images/app.statdx.com_image_thumbnail_4635bc83-dbf5-4e71-baae-8621b5e15184_annotated_false_size_900_quality_90_cf1331df2aa3bcfa5f7474ef50d5facba58a93e5.jpg)
*Graphic of the lower brainstem seen from behind illustrates key features of the proximal hypoglossal nerve. Notice the hypoglossal nucleus in the dorsal paramedian medulla feeding intraaxial axons that exit the preolivary sulcus into the anterolateral basal cistern. Cisternal rootlets fuse into the hypoglossal nerve that traverses the skull base through the hypoglossal canal. Exiting the hypoglossal canal, CNXII immediately enters the nasopharyngeal carotid space.*
![Graphic of the lower brainstem seen from behind illustrates key features of the proximal hypoglossal nerve. Notice the hypoglossal nucleus in the dorsal paramedian medulla feeding intraaxial axons that exit the preolivary sulcus into the anterolateral basal cistern. Cisternal rootlets fuse into the hypoglossal nerve that traverses the skull base through the hypoglossal canal. Exiting the hypoglossal canal, CNXII immediately enters the nasopharyngeal carotid space.](images/app.statdx.com_image_thumbnail_4635bc83-dbf5-4e71-baae-8621b5e15184_size_174_quality_85_d29165f77349f9dc1ed946ba3cd8cf4f851144ff.jpg)
*Graphic of the lower brainstem seen from behind illustrates key features of the proximal hypoglossal nerve. Notice the hypoglossal nucleus in the dorsal paramedian medulla feeding intraaxial axons that exit the preolivary sulcus into the anterolateral basal cistern. Cisternal rootlets fuse into the hypoglossal nerve that traverses the skull base through the hypoglossal canal. Exiting the hypoglossal canal, CNXII immediately enters the nasopharyngeal carotid space.*
![Axial graphic through the lower medulla shows the hypoglossal nucleus feeding intraaxial axons that dive ventrally to curve around the inferior olivary nucleus to exit the medulla ventrolaterally via the preolivary sulcus. Note that the hypoglossal nucleus gives the floor of the 4th ventricle an arch (hypoglossal eminence/trigone). The cisternal rootlets combine in the hypoglossal canal to become the hypoglossal nerve (CNXII). Note the hypoglossal canal is anterior and inferior to the jugular foramen.](images/app.statdx.com_image_thumbnail_b35dcbd5-ddfa-4978-a8a2-d70a8de1df05_annotated_false_size_900_quality_90_34fb683f7ebc6d6c01b15a039f3e0feffc0d513f.jpg)
*Axial graphic through the lower medulla shows the hypoglossal nucleus feeding intraaxial axons that dive ventrally to curve around the inferior olivary nucleus to exit the medulla ventrolaterally via the preolivary sulcus. Note that the hypoglossal nucleus gives the floor of the 4th ventricle an arch (hypoglossal eminence/trigone). The cisternal rootlets combine in the hypoglossal canal to become the hypoglossal nerve (CNXII). Note the hypoglossal canal is anterior and inferior to the jugular foramen.*
### Graphic, Extracranial
![Lateral graphic depicts the entire course of the hypoglossal nerve. The nerve originates in the hypoglossal nucleus in the floor of the 4th ventricle. As CNXII exits the skull base, it immediately enters the nasopharyngeal carotid space just medial to the internal carotid artery. It travels inferiorly in the carotid space to exit anteriorly between the carotid artery and the internal jugular vein. CNXII supplies motor innervation to intrinsic and extrinsic (styloglossus, hyoglossus, genioglossus) tongue muscles. C1 spinal nerve supplies motor to the geniohyoid muscle. Ansa cervicalis (C1-C3 spinal nerves) supplies motor innervation to the infrahyoid strap muscles, including sternothyroid, sternohyoid, and omohyoid muscles. Also note the meningeal sensory branch from C1 following CNXII retrograde to supply clival meninges.](images/app.statdx.com_image_thumbnail_c7927fe9-4ce0-4a89-8df3-332ad6be44ec_annotated_false_size_900_quality_90_463bea1d73dc70fee19cb059c65afe842bbdf644.jpg)
*Lateral graphic depicts the entire course of the hypoglossal nerve. The nerve originates in the hypoglossal nucleus in the floor of the 4th ventricle. As CNXII exits the skull base, it immediately enters the nasopharyngeal carotid space just medial to the internal carotid artery. It travels inferiorly in the carotid space to exit anteriorly between the carotid artery and the internal jugular vein. CNXII supplies motor innervation to intrinsic and extrinsic (styloglossus, hyoglossus, genioglossus) tongue muscles. C1 spinal nerve supplies motor to the geniohyoid muscle. Ansa cervicalis (C1-C3 spinal nerves) supplies motor innervation to the infrahyoid strap muscles, including sternothyroid, sternohyoid, and omohyoid muscles. Also note the meningeal sensory branch from C1 following CNXII retrograde to supply clival meninges.*
### Axial T2 MR
![Superior of 2 axial T2 MR images in the same patient through the lower medulla demonstrates the origin of hypoglossal nerves from the preolivary sulcus. The nerves arise as rootlets that coalesce into 2-4 trunks, which exit through the hypoglossal canal. The trunks abut or pass near the vertebral arteries in the basal cisterns.](images/app.statdx.com_image_thumbnail_d5fbec27-7a23-4268-ab1d-8733d9c7cb85_annotated_false_size_900_quality_90_b036727f430cbb89649c9be66397d52934df7c13.jpg)
*Superior of 2 axial T2 MR images in the same patient through the lower medulla demonstrates the origin of hypoglossal nerves from the preolivary sulcus. The nerves arise as rootlets that coalesce into 2-4 trunks, which exit through the hypoglossal canal. The trunks abut or pass near the vertebral arteries in the basal cisterns.*
![Second axial MR at the lower medulla shows the cisternal segments of bilateral hypoglossal nerves after they emerge from the medulla in the preolivary sulcus as rootlets. Rootlets on either side fuse into the corresponding side hypoglossal nerve and exit the skull base through the hypoglossal canal. Close proximity of these rootlets with the vertebral arteries is seen in this view.](images/app.statdx.com_image_thumbnail_e0cc0ae5-6e6d-4f94-87d2-87ac3face246_annotated_false_size_900_quality_90_407f4bac17fa8e7d53b086f42a5abcd31186488a.jpg)
*Second axial MR at the lower medulla shows the cisternal segments of bilateral hypoglossal nerves after they emerge from the medulla in the preolivary sulcus as rootlets. Rootlets on either side fuse into the corresponding side hypoglossal nerve and exit the skull base through the hypoglossal canal. Close proximity of these rootlets with the vertebral arteries is seen in this view.*
![Axial heavily T2-weighted MR in another patient through the lower medulla demonstrates a cisternal rootlet on the left from the origin to the hypoglossal canal. Note the hypoglossal canal on the right seen with an intermediate signal intensity.](7ef1db37-6450-4baf-90b3-494ee9a0b7b4)
*Axial heavily T2-weighted MR in another patient through the lower medulla demonstrates a cisternal rootlet on the left from the origin to the hypoglossal canal. Note the hypoglossal canal on the right seen with an intermediate signal intensity.*
### Coronal Bone CT
![First of 3 coronal bone CT images presented from posterior to anterior shows the hypoglossal canal as a complete bony circle, indicating that the image is at the level of the entry into the canal. The location of CNXII is in the upper medial quadrant within the hypoglossal canal.](1516a577-f69b-4d43-be20-6654f44c972d)
*First of 3 coronal bone CT images presented from posterior to anterior shows the hypoglossal canal as a complete bony circle, indicating that the image is at the level of the entry into the canal. The location of CNXII is in the upper medial quadrant within the hypoglossal canal.*
![In this image of the midhypoglossal canal, the surrounding bone appears as a &quot;bird's head and beak&quot; with the head and beak made up of the jugular tubercle. The jugular foramen is directly lateral to the hypoglossal canal.](f0badeed-043f-4b28-a217-835e5b4ce9c8)
*In this image of the midhypoglossal canal, the surrounding bone appears as a &quot;bird's head and beak&quot; with the head and beak made up of the jugular tubercle. The jugular foramen is directly lateral to the hypoglossal canal.*
![At the level of the distal hypoglossal canal, the hypoglossal nerve leaves the skull base to emerge inferiorly into the nasopharyngeal carotid space. Notice the lateral jugular foramen also empties its contents into the carotid space, including the jugular vein and cranial nerves IX, X, and XI.](86ac03fa-268d-448b-a7a8-90465a700944)
*At the level of the distal hypoglossal canal, the hypoglossal nerve leaves the skull base to emerge inferiorly into the nasopharyngeal carotid space. Notice the lateral jugular foramen also empties its contents into the carotid space, including the jugular vein and cranial nerves IX, X, and XI.*
### Coronal T1 C+ MR
![First of 3 sequential coronal T1 C+ MR images presented from posterior to anterior is shown. In this MR, the hypoglossal nerve is seen entering the proximal hypoglossal canal. The hypointense hypoglossal nerve is surrounded by the strongly enhancing venous plexus and is therefore easily seen on thin-section enhanced MR. The hypoglossal canal also carries a branch of the ascending pharyngeal artery.](6872ea47-5fac-447f-ac21-6bd7e636e672)
*First of 3 sequential coronal T1 C+ MR images presented from posterior to anterior is shown. In this MR, the hypoglossal nerve is seen entering the proximal hypoglossal canal. The hypointense hypoglossal nerve is surrounded by the strongly enhancing venous plexus and is therefore easily seen on thin-section enhanced MR. The hypoglossal canal also carries a branch of the ascending pharyngeal artery.*
![In this coronal MR of the midhypoglossal canal, the low-signal hypoglossal nerve is visible surrounded by the enhancing venous plexus just beneath the &quot;bird's beak&quot; of the jugular tubercle.](e4e9e7f2-0a18-49c5-9238-6adfc47126c3)
*In this coronal MR of the midhypoglossal canal, the low-signal hypoglossal nerve is visible surrounded by the enhancing venous plexus just beneath the &quot;bird's beak&quot; of the jugular tubercle.*
![In this coronal MR through the distal hypoglossal canal, the hypoglossal nerves can be seen exiting inferolaterally into the nasopharyngeal carotid space. Notice also the internal jugular vein exiting inferiorly on the patient's right into this same nasopharyngeal carotid space.](e9a16835-5dd6-4b4e-8181-ab27ed3aa7d9)
*In this coronal MR through the distal hypoglossal canal, the hypoglossal nerves can be seen exiting inferolaterally into the nasopharyngeal carotid space. Notice also the internal jugular vein exiting inferiorly on the patient's right into this same nasopharyngeal carotid space.*
### Axial Bone CT and CTA
![Axial bone CT at the level of the hypoglossal canal is shown. Notice the margins of the hypoglossal canals are well corticated.](f4236863-79e1-43c2-85e1-c1a65f3918bb)
*Axial bone CT at the level of the hypoglossal canal is shown. Notice the margins of the hypoglossal canals are well corticated.*
![Axial CTA through the skull base demonstrates a persistent carotid basilar connection, a persistent hypoglossal artery traversing the left hypoglossal canal. The normal right hypoglossal canal can also be seen.](d37c29ac-3b5d-4156-83a3-ebc47ed6faa2)
*Axial CTA through the skull base demonstrates a persistent carotid basilar connection, a persistent hypoglossal artery traversing the left hypoglossal canal. The normal right hypoglossal canal can also be seen.*
### Pathology
![Coronal T1 FS MR demonstrates a heterogeneously enhancing skull base mass along the right jugular foramen. Note the smooth erosion of the right lateral jugular tubercle (&quot;bird's beak&quot;) and the intact hypoglossal canal with the nerve below the &quot;bird's beak.&quot;](72e8125c-4cdc-44fd-937e-af25392af7d7)
*Coronal T1 FS MR demonstrates a heterogeneously enhancing skull base mass along the right jugular foramen. Note the smooth erosion of the right lateral jugular tubercle (&quot;bird's beak&quot;) and the intact hypoglossal canal with the nerve below the &quot;bird's beak.&quot;*
![Coronal T1 FS MR demonstrates abnormal leptomeningeal enhancement, including leptomeningeal spread along the left hypoglossal nerve cisternal segment entering into the hypoglossal canal. Again note abnormal leptomeningeal enhancement seen along bilateral jugular foramina above the &quot;bird's beaks.&quot;](d2aeb3be-560f-44dc-b235-6c26184fba11)
*Coronal T1 FS MR demonstrates abnormal leptomeningeal enhancement, including leptomeningeal spread along the left hypoglossal nerve cisternal segment entering into the hypoglossal canal. Again note abnormal leptomeningeal enhancement seen along bilateral jugular foramina above the &quot;bird's beaks.&quot;*
### Additional Images
![First of 2 axial T2 MR images through the lower medulla demonstrates the cisternal segment of hypoglossal nerves. Anatomy of the cisternal segment is variable, but usually multiple rootlets emerge from the preolivary sulcus and merge into 2 trunks, which penetrate the dura to enter the hypoglossal canal. The trunks abut or pass near the vertebral arteries in the basal cisterns.](bcfcf922-e7f3-41b9-9798-1ba87582a82f)
*First of 2 axial T2 MR images through the lower medulla demonstrates the cisternal segment of hypoglossal nerves. Anatomy of the cisternal segment is variable, but usually multiple rootlets emerge from the preolivary sulcus and merge into 2 trunks, which penetrate the dura to enter the hypoglossal canal. The trunks abut or pass near the vertebral arteries in the basal cisterns.*
![Hypoglossal nerves emerge from the medulla in the preolivary sulcus between the olive and pyramid. Cisternal segment of the patient's left hypoglossal nerve is seen as a thick, discrete trunk entering the hypoglossal canal. The right hypoglossal nerve consists of multiple small rootlets.](141bf3fe-4e37-485b-aa5a-07442bc44a0a)
*Hypoglossal nerves emerge from the medulla in the preolivary sulcus between the olive and pyramid. Cisternal segment of the patient's left hypoglossal nerve is seen as a thick, discrete trunk entering the hypoglossal canal. The right hypoglossal nerve consists of multiple small rootlets.*
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---
title: "Cranial Nerves Overview"
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value: "Surjith Vattoth, MD"
- key: "33151213-01b2-4542-9105-342e006b3915"
value: "H. Ric Harnsberger, MD"
- key: "94f835c8-fa13-4e8a-995b-53048e6b0605"
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pageDescription: "Cranial Nerves Overview"
pageKeywords: "Head and Neck, Anatomy, Cranial Nerves, Cranial Nerves Overview"
pageTitle: "Cranial Nerves Overview | STATdx"
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---
## TERMINOLOGY
- ### Synonyms
- Olfactory nerve: CNI
- Optic nerve: CNII
- Oculomotor nerve: CNIII
- Trochlear nerve: CNIV
- Trigeminal nerve: CNV
- Abducens nerve: CNVI
- Facial nerve: CNVII
- Vestibulocochlear nerve: CNVIII
- Glossopharyngeal nerve: CNIX
- Vagus nerve: CNX
- Accessory nerve: CNXI
- Hypoglossal nerve: CNXII
## IMAGING ANATOMY
- ### Overview
- Cranial nerve groupings based on area of brainstem origin
- Diencephalon: CNII
- Mesencephalon (midbrain): CNIII and CNIV
- Pons: CNV, CNVI, CNVII, and CNVIII
- Medulla: CNIX, CNX, CNXI, and CNXII
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Best imaging modality for any simple or complex cranial neuropathy: **MR**
- Single exception to this directive is distal vagal neuropathy where imaging down to aortopulmonic window on left is necessary
- CECT better here, as less affected by breathing, swallowing, and coughing movements
- If lesion located in bony area, such as skull base, sinuses, or mandible, bone CT highly recommended to provide complementary bone anatomy and lesion-related information
- Contrast enhancement of CT not necessary if full T1, T2, and T1 C+ MR available
- ### Imaging Approaches
- Remember: Cranial nerves do**not**stop at skull base
- Radiologist must image entire extent of affected cranial nerve
- **CNI, CNII, CNIII, CNIV, and CNVI**: Include focused **orbital sequences**
- **CNV**: Include entire **face to****inferior mandible if V3** affected
- **CNVII**: Include **cerebellopontine angle (****CPA), temporal bone, and parotid space**
- **CNVIII**: Include **CPA-internal auditory canal (IAC) and inner ear**
- **CNIX-XII**: Include **basal cistern, skull base, nasopharyngeal carotid space**
- **CNX**: To fully evaluate for recurrent laryngeal nerve lesion, follow carotid space to just below aortopulmonic window on left and subclavian artery on right
- **CNXII**: Remember to reach hyoid bone to include distal loop as it rises into sublingual space
- ### Imaging Pitfalls
- Radiologist forgets to image extracranial structures associated with cranial nerve affected
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Cranial nerves and their functions
- Olfactory nerve (CNI)
- Sense of **smell**
- Optic nerve (CNII)
- Sense of **vision**
- Oculomotor nerve (CNIII)
- **Motor** to all **extraocular muscles** except lateral rectus and superior oblique
- **Parasympathetic** supply to ciliary and pupillary constrictor muscles
- Trochlear nerve (CNIV)
- **Motor** to **superior oblique**muscle
- Trigeminal nerve (CNV)
- **Motor** (V3) to **muscles of mastication**, anterior belly digastric, mylohyoid, tensor tympani and palatini
- **Sensory** innervation to surface of **forehead and nose** (V1), **cheek**(V2), and**jaw** (V3)
- **Sensory** innervation to surfaces of nose, sinuses, meninges, and external surface of tympanic membrane (auriculotemporal nerve)
- Abducens nerve (CNVI)
- **Motor** to **lateral rectus** muscle
- Facial nerve (CNVII)
- **Motor** to **muscles of facial expression**
- **Motor** to **stapedius muscle**
- **Parasympathetic** to lacrimal, submandibular, and sublingual glands
- Anterior 2/3 tongue **taste** (chorda tympanic nerve)
- General sensation for periauricular skin, external surface of tympanic membrane
- Vestibulocochlear nerve (CNVIII)
- Senses of **hearing and balance**
- Glossopharyngeal nerve (CNIX)
- **Motor** to **stylopharyngeus** muscle
- **Parasympathetic** to parotid gland
- Visceral sensory innervation to carotid body
- Posterior 1/3 tongue **taste**
- General sensation to posterior 1/3 of tongue and internal surface of tympanic membrane
- Vagus nerve (CNX)
- **Motor** to **pharynx-larynx**
- Parasympathetic to pharynx, larynx, thoracic and abdominal viscera
- Visceral sensation from pharynx, larynx, and viscera
- General sensation from small area around external ear
- Accessory nerve (CNXI)
- **Motor** to **sternocleidomastoid and trapezius** muscles
- Hypoglossal nerve (CNXII)
- **Motor** to intrinsic and extrinsic **tongue muscles** except palatoglossus
8f0f497e-0a2a-42b2-abc7-8a11bc746b8e
## Images
### Graphics, Global Cranial Nerves
![Graphic shows all cranial nerves, viewing the brainstem from below. Remember that CNIII-IV are associated with the midbrain (mesencephalon), while CNV-VIII are affiliated with the pons. CNIX-XII emerge from various aspects of the medulla.](images/app.statdx.com_image_thumbnail_d804fef5-6a33-4524-b853-04bdab81a88d_annotated_false_size_900_quality_90_cc8e15933e8aec03cedeb03181e231dddb9e1bd1.jpg)
*Graphic shows all cranial nerves, viewing the brainstem from below. Remember that CNIII-IV are associated with the midbrain (mesencephalon), while CNV-VIII are affiliated with the pons. CNIX-XII emerge from various aspects of the medulla.*
![Graphic shows all cranial nerves, viewing the brainstem from below. Remember that CNIII-IV are associated with the midbrain (mesencephalon), while CNV-VIII are affiliated with the pons. CNIX-XII emerge from various aspects of the medulla.](images/app.statdx.com_image_thumbnail_d804fef5-6a33-4524-b853-04bdab81a88d_size_174_quality_85_5eb8e060d9bbdf4fa548c9f4fd2c885791e2da82.jpg)
*Graphic shows all cranial nerves, viewing the brainstem from below. Remember that CNIII-IV are associated with the midbrain (mesencephalon), while CNV-VIII are affiliated with the pons. CNIX-XII emerge from various aspects of the medulla.*
![Graphic shows all cranial nerves, viewing the brainstem from below. Remember that CNIII-IV are associated with the midbrain (mesencephalon), while CNV-VIII are affiliated with the pons. CNIX-XII emerge from various aspects of the medulla.](images/app.statdx.com_image_thumbnail_d804fef5-6a33-4524-b853-04bdab81a88d_size_174_quality_85_ccf5e1e0_20251018T124943Z.jpg)
*Graphic shows all cranial nerves, viewing the brainstem from below. Remember that CNIII-IV are associated with the midbrain (mesencephalon), while CNV-VIII are affiliated with the pons. CNIX-XII emerge from various aspects of the medulla.*
![In this graphic of the skull base, viewed from above, the foramina are illustrated on the right, and the associated cranial nerves are illustrated on the left. The terminal branches of CNI exit the skull base through many openings in the cribriform plate of the ethmoid bone. CNII exits via the optic canal, while CNIII, CNIV, CNVI, and CNV1 all go through the superior orbital fissure. V2 traverses foramen rotundum, and V3 is seen exiting the foramen ovale. CNVII and CNVIII are seen in the internal auditory canal with CNIX-XI found in the jugular foramen. Finally, CNXII uses its own hypoglossal canal to leave the basal cistern.](images/app.statdx.com_image_thumbnail_47e92f3e-65bf-43e1-b343-8ace3a3fb621_annotated_false_size_900_quality_90_8e269de1a97d664e3e152a548bff1be1f68ce7e6.jpg)
*In this graphic of the skull base, viewed from above, the foramina are illustrated on the right, and the associated cranial nerves are illustrated on the left. The terminal branches of CNI exit the skull base through many openings in the cribriform plate of the ethmoid bone. CNII exits via the optic canal, while CNIII, CNIV, CNVI, and CNV1 all go through the superior orbital fissure. V2 traverses foramen rotundum, and V3 is seen exiting the foramen ovale. CNVII and CNVIII are seen in the internal auditory canal with CNIX-XI found in the jugular foramen. Finally, CNXII uses its own hypoglossal canal to leave the basal cistern.*
### Graphics, Upper Cranial Nerves
![Axial graphic shows the prepontine cistern and cavernous sinus (CS) areas viewed from above. The preganglionic segment of CNV can be seen in the lateral prepontine cistern, entering the Meckel cave through the porus trigeminus.](images/app.statdx.com_image_thumbnail_a1bdb18f-e752-4eec-b5ca-b4f27fca2c42_annotated_false_size_900_quality_90_59f5fbe2b8e0015f8a57fcec2db2d427acf4c66a.jpg)
*Axial graphic shows the prepontine cistern and cavernous sinus (CS) areas viewed from above. The preganglionic segment of CNV can be seen in the lateral prepontine cistern, entering the Meckel cave through the porus trigeminus.*
![Coronal posterior graphic of CS is shown. Abducens nerve (CNVI) is the only cranial nerve with a purely intracavernous course. Thick inner endosteal layer of CS lateral wall envelops CNIII, CNIV, CNV1, and CNV2. CNIII and CNIV enter the roof of CS. CNIII travels a short distance in a tubular CSF-containing cistern before becoming incorporated into the lateral wall of CS. CNIV becomes immediately embedded in the lateral wall. CNV1 also lies in lateral wall. CNV2 lies at inferior margin of CS lateral wall or just outside CS envelope. CNV3 is invested by contiguous dura but not considered component of CS wall. Sympathetic nerves travel along the intracavernous internal carotid artery (ICA) as well.](images/app.statdx.com_image_thumbnail_8fed18a8-6631-4db7-9f8f-54608a08cabf_annotated_false_size_900_quality_90_7bbb2503475260bdc8597c508dee5d58cb022c62.jpg)
*Coronal posterior graphic of CS is shown. Abducens nerve (CNVI) is the only cranial nerve with a purely intracavernous course. Thick inner endosteal layer of CS lateral wall envelops CNIII, CNIV, CNV1, and CNV2. CNIII and CNIV enter the roof of CS. CNIII travels a short distance in a tubular CSF-containing cistern before becoming incorporated into the lateral wall of CS. CNIV becomes immediately embedded in the lateral wall. CNV1 also lies in lateral wall. CNV2 lies at inferior margin of CS lateral wall or just outside CS envelope. CNV3 is invested by contiguous dura but not considered component of CS wall. Sympathetic nerves travel along the intracavernous internal carotid artery (ICA) as well.*
![Axial graphic shows that CNIII passes in between the posterior cerebral artery (PCA) and superior cerebellar artery (SCA) near the arterial origins. CNIV also passes between PCA and SCA but more laterally in the perimesencephalic cistern.](images/app.statdx.com_image_thumbnail_6ec43d5e-e6fb-4b3a-b900-10c1f63b09d7_annotated_false_size_900_quality_90_f397b83a806b48008d6a462a72736a807d2a25c6.jpg)
*Axial graphic shows that CNIII passes in between the posterior cerebral artery (PCA) and superior cerebellar artery (SCA) near the arterial origins. CNIV also passes between PCA and SCA but more laterally in the perimesencephalic cistern.*
### Graphics, Lower Cranial Nerves
![Graphic shows frontal view of brainstem and exiting cranial nerves. CNIII is seen exiting the midbrain into the interpeduncular cistern. CNIV wraps around lateral midbrain in tentorial margin. CNVI exits at pontomedullary junction. CNVII and CNVIII exit brainstem at cerebellopontine angle. Inferiorly, CNIX-XI leave the lateral medulla in the postolivary sulcus. CNXII exits via the preolivary sulcus.](images/app.statdx.com_image_thumbnail_8349a260-d92b-4d15-b9fa-5431188a0f85_annotated_false_size_900_quality_90_45dc180738fa2857a518ad0c52b9d470b3decdcc.jpg)
*Graphic shows frontal view of brainstem and exiting cranial nerves. CNIII is seen exiting the midbrain into the interpeduncular cistern. CNIV wraps around lateral midbrain in tentorial margin. CNVI exits at pontomedullary junction. CNVII and CNVIII exit brainstem at cerebellopontine angle. Inferiorly, CNIX-XI leave the lateral medulla in the postolivary sulcus. CNXII exits via the preolivary sulcus.*
![Graphic shows brainstem from behind, emphasizing lower cranial nerve nuclei. On the right are efferent fibers, and on the left are afferent fibers connecting to brainstem nuclei. Note nucleus ambiguus providing voluntary motor fibers to CNIX and CNX. Pontine superior salivatory nucleus provides parasympathetic supply functionally through facial nerve/chorda tympani to submandibular ganglion (topographically hanging down from lingual nerve) and through facial nerve/vidian nerve to pterygopalatine ganglion (topographically hanging down from maxillary nerve). Inferior salivatory nucleus provides secretomotor fibers to the parotid via CNIX. Dorsal motor nucleus provides involuntary motor and sensory fibers to CNX. Solitary tract receives taste from CNVII and CNIX.](d974dc8d-1bb8-4649-bb2b-59769be54160)
*Graphic shows brainstem from behind, emphasizing lower cranial nerve nuclei. On the right are efferent fibers, and on the left are afferent fibers connecting to brainstem nuclei. Note nucleus ambiguus providing voluntary motor fibers to CNIX and CNX. Pontine superior salivatory nucleus provides parasympathetic supply functionally through facial nerve/chorda tympani to submandibular ganglion (topographically hanging down from lingual nerve) and through facial nerve/vidian nerve to pterygopalatine ganglion (topographically hanging down from maxillary nerve). Inferior salivatory nucleus provides secretomotor fibers to the parotid via CNIX. Dorsal motor nucleus provides involuntary motor and sensory fibers to CNX. Solitary tract receives taste from CNVII and CNIX.*
### Axial Bone CT
![First of 6 sequential axial bone CT images through the skull base, presented from inferior to superior, shows foramina of sphenoid bone, including foramen rotundum (CNV2) and foramen ovale (CNV3). More posteriorly oblique, the hypoglossal canal is visible bilaterally in the occipital bone.](f534b355-2a6b-45a3-aec1-e0b3a4da4af0)
*First of 6 sequential axial bone CT images through the skull base, presented from inferior to superior, shows foramina of sphenoid bone, including foramen rotundum (CNV2) and foramen ovale (CNV3). More posteriorly oblique, the hypoglossal canal is visible bilaterally in the occipital bone.*
![At the level of the inferior jugular foramen, the entry to the vertical segment of the carotid canal is also seen just anterior to the jugular foramen. Notice the ovoid shape of the jugular foramen at this level. The floor of the anteromedial aspect of the horizontal segment of the petrous ICA is called the foramen lacerum.](8317f194-f15e-45ee-a23d-1dee2ad59f34)
*At the level of the inferior jugular foramen, the entry to the vertical segment of the carotid canal is also seen just anterior to the jugular foramen. Notice the ovoid shape of the jugular foramen at this level. The floor of the anteromedial aspect of the horizontal segment of the petrous ICA is called the foramen lacerum.*
![At the level of the cribriform plate, the jugular foramen is now divided by the jugular spine into the more anterior pars nervosa (CNIX, Jacobsen nerve, and the inferior petrosal sinus) and more posterolateral pars vascularis (CNX, CNXI, Arnold nerve, and jugular bulb).](241951fc-61a0-46d1-836b-044d126b4eff)
*At the level of the cribriform plate, the jugular foramen is now divided by the jugular spine into the more anterior pars nervosa (CNIX, Jacobsen nerve, and the inferior petrosal sinus) and more posterolateral pars vascularis (CNX, CNXI, Arnold nerve, and jugular bulb).*
![At the level of the midhorizontal portion of the petrous ICA, the superior orbital fissure is seen. Remember that CNIII, CNIV, and CNVI as well as the ophthalmic division of CNV and the superior ophthalmic vein all enter the orbit through this structure.](83a64e0d-e71f-40d1-8d84-f0f6becc23b2)
*At the level of the midhorizontal portion of the petrous ICA, the superior orbital fissure is seen. Remember that CNIII, CNIV, and CNVI as well as the ophthalmic division of CNV and the superior ophthalmic vein all enter the orbit through this structure.*
![At the level of the cochlea and upper petrous apex, the petrooccipital fissure is seen. This is approximately the location of CNVI after it pierces the dura to leave the prepontine cistern on its way to the CS. On bone CT, the area of the CS can only be approximated. Notice also the inferior margin of the porus trigeminus.](a842c44d-0f33-4631-917d-1e410de9f4ec)
*At the level of the cochlea and upper petrous apex, the petrooccipital fissure is seen. This is approximately the location of CNVI after it pierces the dura to leave the prepontine cistern on its way to the CS. On bone CT, the area of the CS can only be approximated. Notice also the inferior margin of the porus trigeminus.*
![The internal auditory canal is visible on this most cephalad CT. The facial (CNVII) and vestibulocochlear (CNVIII) nerves pass through the internal auditory canal. The optic nerve (CNII) enters orbit via the optic canal, which lies medial to the anterior clinoid process.](b5fe070f-9193-4d06-ae3f-f81a5c341ef0)
*The internal auditory canal is visible on this most cephalad CT. The facial (CNVII) and vestibulocochlear (CNVIII) nerves pass through the internal auditory canal. The optic nerve (CNII) enters orbit via the optic canal, which lies medial to the anterior clinoid process.*
### Axial T2 MR
![First of 12 axial T2 MR images presented from inferior to superior shows the left hypoglossal nerve leaving the preolivary sulcus of the medulla. Spinal root of accessory nerve (CNXI) ascends through the foramen magnum, lateral to the brainstem, to unite with the cranial roots of the accessory nerve before exiting via the jugular foramen.](e2415fb7-3a69-4881-9e49-ca450a78a285)
*First of 12 axial T2 MR images presented from inferior to superior shows the left hypoglossal nerve leaving the preolivary sulcus of the medulla. Spinal root of accessory nerve (CNXI) ascends through the foramen magnum, lateral to the brainstem, to unite with the cranial roots of the accessory nerve before exiting via the jugular foramen.*
![Glossopharyngeal (CNIX), vagus (CNX), and cranial (bulbar) roots of spinal accessory (CNXI) nerves emerge from lateral brainstem posterior to the olive in the postolivary sulcus and exit the skull base via jugular foramen. Do not confuse the posterior or anterior inferior cerebellar arteries for cranial nerves.](4205d8f6-d767-4740-bd57-43c62395eec9)
*Glossopharyngeal (CNIX), vagus (CNX), and cranial (bulbar) roots of spinal accessory (CNXI) nerves emerge from lateral brainstem posterior to the olive in the postolivary sulcus and exit the skull base via jugular foramen. Do not confuse the posterior or anterior inferior cerebellar arteries for cranial nerves.*
![Nucleus of hypoglossal nerve (CNXII) forms a characteristic bulge on the floor of the 4th ventricle called the hypoglossal trigone. It is often difficult to separate CNIX from CNX in the basal cistern.](fd3d13b0-561f-40a6-a45d-20d19a59f8f5)
*Nucleus of hypoglossal nerve (CNXII) forms a characteristic bulge on the floor of the 4th ventricle called the hypoglossal trigone. It is often difficult to separate CNIX from CNX in the basal cistern.*
![Abducens (CNVI) nerves exit the brainstem anteriorly at the pontomedullary junction just above pyramid, ascending from there through the prepontine cistern toward the clivus. Cochlear nerve nuclei are found on the lateral surface of the inferior cerebellar peduncle (restiform body).](48d8362b-1a93-40c1-930d-19e08cd22cdb)
*Abducens (CNVI) nerves exit the brainstem anteriorly at the pontomedullary junction just above pyramid, ascending from there through the prepontine cistern toward the clivus. Cochlear nerve nuclei are found on the lateral surface of the inferior cerebellar peduncle (restiform body).*
![CNVII and CNVIII exit the brainstem laterally at the pontomedullary junction to enter the cerebellopontine angle cistern. CNVII lies anterior to CNVIII in the cerebellopontine angle cistern. Notice CNVI piercing dura on the patient's left to enter the Dorello canal, an interdural channel passing along the dorsal surface of the clivus within the basilar venous plexus toward the CS.](2cdbd346-7902-4285-8303-2d4844ca5f6d)
*CNVII and CNVIII exit the brainstem laterally at the pontomedullary junction to enter the cerebellopontine angle cistern. CNVII lies anterior to CNVIII in the cerebellopontine angle cistern. Notice CNVI piercing dura on the patient's left to enter the Dorello canal, an interdural channel passing along the dorsal surface of the clivus within the basilar venous plexus toward the CS.*
![Meckel cave is formed by a dural reflection, lined with arachnoid and containing CSF. The gasserian ganglion (trigeminal ganglion) is semilunar in shape and lies anteroinferiorly in the Meckel cave.](93517950-97de-42d2-a31a-13fa43877430)
*Meckel cave is formed by a dural reflection, lined with arachnoid and containing CSF. The gasserian ganglion (trigeminal ganglion) is semilunar in shape and lies anteroinferiorly in the Meckel cave.*
![CNV exits the lateral pons at a point referred to as the root entry zone. Preganglionic segment courses anteriorly through the prepontine cistern and passes over the petrous apex to enter the Meckel cave via the porus trigeminus (entrance to Meckel cave).](36e27879-bfd4-40e2-ab28-c9421c7a9ab4)
*CNV exits the lateral pons at a point referred to as the root entry zone. Preganglionic segment courses anteriorly through the prepontine cistern and passes over the petrous apex to enter the Meckel cave via the porus trigeminus (entrance to Meckel cave).*
![In this image, the oculomotor nerve (CNIII) can be seen surrounded by high-signal CSF as it enters the roof of the CS. This area is referred to as the oculomotor cistern. CNIII travels anterolaterally, becoming incorporated into the lateral wall of the CS near the anterior clinoid process.](394e920d-e37b-4678-b099-4c27c93b2903)
*In this image, the oculomotor nerve (CNIII) can be seen surrounded by high-signal CSF as it enters the roof of the CS. This area is referred to as the oculomotor cistern. CNIII travels anterolaterally, becoming incorporated into the lateral wall of the CS near the anterior clinoid process.*
![At the level of the upper pons, important vascular relationships of CNIII passing between the PCA and SCA are visible. Notice CNIII coursing anteriorly within the suprasellar cistern adjacent to the posterior communicating artery. An aneurysm of the posterior communicating artery will result in compression of CNIII. More laterally in the perimesencephalic cistern, CNIV (trochlear nerve) also passes between PCA and SCA.](cb3af2fc-bc77-4bf1-8867-56464dda1f4b)
*At the level of the upper pons, important vascular relationships of CNIII passing between the PCA and SCA are visible. Notice CNIII coursing anteriorly within the suprasellar cistern adjacent to the posterior communicating artery. An aneurysm of the posterior communicating artery will result in compression of CNIII. More laterally in the perimesencephalic cistern, CNIV (trochlear nerve) also passes between PCA and SCA.*
![Anteriorly, note the optic nerves (CNII) form the optic chiasm in the suprasellar cistern. Fibers originating from the nasal halves of the retina cross within the optic chiasm. CNIII courses anteriorly within the suprasellar cistern toward the CS.](3734e1f2-326a-441f-8ff2-e2e4beead640)
*Anteriorly, note the optic nerves (CNII) form the optic chiasm in the suprasellar cistern. Fibers originating from the nasal halves of the retina cross within the optic chiasm. CNIII courses anteriorly within the suprasellar cistern toward the CS.*
![CNIII is seen on the patient's left, exiting the brainstem along the medial aspect of the cerebral peduncle, where it enters the interpeduncular cistern. The trochlear nerve (CNIV) decussates in the superior medullary velum, then exits along the dorsal surface of the midbrain below the inferior colliculus to enter the quadrigeminal plate cistern. From there, CNIV courses around the brainstem below the tentorium cerebelli in the ambient cistern passing between the PCA and SCA.](afa77221-557a-4ba7-bced-bfe992037851)
*CNIII is seen on the patient's left, exiting the brainstem along the medial aspect of the cerebral peduncle, where it enters the interpeduncular cistern. The trochlear nerve (CNIV) decussates in the superior medullary velum, then exits along the dorsal surface of the midbrain below the inferior colliculus to enter the quadrigeminal plate cistern. From there, CNIV courses around the brainstem below the tentorium cerebelli in the ambient cistern passing between the PCA and SCA.*
![Optic tracts connect the lateral geniculate body to the optic chiasm. Only a portion of the optic tracts are visible here.](e8fd39b2-baab-4655-b1c8-d02a2e8fcb42)
*Optic tracts connect the lateral geniculate body to the optic chiasm. Only a portion of the optic tracts are visible here.*
### Coronal T2 MR
![First of 6 coronal T2 MR images of the brainstem, cisterns, and cranial nerves presented from posterior to anterior is shown. Preganglionic segment of the trigeminal nerve is seen arising from the lateral pons. Also seen are the facial and vestibulocochlear nerves traversing the cerebellopontine angle cistern into the internal auditory canal.](6adcb52d-9061-410f-92a1-69e11cd819f1)
*First of 6 coronal T2 MR images of the brainstem, cisterns, and cranial nerves presented from posterior to anterior is shown. Preganglionic segment of the trigeminal nerve is seen arising from the lateral pons. Also seen are the facial and vestibulocochlear nerves traversing the cerebellopontine angle cistern into the internal auditory canal.*
![Oculomotor nerves are seen emerging from the medial aspect of the cerebral peduncle into the interpeduncular cistern. Basal cistern cranial nerves are not visible. The abrupt transition between the pons and the medulla is termed the pontomedullary junction.](70dd799b-82c4-49e5-9a36-f78e7e0a4822)
*Oculomotor nerves are seen emerging from the medial aspect of the cerebral peduncle into the interpeduncular cistern. Basal cistern cranial nerves are not visible. The abrupt transition between the pons and the medulla is termed the pontomedullary junction.*
![In this image, notice the oculomotor nerves passing between the PCA above and the SCA below. The distal preganglionic segment of CNV is poised to enter the porus trigeminus on its way into the Meckel cave.](8dfa1631-8813-4250-b9f2-67c077d6db0e)
*In this image, notice the oculomotor nerves passing between the PCA above and the SCA below. The distal preganglionic segment of CNV is poised to enter the porus trigeminus on its way into the Meckel cave.*
![This image shows the oculomotor nerve between the posterior communicating artery above and the SCA below. The trigeminal nerve is visible entering the porus trigeminus of the Meckel cave.](bcc900d3-7995-483c-a2df-45b32566fd92)
*This image shows the oculomotor nerve between the posterior communicating artery above and the SCA below. The trigeminal nerve is visible entering the porus trigeminus of the Meckel cave.*
![Here, the optic tracts are seen converging toward the optic chiasm. Note a large left anterior choroidal artery coursing posterolaterally within the suprasellar cistern. Preganglionic fibers of the trigeminal nerve are seen within the Meckel cave. The Meckel cave is formed by a reflection of dura, which is lined with arachnoid, contains CSF, and communicates freely with prepontine cistern.](546f13c1-f9bc-41f8-935e-b2fa0a94a74c)
*Here, the optic tracts are seen converging toward the optic chiasm. Note a large left anterior choroidal artery coursing posterolaterally within the suprasellar cistern. Preganglionic fibers of the trigeminal nerve are seen within the Meckel cave. The Meckel cave is formed by a reflection of dura, which is lined with arachnoid, contains CSF, and communicates freely with prepontine cistern.*
![In this most anterior coronal T2 image, the pituitary is seen below the optic chiasm. Notice the oculomotor nerve is entering the CS in the oculomotor cistern. The high-signal ring around CNIII is CSF.](1538a4b8-0cc8-4138-9024-6705bf6526be)
*In this most anterior coronal T2 image, the pituitary is seen below the optic chiasm. Notice the oculomotor nerve is entering the CS in the oculomotor cistern. The high-signal ring around CNIII is CSF.*
docs_md/articles/external-nose_8a7dc886-ee95-48cd-96e3-af45978db516.md
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---
title: "External Nose"
docid: "8a7dc886-ee95-48cd-96e3-af45978db516"
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---
## TERMINOLOGY
- ### Abbreviations
- Frontal process of maxilla (FPM)
- Anterior lacrimal crest (ALC)
- Posterior lacrimal crest (PLC)
- Internal nasal valve (INV)
- Nasal vestibular body (NVB)
- External nasal valve (ENV)
- ### Definitions
- **Glabella**: Smooth area between eyebrows, above nose
- **Nasion**: Most anterior aspect of frontonasal suture, situated just below glabella
- Midpoint of frontonasal suture intersection with upper end of median internasal suture (joining nasal bones)
- **Sellion**: Soft tissue equivalent of nasion
- Deepest point of nasofrontal angle at intersection of forehead slope & upper aspect of bridge of nose
- **Radix (root of nose)**: Origin of nose from glabella, extends equal distance superiorly & inferiorly centered at nasion
- Extends inferiorly from nasion to level of horizontal line drawn through lateral canthi
- Height of radix at nasion ideally between 9-14 mm as measured from anterior corneal plane
- **Rhinion**: Point at lower end of median internasal suture where nasal bones join with nasal septal cartilage
## IMAGING ANATOMY
- ### Overview
- **Dorsum of nose (nasal ridge)**: Outer surface between root & tip of nose
- **Ala (wing) of nose**: Lower lateral surface of external nose, kept in shape by alar cartilage & dense connective tissue; flare out around nostril
- **Nasal cavity**: Divided into 2 cavities by nasal septum, opens outside through external **nostril**
- **Nasal vestibule**: Most anterior aspect of nasal cavity lined with skin, hair follicles, & sebaceous glands, & surrounded by cartilages
- **Limen nasi (mucocutaneous junction)**: Mucous ridge separating skin-lined vestibule from respiratory epithelium-lined larger nasal cavity proper; contains dense microvasculature
- **Pyriform aperture of nose**: Pear-shaped anterior aperture at limen nasi level; anterior bony margin of nasal skeleton
- Superior margin: Nasal bone lower margin
- Inferolateral margin: Maxillary bone thin, sharp margins separating anterior from nasal surfaces of maxilla
- Curve medially joining premaxilla to form **anterior nasal spine of maxilla**
- **INV**: Narrowest portion of nasal cavity located ~ 1.3 cm from nares
- Area bordered inferiorly by head of inferior turbinate, medially by dorsal nasal septum, & laterally by caudal portion of upper lateral cartilage
- Static INV obstruction: Structural, lesion-like, enlarged turbinate or high nasal septal deviation
- Dynamic INV obstruction: Collapse of upper lateral cartilage/lateral nasal wall on inspiration due to weakness in their integrity
- **NVB**: Small mound of dynamic soft tissue in lateral aspect of INV, situated anteroinferior to head of inferior turbinate
- May contribute to nasal obstruction in some patients
- **ENV**: Area in nasal vestibule bordered by alar rim & columella, including medial crus, nasal spine, & soft tissues covering nostril sill
- Static ENV obstruction: Vestibular stenosis
- Dynamic ENV obstruction: Collapse of floppy, weak alar rim on inspiration
- ### Internal Contents
- **Nasal cartilages**: Septal, lateral, major (greater) alar, minor (lesser) alar, & vomeronasal
- **Septal** cartilage: In midline, from nasal bones anteroinferior meeting point (rhinion) anteriorly to bony nasal septum posteriorly; pass along nasal cavity floor
- Attached by loose ligaments laterally to bony margin of nasal pyriform aperture
- **Lateral** cartilage: Anterior margin thicker, attaches with & continues laterally from septal cartilage
- a.k.a.**upper****lateral**cartilage
- Superior margin attaches to nasal bone & FPM; inferior margin to greater alar cartilage by fibrous tissue
- **Major (greater) alar** cartilage: Thin, U-shaped cartilage plate attached to lateral cartilage superiorly & also anteroinferior aspect of septal cartilage
- a.k.a.**l****ower lateral**cartilage
- Bends along walls of vestibule: Medial & lateral crura
- Bilateral medial crura attaches to septal cartilage: Forms fleshy medial crural footpads in front of nostrils
- Medial crura meet in midline below end of septum to form columella & lobule
- **Columella**: Bridge of tissue at undersurface of nasal septum separating nostrils
- **Lobule**: **Tip of nose** & **nostrils**at its base
- **Alar domes**: Tip-defining points of nose at peaks of medial crural folds separated by notch
- Tip rhinoplasty or tip plasty: Shaping tip of nose by mainly reshaping greater alar cartilage
- Cartilage bends superolaterally around nostrils, forming lateral crura
- **Nasal scroll**: Formed by lateral & major cartilage edge interlocking by one scrolling upward & other inward
- Prevents internal nasal lumen collapse from airflow pressure during breathing
- **Minor (lesser or accessory) alar**cartilage: 3 or 4 cartilages within connective tissue membrane attaching lateral & major (greater) alar cartilages to FPM
- **Vomeronasal** (Jacobson) cartilage: Narrow cartilage strip in inferior nasal septum between septal cartilage & vomer of bony septum
- Lies below rudimentary vomeronasal (Jacobson) organ (VNO), which is accessory olfactory organ with blind sac & duct opening anteriorly
- VNO contains esthesiocytes (specialized olfactory sensory cells)
- VNO esthesiocytes may have role in afferent neurons of pheromone reception & in sexual gonadotropin-releasing hormone production
- VNO may be ectopic esthesioneuroblastoma origin site (usually originate in upper nasal cavity)
- **Areas with no cartilage support**: Small areas around septum, lateral cartilage, top of nostril, & in nasal ala
- Irregular notches on lower ends of nasal bones on either side of rhinion due to developmental variations at osteocartilaginous junction may mimic fractures
- **Bones****:** **Nasal bone**, **FPM,****lacrimal bone, &** **nasal septum**
- Common mistake: Misnaming FPM as nasal bone
- **Nasal septum**: Anterior septal cartilage & posterior bone
- Bony septum: **Perpendicular plate of ethmoid** posterosuperiorly, **vomer** posteroinferiorly, & **maxillary crest** at undersurface
- Maxillary crest: Narrow bone strip projecting superiorly from maxilla anteriorly & palatine bone posteriorly along anteroposterior length of septum
- Articulates above with septal cartilage anteriorly & vomer posteriorly
- Columella: Forms external undersurface of nasal septum, composed of cartilage & soft tissue
- **Philtrum**: Vertical groove in midline of upper lip, just below columella
- Nasal septum divides triangular nasal cavity in 2
- **Sutures**
- **Internasal** suture: Between nasal bones of both sides
- Top point meets nasion & bottom point forms rhinion
- **Nasomaxillary** suture: Between nasal bone & FPM
- **Frontonasal** suture: Between nasal bones of both sides & frontal bone superiorly
- Nasion forms its most anterior aspect where it meets internasal suture
- **Frontomaxillary** suture: Between FPM & nasal process of frontal bone superiorly
- Continuous medially with frontonasal suture
- **Lacrimal fossa**: Formed by thick**ALC** of FPM & thin **PLC** of lacrimal bone
- **Lacrimal sac**: Lies within lacrimal fossa, invested by superficial & deep parts of orbicularis oculi muscle
- Lacrimal sac below **medial canthal tendon (MCT)**not covered by muscle, potential site of weakness for intraorbital spread of infection
- **Medial orbital septum** & check ligament of medial rectus muscle attach just posterior to PLC of lacrimal bone
- Therefore,**lacrimal fossa & lacrimal sac**considered **preseptal**structures
- Preseptal location important in treatment plan of lacrimal sac infection, mainly antibiotics
- Orbital septum attaches to orbital margin at "arcus marginale," thickening where periorbita joins periosteum
- **MCT injury &** status of central fragment of fractured bone extremely important in **nasoorbitoethmoid (NOE) fracture**management
- MCT injury can lead to medial telecanthal deformities, such as shortened palpebra, obtuse angled medial canthi with infraplacement, increased intercanthal distance, & absent nasoorbital valley
- MCT: 3 limbs attached to bones (fractures of these bones important to assess in every trauma CT scan)
- Anterior (strongest limb) attaches to ALC of FPM & continues into periosteum of nasal bone
- Posterior limb attaches to PLC of lacrimal bone (difficult to fix injury as PLC & lacrimal bone are delicate)
- Superior limb attaches to medial orbital rim few mm above anterior limb
- ### Muscles Inserting at Nose
- Nasal**elevators**: Anomalous nasi & 2 extrinsic muscles, namely, procerus (inserting at orbit) & levator labii superioris alaeque nasi (LLSAN), (inserting at upper lip with medial slip inserting into greater alar cartilage)
- Nasal**depressors**: Alar nasalis & depressor septi nasi
- Nasal**compressors**: Transverse nasalis & compressor narium minor
- Nasal**dilators**: Dilator naris anterior (DNA), dilator naris vestibularis (DNV), & contribution from alar nasalis & LLSAN
- **Procerus**: Origin on lower end of nasal bone & upper part of lateral nasal cartilage
- Inserts on forehead skin medial to eye & interdigitates with frontalis muscle
- Displace medial angle of eyebrow down & elevates nose
- **LLSAN**: Origin on FPM & inserts in 2 places: One at greater alar cartilage & skin of nose, other at muscles of upper lip
- Elevates nose & dilates nares, displaces upper lip superomedially
- **Anomalous nasi**: Origin on FPM & inserts into nasal bone, lateral nasal cartilage, & procerus & transverse nasalis; is nasal elevator
- **Transverse nasalis**: Nasalis muscle has 2 parts, namely, transverse nasalis & alar nasalis
- Origin of transverse nasalis on canine eminence of maxilla superolateral to incisive fossa
- Inserts, expanding into thin aponeurosis continuous on bridge of nose with that of opposite side transverse nasalis & with aponeurosis of procerus
- Main nasal compressor; hyperactivity can cause radial lines along dorsum of nose as far down to lower border of greater alar cartilage, called "bunny lines"
- **Alar nasalis**: Origin on maxilla just medial to transverse nasalis above lateral incisor tooth, located anterior to transverse nasalis
- Ascends anterolaterally to insert on alar-facial crease & adjacent deep surface of external skin of alar lobule
- Is nasal depressor & also helps to dilate nares (hence, sometimes called dilator naris posterior)
- **Depressor septi nasi**: Origin in incisive fossa of maxilla located further medial to origin of alar nasalis
- Inserts on base & lateral surface of medial crus of greater alar cartilage; is nasal depressor
- Medially, attaches to dermocartilagenous ligament, which is sandwiched by medial crus of greater alar cartilage
- **DNA**: Origin on frontal surface of lateral 1/2 of lateral crus of greater alar cartilage & adjacent lesser alar cartilage
- Inserts on skin of nose superior to alar groove (supraalar crease); is nasal dilator
- **DNV**: Origin on external skin of alar lobule, radiates along dome of nasal vestibule
- Inserts on vestibular skin of alar lobule; is dilator of nasal vestibule
- **Compressor narium minor**: Origin on anterior part of greater alar cartilage
- Inserts into skin near margin of nostril; is nasal compressor
5e416fb0-dd52-4381-834b-6797f8da48a9
## Images
### 3D Reconstructions of External Nose
![3D soft tissue CT shows the important surface markings of the external nose.](images/app.statdx.com_image_thumbnail_696886db-b6dd-46be-a383-886c9d91ca6c_annotated_false_size_900_quality_90_aee788a117d5cbcfd5dd8d5e0632066f41a05984.jpg)
*3D soft tissue CT shows the important surface markings of the external nose.*
![3D soft tissue CT shows the important surface markings of the external nose.](images/app.statdx.com_image_thumbnail_696886db-b6dd-46be-a383-886c9d91ca6c_size_174_quality_85_f3337420c66ee4f0f91548885410d1986beefea2.jpg)
*3D soft tissue CT shows the important surface markings of the external nose.*
![Anterior 3D bone CT of external nose skeleton shows the paired nasal bones with an internasal suture between them, &amp; the frontal process of maxilla (FPM) lateral to it separated by a nasomaxillary suture. The nasion is the most anterior aspect of frontonasal suture, &amp; the rhinion is the point at the lower end of the median internasal suture where nasal bones join with nasal septal cartilage. Bony nasal septum consists of the perpendicular plate of ethmoid posterosuperiorly, vomer posteroinferiorly, &amp; narrow bony strip, known as maxillary crest, at its undersurface.](images/app.statdx.com_image_thumbnail_b5e38281-a4ca-4b13-97d9-479036d86944_annotated_false_size_900_quality_90_266ba2310b61f39179381d74c13374f5ec19e49a.jpg)
*Anterior 3D bone CT of external nose skeleton shows the paired nasal bones with an internasal suture between them, &amp; the frontal process of maxilla (FPM) lateral to it separated by a nasomaxillary suture. The nasion is the most anterior aspect of frontonasal suture, &amp; the rhinion is the point at the lower end of the median internasal suture where nasal bones join with nasal septal cartilage. Bony nasal septum consists of the perpendicular plate of ethmoid posterosuperiorly, vomer posteroinferiorly, &amp; narrow bony strip, known as maxillary crest, at its undersurface.*
![Anterior oblique 3D bone CT of external nose skeleton shows the nasal bone &amp; FPM of the left side separated by a nasomaxillary suture. The more posteriorly situated lacrimal bone, which forms posterior lacrimal crest (PLC) of lacrimal fossa in the medial orbit, is also shown. Note anterior nasal spine of maxilla situated inferiorly. Lamina papyracea forms medial wall of orbit/lateral wall of ethmoid air cells &amp; is seen posterior to lacrimal bone. Frontonasal suture is continuous laterally with frontomaxillary suture.](images/app.statdx.com_image_thumbnail_a79b23d6-d3b5-4b50-b103-cef342389556_annotated_false_size_900_quality_90_3762d12b6aedf0edfa2c5dfe82366bd63bad81ca.jpg)
*Anterior oblique 3D bone CT of external nose skeleton shows the nasal bone &amp; FPM of the left side separated by a nasomaxillary suture. The more posteriorly situated lacrimal bone, which forms posterior lacrimal crest (PLC) of lacrimal fossa in the medial orbit, is also shown. Note anterior nasal spine of maxilla situated inferiorly. Lamina papyracea forms medial wall of orbit/lateral wall of ethmoid air cells &amp; is seen posterior to lacrimal bone. Frontonasal suture is continuous laterally with frontomaxillary suture.*
### Axial CT Scan of Bones of External Nose
![Axial bone CT of the external nose at the orbital level shows the 3 bones forming its skeleton, namely, the nasal bone, FPM, &amp; lacrimal bone. It is a common mistake in radiology reports to call an FPM fracture a nasal bone fracture. The lacrimal fossa is formed by the thick anterior lacrimal crest of the FPM &amp; thin PLC of the lacrimal bone. The lacrimal sac lies within the lacrimal fossa &amp; is invested by superficial &amp; deep parts of the orbicularis oculi muscle. Lacrimal sac below the medial canthal tendon (MCT) is not covered by muscle &amp; is a potential weakness site for intraorbital infection spread. Look for MCT/bony attachment injury in nasoorbitoethmoid fractures. Medial orbital septum &amp; check ligament of medial rectus muscle attach just posterior to PLC of lacrimal bone, hence, the lacrimal fossa &amp; lacrimal sac are preseptal structures.](images/app.statdx.com_image_thumbnail_5c50a1e3-9f78-414a-8300-7e36e67a424c_annotated_false_size_900_quality_90_a4cb1bcfd62c938c82d1bd17e671cc74bbd680ee.jpg)
*Axial bone CT of the external nose at the orbital level shows the 3 bones forming its skeleton, namely, the nasal bone, FPM, &amp; lacrimal bone. It is a common mistake in radiology reports to call an FPM fracture a nasal bone fracture. The lacrimal fossa is formed by the thick anterior lacrimal crest of the FPM &amp; thin PLC of the lacrimal bone. The lacrimal sac lies within the lacrimal fossa &amp; is invested by superficial &amp; deep parts of the orbicularis oculi muscle. Lacrimal sac below the medial canthal tendon (MCT) is not covered by muscle &amp; is a potential weakness site for intraorbital infection spread. Look for MCT/bony attachment injury in nasoorbitoethmoid fractures. Medial orbital septum &amp; check ligament of medial rectus muscle attach just posterior to PLC of lacrimal bone, hence, the lacrimal fossa &amp; lacrimal sac are preseptal structures.*
![Axial bone CT further inferiorly shows nasomaxillary suture separating the nasal bone from the FPM. Note the nasolacrimal duct, which continues inferiorly from the lacrimal sac, &amp; opens in the inferior meatus of the nose (not shown).](images/app.statdx.com_image_thumbnail_d6fb5661-3c78-4b92-ae5a-6ab191597c40_annotated_false_size_900_quality_90_89ec9f789f0d43298d2be42f04941dba0704ad0e.jpg)
*Axial bone CT further inferiorly shows nasomaxillary suture separating the nasal bone from the FPM. Note the nasolacrimal duct, which continues inferiorly from the lacrimal sac, &amp; opens in the inferior meatus of the nose (not shown).*
![Axial bone CT through the lower aspect of the nose shows the anterior nasal spine of maxilla.](5b44f239-5caa-4850-b68b-a91fce15842c)
*Axial bone CT through the lower aspect of the nose shows the anterior nasal spine of maxilla.*
### Cartilages & Bones of External Nose
![Anterior 3D bone CT (above) and axial bone CT (below) show irregular notches at the lower ends of the nasal bones due to developmental variations at the osteocartilaginous junction, which should not be mistaken for fractures.](1699d101-5b58-43ab-8ea9-be6ee519ff0b)
*Anterior 3D bone CT (above) and axial bone CT (below) show irregular notches at the lower ends of the nasal bones due to developmental variations at the osteocartilaginous junction, which should not be mistaken for fractures.*
![Coronal bone CT images from anterior to posterior show the anteriorly located nasal bone &amp; anteroinferior aspect of the FPM separated by the nasomaxillary suture in the most anterior image. Also note the anterior nasal spine of the maxilla projecting anteriorly. The slightly posterior CT through the frontonasal suture level shows less portions of nasal bones &amp; more of FPM. Further posterior CT behind the level of nasal bones shows the FPM &amp; frontomaxillary suture. Note the nasal septum in midline in all the images, which is predominantly cartilaginous anteriorly &amp; bony posteriorly.](ca59d94f-c767-4bbc-80c8-d09709153299)
*Coronal bone CT images from anterior to posterior show the anteriorly located nasal bone &amp; anteroinferior aspect of the FPM separated by the nasomaxillary suture in the most anterior image. Also note the anterior nasal spine of the maxilla projecting anteriorly. The slightly posterior CT through the frontonasal suture level shows less portions of nasal bones &amp; more of FPM. Further posterior CT behind the level of nasal bones shows the FPM &amp; frontomaxillary suture. Note the nasal septum in midline in all the images, which is predominantly cartilaginous anteriorly &amp; bony posteriorly.*
![3D CT scan windowed to show cartilage and bone: Septal cartilage extends from rhinion (lower end of median internasal suture) anteriorly to bony nasal septum posteriorly. Three or 4 minor (lesser/accessory) alar cartilages lie within the connective tissue membrane attaching upper lateral and major/greater alar (lower lateral) cartilages to FPM.](9e7edab7-b252-4b5e-8c07-502c34542f39)
*3D CT scan windowed to show cartilage and bone: Septal cartilage extends from rhinion (lower end of median internasal suture) anteriorly to bony nasal septum posteriorly. Three or 4 minor (lesser/accessory) alar cartilages lie within the connective tissue membrane attaching upper lateral and major/greater alar (lower lateral) cartilages to FPM.*
### Muscles Attaching Around External Nose
![Frontal graphic shows facial muscles attaching into external nose (purple). Note that 2 extrinsic muscles, namely, procerus (blue, attaching around eye) &amp; levator labii superioris alaeque nasi [(LLSAN), yellow, attaching at upper lip] are also nasal elevators.](bd365583-0305-455d-b41e-49592d8a8640)
*Frontal graphic shows facial muscles attaching into external nose (purple). Note that 2 extrinsic muscles, namely, procerus (blue, attaching around eye) &amp; levator labii superioris alaeque nasi [(LLSAN), yellow, attaching at upper lip] are also nasal elevators.*
![Coronal 3-mm T2 MRs from anterior to posterior are shown. First MR shows tiny nasal muscles, which do not have bony origins. Second MR shows depressor septi nasi originating in maxillary incisive fossa; just lateral to this lies alar nasalis originating above maxillary lateral incisor, &amp; further laterally is transverse nasalis (TN) originating from maxillary canine eminence. As their name implies, depressor septi nasi inserts near nasal septum into medial crus of greater alar cartilage, alar nasalis lies anterior to TN &amp; inserts into nasal alar lobule skin &amp; alar-facial crease, &amp; TN continues superiorly across bridge of nose. Third image shows procerus inserting around eye.](5b74a491-a77f-4731-b47a-b69858da623e)
*Coronal 3-mm T2 MRs from anterior to posterior are shown. First MR shows tiny nasal muscles, which do not have bony origins. Second MR shows depressor septi nasi originating in maxillary incisive fossa; just lateral to this lies alar nasalis originating above maxillary lateral incisor, &amp; further laterally is transverse nasalis (TN) originating from maxillary canine eminence. As their name implies, depressor septi nasi inserts near nasal septum into medial crus of greater alar cartilage, alar nasalis lies anterior to TN &amp; inserts into nasal alar lobule skin &amp; alar-facial crease, &amp; TN continues superiorly across bridge of nose. Third image shows procerus inserting around eye.*
![Axial T1 MR at level of eye lens (top) shows origin of procerus muscle on the nasal bone &amp; anomalous nasi on FPM. Axial T1 MR just below inferior orbital margin at upper maxillary sinus level (bottom) shows levator labii superioris alaeque nasi origin on FPM.](6019e041-1751-450d-a72e-4172032eaf0f)
*Axial T1 MR at level of eye lens (top) shows origin of procerus muscle on the nasal bone &amp; anomalous nasi on FPM. Axial T1 MR just below inferior orbital margin at upper maxillary sinus level (bottom) shows levator labii superioris alaeque nasi origin on FPM.*
docs_md/articles/facial-muscles-and-superficial-musculoaponeurotic-system_80a3629d-d41e-4efd-9dac-4f19bbdea9db.md
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title: "Facial Muscles and Superficial Musculoaponeurotic System"
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---
## TERMINOLOGY
- ### Abbreviations
- Superficial musculoaponeurotic system (SMAS)
- ### Definitions
- Mimetic muscles/mimic muscles/muscles of facial mimicry: Primary function is facial expression
- Muscles insert directly into dermis via SMAS facilitating facial expression (in rest of body, investing layer of fascia separates muscle from subcutaneous tissue)
- SMAS: Continuous organized fibrous network connecting facial muscles to dermis
- Modiolus: Dense fibromuscular structure formed at corner of mouth lateral border by attached muscles convergence
## IMAGING ANATOMY
- ### Overview
- Muscles of facial mimicry have their origin on bone but insert directly into dermis (through SMAS)
- Exceptions are inconsistently found in risorius & malaris muscles with both origin & insertion in soft tissue
- Other exceptions are tiny nasal muscles, namely, compressor narium minor, dilator naris anterior (DNA) (both have origin from nasal cartilages & insert into skin)
- Mimetic muscles act as sphincters & dilators of facial orifices & elevators & depressors of facial structures
- Adjacent muscles closely intertwined due to their common origin from mesoderm of 2nd branchial arch; large muscular sheets later differentiate into individual muscles
- Groups of facial muscles share common insertion sites; therefore, identification is often easiest by tracing them back from their insertion to less crowded origins
- 6 groups for purpose of easy identification, namely, muscles inserting at: (1) Scalp, (2) orbit, (3) nose, (4) upper lip, (5) modiolus/angle of mouth, & (6) lower lip
- ### Anatomy Relationships
- Layers of face, from superficial to deep
- **(1) Skin**
- **(2) Subcutaneous fat**
- Extensive in cheek region (**malar fat pad**); less in eyelid, lips, & nose
- Malar fat pad slides downward & inward over SMAS with aging, deepening nasolabial crease
- Malar fat pad firmly fixed to dermis & also to thicker superior part of SMAS but loosely attached to thinner inferior SMAS
- Zygomatic ligament: Osteocutaneous ligament on zygoma lateral to zygomaticus minor (ZMi) muscle origin, anchors malar fat to deeper tissue layers
- Fat pad beneath orbicularis oculi (OOc) muscle called **suborbicularis oculi fat pad**
- **(3) SMAS (superficial fascia)**
- Connects facial muscles to skin dermis
- SMAS continuous above with **temporoparietal fascia** (TpF) as it passes over zygomatic arch
- **TpF** a.k.a. superficial **temporal fascia**or **epicranial aponeurosis**
- TpF, in turn, continuous with galea aponeurotica in scalp superiorly, frontalis muscle anteriorly, & occipitalis muscle posteriorly
- TpF usually fibrous, sometimes contains vestigial muscles, namely, **temporoparietal muscle** & **superior auricular muscle**
- SMAS extremely thin beyond anterior border of masseter as it enters cheek area, barely traceable by position of split peripheral part of platysma
- SMAS blends with platysma inferiorly & begins fading medially as it reaches lateral nasal margin
- Lower 1/2 of SMAS is extremely thin & somewhat discontinuous with no mechanical bearing capacity
- SMAS invests in & extends into external aspects of facial muscles, mainly frontalis, OOc, ZMi, zygomaticus major (Zmj), risorius, orbicularis oris (OOr), & platysma
- SMAS composed of 3D scaffold of collagen & elastic fibers with interspersed fat cells
- 2 distinct histologic subtypes of SMAS described
- **Type 1**: SMAS lateral to nasolabial fold (NLF)
- Meshwork of fibrous septa that envelop large lobules of fat cells & allow for connections with both facial muscles as well as periosteum
- More susceptible to aging process than type 2
- **Type 2**: SMAS medial to NLF, mainly in lips
- Meshwork of intermingled collagen, elastic & muscle fibers reaching up into dermis
- Much firmer connection to skin than type 1, fat cells lie dispersed unlike distinct fat lobules in type 1
- Transition between types 1 & 2 SMAS at NLF: Challenge for facial rejuvenation surgeries
- CT: Hyperdense line between superficial & deep fibroadipose tissue; MR: T1-/T2-hypointense line
- **(4) Superficial facial muscles ("mimic****muscles"**): 6 groups
- **(5) Parotideomasseteric fascia (deep fascia)**: Investing fascia enveloping parotid gland, duct, & masseter muscle
- Also envelop facial nerve branches in parotid gland & part of buccal fat pad
- Note: **Buccal fat pad** lies just outside corners of mouth; deeper layer than **malar fat pad** lying in front part of cheek
- Continues to superficial layer of deep cervical fascia inferiorly & superiorly to temporalis fascia (a.k.a. deep temporal fascia)
- Temporalis fascia, in turn, covers temporalis muscle, splits inferiorly attaching around zygomatic arch, & attaches superiorly to pericranium at and above superior temporal line on skull
- **(6) Retaining ligaments**: Connects overlying structures to underlying periosteum of facial bones
- **Facial nerve branches in parotid gland** lie **deep** underneath parotideomasseteric fascia (deep fascia in cheek deep to SMAS), making **sub-SMAS dissection safe during facelift surgery**at this level
- Facial nerve branches eventually traverse deep fascia in their anteromedial superficial course to innervate muscles of SMAS, most of which receive innervation from their deep surfaces
- Facial nerve fibers become more superficial medially beyond facial artery & vein; important anatomy note to avoid injury during face lift surgery
- **Facial nerve (CNVII) branches course in face**
- **Zygomatic arch level**: In loose areolar tissue plane between TpF & zygomatic arch periosteum
- **1 cm above zygomatic arch**: In loose areolar plane between superficial TpF & deep temporalis fascia
- **2 cm above zygomatic arch**: Penetrates TpF to run along anterior branch of superficial temporal artery
- **Facial artery** curves upward over body of mandible at anteroinferior angle of masseter muscle → pass anterosuperiorly across cheek to ~ 8-23 mm lateral to labial commissure → ascends along side of nose to end at medial commissure of eye as **angular artery**
- Accompanied by **facial & angular veins**
- **Internal maxillary artery**, including its**infraorbital artery** branch lying in between levator labii superioris (LLS) & levator anguli oris (LAO) muscles, & **superficial temporal arter****y** also supplies face
- ### Internal Contents
- 6 groups of facial muscles based on insertion site
- ### I: Muscles Inserting at Scalp
- **Frontal belly of occipitofrontalis (frontalis muscle):**Origin from epicranial aponeurosis near coronal suture & insertion at skin of frontal region & galea aponeurotica
- Partially intertwined with muscle fibers of adjacent corrugator supercilii (CS), procerus, & OOc
- Furrows forehead, raises eyebrows, & widens eyes
- Can cause **horizontal hyperfunctional facial lines on forehead**; treatment with botulinum toxin injection
- ### II: Muscles Inserting at Orbit
- **OOc**: Origins: **Palpebral** part from medial palpebral ligament, a.k.a. medial canthal tendon, **orbital** part from medial orbital rim, & **lacrimal** part from lacrimal bone
- Palpebral part inserts on lateral palpebral raphe, orbital part inserts laterally to palpebral portion, & lacrimal part inserts at upper & lower eyelids
- Medially, muscle is deep to medial canthal tendon
- Palpebral part helps in light closure of eyelids
- Orbital part used for more forceful closure along with medial displacement of eyelids
- Compress eye globe & lacrimal sac to initiate flow of tears into nasolacrimal duct
- Hyperactivity of lateral OOc can produce radial lines stemming from lateral canthus ("**crow's feet**")
- **Malaris**muscle: Inconsistent lateral muscular band of OOc originating from TpF & terminates at either zygomatic arch or cheek region or angle of mouth
- Plays role in facial animation
- Inconsistent medial muscular bands may be present
- Preventing drooping of OOc
- Many muscular connections between OOc & ZMi
- May play role in facial expression
- CS: Origin on frontal bone at medial supraorbital margin & inserts into frontalis; deep to frontalis; 2 bellies
- Deep transverse belly & superficial oblique belly
- Deep to frontalis
- Depresses brow, pulls it medially, & **creates vertical skin creases as in frowning**
- **Depressor supercilii (DS)**: Origin in region of medial orbital rim on frontal process of maxilla (FPM) 2-5 mm below frontomaxillary suture; some fibers from lacrimal sac
- Inserts into dermis 14-15 mm superior to medial canthal tendon (medial palpebral ligament)
- DS interdigitates with adjacent OOc & CS
- Depresses medial aspect of brow during frowning
- **Procerus**: Origin on lower end of nasal bone & upper part of upper lateral nasal cartilage
- Inserts on forehead skin medial to eye & interdigitates with frontalis muscle
- Displaces medial angle of eyebrow inferiorly, which also causes **horizontal facial skin creases, frowning**
- Elevator of nose
- ### III: Muscles Inserting at Nose
- Nasal **elevators**: Anomalous nasi & 2 extrinsic muscles, namely, procerus (inserting at orbit) & LLS alaeque nasi (LLSAN) (inserting at upper lip with medial slip inserting into greater alar cartilage)
- Nasal **depressors**: Alar nasalis & depressor septi nasi
- Nasal **compressors**: Transverse nasalis & compressor narium minor
- Nasal **dilators**: DNA, dilator naris vestibularis (DNV), & contribution from alar nasalis & LLSAN
- **Anomalous nasi**: Origin on FPM & inserts into nasal bone, upper lateral nasal cartilage, procerus, & transverse nasalis; is nasal elevator
- **Transverse nasalis**: Nasalis muscle has 2 parts, namely, transverse nasalis & alar nasalis
- Origin of transverse nasalis on canine eminence of maxilla superolateral to incisive fossa
- Inserts, expanding into thin aponeurosis continuous on bridge of nose with that of opposite side transverse nasalis & with aponeurosis of procerus
- Main nasal compressor; hyperactivity can cause radial lines along dorsum of nose as far down to lower border of greater alar cartilage called "**bunny lines**"
- **Alar nasalis**: Origin on maxilla just medial to transverse nasalis above lateral incisor tooth, located anterior to transverse nasalis
- Ascends anterolaterally to insert on alar-facial crease & adjacent deep surface of external skin of alar lobule
- Is nasal depressor; also helps to dilate nares (hence, sometimes called **dilator naris posterior**)
- **Depressor septi nasi**: Origin in incisive fossa of maxilla located further medial to origin of alar nasalis
- Inserts on base & lateral surface of medial crus of greater alar cartilage; is nasal depressor
- Medially, attach to dermocartilagenous ligament, which gets sandwiched by medial crus of greater alar cartilage
- **DNA**: Origin on frontal surface of lateral 1/2 of lateral crus of greater alar cartilage & adjacent lesser alar cartilage
- Inserts on skin of nose superior to alar groove (supraalar crease); is nasal dilator
- **DNV**: Origin on external skin of alar lobule, radiates along dome of nasal vestibule
- Inserts on vestibular skin of alar lobule; dilator of nasal vestibule (nasal vestibule: Most anterior nasal cavity)
- **Compressor narium minor**: Origin on anterior part of greater alar cartilage
- Inserts into skin near margin of nostril; is nasal compressor
- ### IV: Muscles Inserting at Upper Lip
- **LLS**: Origin on inferior margin of orbit just above infraorbital foramen deep to OOc & inserts on upper lip; raises upper lip
- **LLSAN**: Origin on FPM & inserts in 2 places
- Insertion at greater alar cartilage & skin of nose: Elevates nose & dilates nares
- Insertion at muscles of upper lip: Displaces upper lip superomedially
- LLSAN & LLS can be injected with botulinum toxin to decrease **gingival show** or "**gummy smile**" whereby they are prevented from contracting, which, in turn, decreases superior displacement of upper lip
- **ZMi**: Origin on anterior aspect of zygomatic bone posterior to zygomaticomaxillary suture & inserts on upper lip
- Inserts to both upper lip & ala of nose in ~ 1/4 of cases
- Displaces upper lip superiorly, resulting in deepening of nasolabial furrow during expression of contempt
- LLS, LLSAN, & ZMi pass through OOr at upper lip insertion contributing to**NLF**
- ### V: Muscles Inserting at Modiolus/Angle of Mouth
- Tendinous tissue nodule in modiolus seen in 20%; facial artery passes 1 mm lateral to lateral border of modiolus
- **ZMj**: Origin on zygoma (behind ZMi origin) anterior to zygomaticotemporal suture & inserts at modiolus
- At modiolar insertion, deep to LAO
- If ZMj is bifid, then LAO passes between its 2 heads
- Main insertion of deep muscle band of ZMj **at anterior margin of buccinator**muscle & its fascia
- Key relationship in facial animation (even though buccinator not classified as muscle of facial mimicry)
- Raises angle of mouth superiorly & posteriorly & helps to smile or laugh
- **Bifid ZMj**can cause **cheek "dimple"** due to fascial strands inserting into dermis & causing dermal tethering effect
- **OOr**: Origin from other facial muscles converging to mouth; bony origin of upper portion on alveolar border of maxilla & lower portion on mandible lateral to mentalis; insert at angle of mouth
- Sphincter of mouth, which brings lips close to teeth & alveoli, brings lips together & protrudes lips forward
- Hyperactivity can result in radial lines around mouth, a.k.a. "**lipstick lines**" or "**smoker's lines**"; treated with botulinum toxin in combination with lip fillers
- **LAO**: Origin in canine fossa of maxilla well below infraorbital foramen & inserts at modiolus just superficial to ZMj insertion
- Displaces lip angle superiorly & results in deepening of nasolabial furrow
- In its superior aspect, LAO lies deep to LLS; **infraorbital vessels & nervous plexus** lie between them
- **Depressor anguli oris (DAO)**: Origin on oblique line of mandible lateral & inferior to depressor labii inferioris (DLI)
- Also interdigitates with platysma & inserts at corner of mouth as narrow fasciculus
- Depresses angle of mouth during grief & displaces angle medially on simultaneous contraction with LAO
- Some fibers may continue below mental tubercle joining contralateral DAO & creating **transversus menti** muscle
- **Risorius**: Inconsistent muscle, most fibers originating from SMAS (superficial fascia), some fibers from parotidomasseteric fascia (deep fascia); in some cases receives platysma fibers
- Inserts at modiolus in 3 distinct superficial, flush, & deep layers in relation to DAO
- Displaces skin of cheek posteriorly, stretches lower lip & displaces corner of mouth inferolaterally during grinning
- ### VI: Muscles Inserting at Lower Lip
- **DLI**: Origin on oblique line of mandible between mental foramen & symphysis (superomedial to DAO origin), also interdigitates with platysma
- Inserts on skin of lower lip & OOr
- Displaces lower lip inferiorly & slightly laterally
- **Mentalis**: Origin in incisive fossa of mandible & inserts on skin of chin; only elevator of lower lip
- Elevates & protrudes lower lip & can wrinkle chin; if deep, is treated with botulinum toxin
- **Platysma**: Origin on superficial pectoral & deltoid fascia & inserts on inferior body of mandible, skin, & hypodermis
- Depresses lower mandible & lower lip
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Most "mimic muscles" identified in thin-section CT & 3-mm T1 & T2 MR with accurate knowledge of anatomy
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Important landmarks for surgical procedures: Facial rejuvenation, rhytidectomy (face lift), cleft lip/palate repair
- Facial wrinkles occur perpendicular to muscle action there; important for injection treatment, such as botulinum toxin
- Atrophy of facial fat pads plays significant role in aging
- "**Marionette lines**" or "**melomental folds**": Long vertical lines laterally circumscribing chin, extending downward from oral commissures; appear with aging
- When ligaments, skin, & fat around mouth & chin sag
- Treated with injectable fillers & surgeries, such as face lift
- Imaging identification of denervation changes in facial muscles: Numerous etiologies, including neoplasms
- Involved in tumors, including lesions along SMAS & facial muscles & perineural spread along CNV & CNVII in relation to SMAS: Lymphoma, squamous cell carcinoma
- ### Major Contributor Muscles to Common Facial Expressions
- **Surprise**: Frontalis
- **Frowning**: CS, DS, & procerus
- **Anger**: DNA, DNV, depressor septi nasi
- **Contempt**: ZMi
- **Smiling & laughing**: ZMj
- **Grinning:** Risorius
- **Sadness**: LLS, LAO; grief: DAO
- **Doubt**: Mentalis
- **Whistling**: Buccinator, OOr
- **Horror, terror, & fright**: Platysma
70097b04-0ef5-4626-adaa-ed831981e9a7
## Images
### Facial Muscles: Graphic & 3D Bone CT Reformat of Skull
![Frontal graphic shows facial mimic muscles color-coded into 6 groups according to common insertion sites: The scalp is green, orbit is blue, nose is purple, upper lip is yellow, modiolus/angle of mouth is red, &amp; lower lip is magenta. Muscles inserting around the scalp, orbit, &amp; nose only are marked with line captions in this image.](images/app.statdx.com_image_thumbnail_6172bbf8-8c05-4fe5-814d-1c5e0e8de6c1_annotated_false_size_900_quality_90_cff66b7c30e8d50f7a9de446555fde8b95306441.jpg)
*Frontal graphic shows facial mimic muscles color-coded into 6 groups according to common insertion sites: The scalp is green, orbit is blue, nose is purple, upper lip is yellow, modiolus/angle of mouth is red, &amp; lower lip is magenta. Muscles inserting around the scalp, orbit, &amp; nose only are marked with line captions in this image.*
![Frontal graphic shows facial mimic muscles color-coded into 6 groups according to common insertion sites: The scalp is green, orbit is blue, nose is purple, upper lip is yellow, modiolus/angle of mouth is red, &amp; lower lip is magenta. Muscles inserting around the scalp, orbit, &amp; nose only are marked with line captions in this image.](images/app.statdx.com_image_thumbnail_6172bbf8-8c05-4fe5-814d-1c5e0e8de6c1_size_174_quality_85_3d3d4e71afd6cdf1d3c6e2a642cf871d3edf4713.jpg)
*Frontal graphic shows facial mimic muscles color-coded into 6 groups according to common insertion sites: The scalp is green, orbit is blue, nose is purple, upper lip is yellow, modiolus/angle of mouth is red, &amp; lower lip is magenta. Muscles inserting around the scalp, orbit, &amp; nose only are marked with line captions in this image.*
![The origin of facial muscles is painted on this 3D skull CT. Muscle groups follow color coding seen on the previous graphic according to their insertion sites. Muscles of facial mimicry have their origin on bone &amp; insert into the dermis through the superficial musculoaponeurotic system (SMAS). Exceptions are inconsistently found in the risorius &amp; malaris muscles, having both origin and insertion in soft tissue, &amp; also the tiny nasal muscles, namely, the compressor narium minor, dilator naris anterior (DNA) (both have origin from nasal cartilages and insert into skin), &amp; dilator naris vestibularis (DNV) (origin and insertion in skin). In this image, these muscle origins are painted with white outlines outside their respective internal color coding. The origin of muscles inserting around the orbit (blue) &amp; nose (purple) only are explained with line captions.](images/app.statdx.com_image_thumbnail_6a7814b1-dd54-4709-bba8-d37537816203_annotated_false_size_900_quality_90_8bcb80fdabef4a112d6f2431ccec068f0d1e59a9.jpg)
*The origin of facial muscles is painted on this 3D skull CT. Muscle groups follow color coding seen on the previous graphic according to their insertion sites. Muscles of facial mimicry have their origin on bone &amp; insert into the dermis through the superficial musculoaponeurotic system (SMAS). Exceptions are inconsistently found in the risorius &amp; malaris muscles, having both origin and insertion in soft tissue, &amp; also the tiny nasal muscles, namely, the compressor narium minor, dilator naris anterior (DNA) (both have origin from nasal cartilages and insert into skin), &amp; dilator naris vestibularis (DNV) (origin and insertion in skin). In this image, these muscle origins are painted with white outlines outside their respective internal color coding. The origin of muscles inserting around the orbit (blue) &amp; nose (purple) only are explained with line captions.*
![Color-coded frontal graphic shows muscles inserting around the upper lip (yellow), modiolus/angle of mouth (red), &amp; lower lip (magenta) marked with line captions. A tiny part of the lower aspect of the orbicularis oculi muscle is removed on the left to show the infraorbital origin of the levator labii superioris (LLS) underneath the orbicularis oculi. Zygomaticus minor (ZMi) is cut on right to show the underlying levator anguli oris (LAO) (also partially cut on right), originating from the canine fossa of the maxilla, seen underneath the cut midportion of LLS. Infraorbital neurovascular bundle courses in between LAO &amp; LLS &amp; is a potential route for perineural tumor spread from the face to the pterygopalatine fossa along the infraorbital canal.](images/app.statdx.com_image_thumbnail_4fa56bb3-7b81-446c-b31f-fee456065065_annotated_false_size_900_quality_90_81fcae70f7068848f6d28683d4217c647fdf1b17.jpg)
*Color-coded frontal graphic shows muscles inserting around the upper lip (yellow), modiolus/angle of mouth (red), &amp; lower lip (magenta) marked with line captions. A tiny part of the lower aspect of the orbicularis oculi muscle is removed on the left to show the infraorbital origin of the levator labii superioris (LLS) underneath the orbicularis oculi. Zygomaticus minor (ZMi) is cut on right to show the underlying levator anguli oris (LAO) (also partially cut on right), originating from the canine fossa of the maxilla, seen underneath the cut midportion of LLS. Infraorbital neurovascular bundle courses in between LAO &amp; LLS &amp; is a potential route for perineural tumor spread from the face to the pterygopalatine fossa along the infraorbital canal.*
![Origin of facial muscles painted on a 3D skull CT shows the muscles inserting around the upper lip (yellow), modiolus/angle of mouth (red), &amp; lower lip (magenta) marked with line captions. Buccinator muscle makes up the bulk of the cheek &amp; forms the lateral wall of the oral cavity; it is not classified as a muscle of facial mimicry. It originates on the alveolar processes of mandible &amp; maxilla near the molar teeth &amp; from the pterygomandibular raphe.](images/app.statdx.com_image_thumbnail_9af2d573-ab50-403a-9a9c-3c2937e23439_annotated_false_size_900_quality_90_c8f749061071c481b0052e8e89656fd86bba0dbc.jpg)
*Origin of facial muscles painted on a 3D skull CT shows the muscles inserting around the upper lip (yellow), modiolus/angle of mouth (red), &amp; lower lip (magenta) marked with line captions. Buccinator muscle makes up the bulk of the cheek &amp; forms the lateral wall of the oral cavity; it is not classified as a muscle of facial mimicry. It originates on the alveolar processes of mandible &amp; maxilla near the molar teeth &amp; from the pterygomandibular raphe.*
### Axial T1 MR
![The 1st of 3 coronal 3-mm T2 MR images from anterior to posterior shows the tiny compressor narium minor, DNA, and DNV, which do not have bony origins.](1bd34166-b9df-4885-b6d5-e8ae639aef50)
*The 1st of 3 coronal 3-mm T2 MR images from anterior to posterior shows the tiny compressor narium minor, DNA, and DNV, which do not have bony origins.*
![Coronal T2 MR though the soft tissues of the nose shows the depressor septi nasi originating in the maxillary incisive fossa; just laterally is the alar nasalis originating above the maxillary lateral incisor, &amp; further laterally is the transverse nasalis originating from the maxillary canine eminence. As their name implies, the depressor septi nasi inserts near the nasal septum into the medial crus of the greater alar cartilage, the alar nasalis lies anterior to the transverse nasalis &amp; inserts into the nasal alar lobule skin &amp; alar-facial crease, &amp; the transverse nasalis continues superiorly across the bridge of the nose.](caf24593-e3a1-48ac-b52f-4d47897eccc3)
*Coronal T2 MR though the soft tissues of the nose shows the depressor septi nasi originating in the maxillary incisive fossa; just laterally is the alar nasalis originating above the maxillary lateral incisor, &amp; further laterally is the transverse nasalis originating from the maxillary canine eminence. As their name implies, the depressor septi nasi inserts near the nasal septum into the medial crus of the greater alar cartilage, the alar nasalis lies anterior to the transverse nasalis &amp; inserts into the nasal alar lobule skin &amp; alar-facial crease, &amp; the transverse nasalis continues superiorly across the bridge of the nose.*
![Coronal T2 MR though the anterior orbital level shows the frontalis inserting at the scalp, along with the corrugator supercilii, depressor supercilii, procerus, &amp; orbicularis oculi, which are muscles inserting around the eye region. Intrinsic nasal muscles are functionally grouped as elevators, depressors, compressors, &amp; dilators. The procerus &amp; LLS alaeque nasi (LLSAN) are extrinsic nasal elevators.](69310e6f-ce9a-4639-8a78-e994c1750c1e)
*Coronal T2 MR though the anterior orbital level shows the frontalis inserting at the scalp, along with the corrugator supercilii, depressor supercilii, procerus, &amp; orbicularis oculi, which are muscles inserting around the eye region. Intrinsic nasal muscles are functionally grouped as elevators, depressors, compressors, &amp; dilators. The procerus &amp; LLS alaeque nasi (LLSAN) are extrinsic nasal elevators.*
![Axial 3-mm T1 MR series from superior to inferior is shown. MR at the forehead shows the corrugator supercilii originating from the frontal bone at the medial supraorbital rim &amp; lying deep to the frontalis to which it attaches. Note the temporoparietal fascia (TpF) (superficial fascia) merging with the frontalis muscle. The TpF is continuous with the galea aponeurotica in the scalp superiorly, frontalis muscle anteriorly, occipitalis muscle posteriorly, &amp; SMAS inferiorly. The SMAS (superficial fascia) is a continuous fibrous network connecting facial muscles to dermis, helping facial expressions, &amp; is continuous above with TpF as it passes over the zygomatic arch. The SMAS blends with the platysma muscle inferiorly &amp; begins fading medially as it reaches the lateral nasal margin. The SMAS is extremely thin beyond the anterior border of the masseter as it enters the cheek area &amp; is also so at its lower 1/2.](040d0964-71b8-47af-b8d2-87aa116c8cbe)
*Axial 3-mm T1 MR series from superior to inferior is shown. MR at the forehead shows the corrugator supercilii originating from the frontal bone at the medial supraorbital rim &amp; lying deep to the frontalis to which it attaches. Note the temporoparietal fascia (TpF) (superficial fascia) merging with the frontalis muscle. The TpF is continuous with the galea aponeurotica in the scalp superiorly, frontalis muscle anteriorly, occipitalis muscle posteriorly, &amp; SMAS inferiorly. The SMAS (superficial fascia) is a continuous fibrous network connecting facial muscles to dermis, helping facial expressions, &amp; is continuous above with TpF as it passes over the zygomatic arch. The SMAS blends with the platysma muscle inferiorly &amp; begins fading medially as it reaches the lateral nasal margin. The SMAS is extremely thin beyond the anterior border of the masseter as it enters the cheek area &amp; is also so at its lower 1/2.*
![Axial T1 MR at the topmost orbital level shows insertion of the procerus muscle into the skin &amp; frontalis muscle &amp; that of depressor supercilii muscle into the dermis. Also note the trochlea of the superior oblique muscle near its attachment on the superior nasal aspect of frontal bone.](c5dcbe47-2199-4f6f-b341-eb135df1d6ef)
*Axial T1 MR at the topmost orbital level shows insertion of the procerus muscle into the skin &amp; frontalis muscle &amp; that of depressor supercilii muscle into the dermis. Also note the trochlea of the superior oblique muscle near its attachment on the superior nasal aspect of frontal bone.*
![Axial T1 MR at the level of the eye lens shows the origin of the procerus muscle on the nasal bone (inserts around the orbit but also acts as a nasal elevator) &amp; depressor supercilii (inserts around the orbit) &amp; anomalous nasi (inserts at the nose) on the frontal process of the maxilla (FPM). Note the delineation of the superficial TpF, deep temporalis fascia, &amp; the loose areolar plane in between them; facial nerve branches at the temple lie in the fat of the loose areolar plane until 2 cm above the zygomatic arch and then pierce the TpF.](9d2104ec-e808-4ce4-b7ea-5455e5727353)
*Axial T1 MR at the level of the eye lens shows the origin of the procerus muscle on the nasal bone (inserts around the orbit but also acts as a nasal elevator) &amp; depressor supercilii (inserts around the orbit) &amp; anomalous nasi (inserts at the nose) on the frontal process of the maxilla (FPM). Note the delineation of the superficial TpF, deep temporalis fascia, &amp; the loose areolar plane in between them; facial nerve branches at the temple lie in the fat of the loose areolar plane until 2 cm above the zygomatic arch and then pierce the TpF.*
![Axial T1 MR just below the inferior orbital margin at the upper maxillary sinus level shows 2 main muscles inserting at the upper lip: The LLSAN, a nasal elevator also, to the nose anteriorly and upper lip posteriorly, &amp; the LLS. The LLSAN can be easily tracked down from its origin on FPM, a readily identifiable bony landmark. The LLS is shown just below its origin on the infraorbital margin above the infraorbital foramen; therefore, the infraorbital vessels and nerve run down deep to it over the maxilla. Superficial (SMAS, TpF) &amp; deep (parotidomasseteric fascia, temporalis fascia) fascial derivatives merging is shown.](b70a5555-5777-46b0-bd53-25ca34b3d812)
*Axial T1 MR just below the inferior orbital margin at the upper maxillary sinus level shows 2 main muscles inserting at the upper lip: The LLSAN, a nasal elevator also, to the nose anteriorly and upper lip posteriorly, &amp; the LLS. The LLSAN can be easily tracked down from its origin on FPM, a readily identifiable bony landmark. The LLS is shown just below its origin on the infraorbital margin above the infraorbital foramen; therefore, the infraorbital vessels and nerve run down deep to it over the maxilla. Superficial (SMAS, TpF) &amp; deep (parotidomasseteric fascia, temporalis fascia) fascial derivatives merging is shown.*
![Axial T1 MR at the lower zygomatic arch level shows the 3rd upper lip muscle, ZMi. ZMi is seen originating on the zygoma anterior to the origin of the zygomaticus major (ZMj), which attaches at the modiolus/angle of mouth. ZMi can be extremely thin unilaterally or bilaterally &amp; is thin on the right in this patient. Note retromaxillary fat pad, a part of buccal space.](6ed15b7f-7d7f-4a37-a1da-fa9de7e86ea2)
*Axial T1 MR at the lower zygomatic arch level shows the 3rd upper lip muscle, ZMi. ZMi is seen originating on the zygoma anterior to the origin of the zygomaticus major (ZMj), which attaches at the modiolus/angle of mouth. ZMi can be extremely thin unilaterally or bilaterally &amp; is thin on the right in this patient. Note retromaxillary fat pad, a part of buccal space.*
![Axial T1 MR just above the maxillary alveolus shows LAO muscle origin from the canine fossa of the maxilla. LAO is the deepest muscle seen anterior to the maxilla, &amp; this deep location can be used as a key identifier to separate this muscle (inserting into the modiolus/angle of mouth region) from the more superficial LLS &amp; LLSAN muscles (which can be traced toward their insertion in the upper lip). Infraorbital vessels &amp; nerves running down deep to the LLS now lie in between the LLS &amp; LAO, whereas the facial vessels run more laterally. The facial vein is larger &amp; has a more predictable course than the smaller but tortuous facial artery. A tiny buccal artery is seen. Note that the malar fat pad is subcutaneous in front of the cheek, whereas the buccal fat pad is deeper just outside the corners of the mouth.](97459ff1-5439-4442-877f-bb05c49dee91)
*Axial T1 MR just above the maxillary alveolus shows LAO muscle origin from the canine fossa of the maxilla. LAO is the deepest muscle seen anterior to the maxilla, &amp; this deep location can be used as a key identifier to separate this muscle (inserting into the modiolus/angle of mouth region) from the more superficial LLS &amp; LLSAN muscles (which can be traced toward their insertion in the upper lip). Infraorbital vessels &amp; nerves running down deep to the LLS now lie in between the LLS &amp; LAO, whereas the facial vessels run more laterally. The facial vein is larger &amp; has a more predictable course than the smaller but tortuous facial artery. A tiny buccal artery is seen. Note that the malar fat pad is subcutaneous in front of the cheek, whereas the buccal fat pad is deeper just outside the corners of the mouth.*
![Axial T1 MR at the maxillary alveolus level shows the parotid duct (PD) dividing the fat-filled buccal space into 2 compartments. The ZMj is seen anterior to the PD, or the risorius muscle originating from the SMAS anteriorly &amp; parotidomasseteric fascia posteriorly (prongs of forked line) could be confused for the PD. The PD pierces the buccinator muscle opposite the maxillary 2nd molar tooth. The buccal submucosal fat pad is seen as a thin, bright line lateral to the potential space of the oral cavity, whereas the maxillary alveolus buccal margin &amp; gum are seen as dark &amp; soft tissue lines medial to the oral cavity. The masseter muscle is part of the masticator space, &amp; buccinator muscle is part of the buccal space.](1456d7a5-6d18-42ce-b84b-a29c81f4c06e)
*Axial T1 MR at the maxillary alveolus level shows the parotid duct (PD) dividing the fat-filled buccal space into 2 compartments. The ZMj is seen anterior to the PD, or the risorius muscle originating from the SMAS anteriorly &amp; parotidomasseteric fascia posteriorly (prongs of forked line) could be confused for the PD. The PD pierces the buccinator muscle opposite the maxillary 2nd molar tooth. The buccal submucosal fat pad is seen as a thin, bright line lateral to the potential space of the oral cavity, whereas the maxillary alveolus buccal margin &amp; gum are seen as dark &amp; soft tissue lines medial to the oral cavity. The masseter muscle is part of the masticator space, &amp; buccinator muscle is part of the buccal space.*
![Axial T1 MR through the upper lip shows the orbicularis oris muscle making up the bulk of the lip. ZMj insertion is bifid, &amp; the LAO passes between its 2 heads at modiolar insertion (if not bifid, ZMj insertion is deep to LAO). The main insertion of deep muscle band of the ZMj is at the anterior margin of buccinator muscle/fascia (buccopharyngeal fascia); key for facial animation. Note risorius split fibers going toward modiolar insertion around depressor anguli oris (not shown) inferiorly.](1a7581ad-e15a-4798-a383-0e6bb535f53f)
*Axial T1 MR through the upper lip shows the orbicularis oris muscle making up the bulk of the lip. ZMj insertion is bifid, &amp; the LAO passes between its 2 heads at modiolar insertion (if not bifid, ZMj insertion is deep to LAO). The main insertion of deep muscle band of the ZMj is at the anterior margin of buccinator muscle/fascia (buccopharyngeal fascia); key for facial animation. Note risorius split fibers going toward modiolar insertion around depressor anguli oris (not shown) inferiorly.*
![Axial T1 MR through the lower lip shows the orbicularis oris muscle making up the bulk of the lip. The depressor anguli oris &amp; split trilaminar insertion of risorius around the DAO are seen. Risorius, an inconsistent muscle with most fibers originating from SMAS, some fibers from parotidomasseteric fascia, and, in some cases, receiving platysma muscle fibers, inserts at the modiolus in 3 distinct superficial, flush, &amp; deep layers in relation to DAO. Even though DAO prominently stands out at lower lip &amp; mandibular levels, it is not a muscle inserting at the lower lip. DAO can be traced superiorly to its modiolar insertion. The mandibular alveolus buccal margin &amp; gum line are seen as a dark line &amp; soft tissue intensity, respectively, medial to the potential space of the oral cavity.](7c60fda6-fa61-48d3-b541-08a63f0b1fd7)
*Axial T1 MR through the lower lip shows the orbicularis oris muscle making up the bulk of the lip. The depressor anguli oris &amp; split trilaminar insertion of risorius around the DAO are seen. Risorius, an inconsistent muscle with most fibers originating from SMAS, some fibers from parotidomasseteric fascia, and, in some cases, receiving platysma muscle fibers, inserts at the modiolus in 3 distinct superficial, flush, &amp; deep layers in relation to DAO. Even though DAO prominently stands out at lower lip &amp; mandibular levels, it is not a muscle inserting at the lower lip. DAO can be traced superiorly to its modiolar insertion. The mandibular alveolus buccal margin &amp; gum line are seen as a dark line &amp; soft tissue intensity, respectively, medial to the potential space of the oral cavity.*
![Axial T1 MR at lower mandible level shows muscles inserting at the lower lip, namely, depressor labii inferioris, mentalis, &amp; platysma. Platysma originates from the superficial pectoral &amp; deltoid fascia, inserts on inferior body of mandible, skin, &amp; hypodermis, &amp; is continuous with SMAS in face. Some fibers of DAO may continue below mental tubercle, joining contralateral DAO &amp; creating transversus menti muscle.](939d6fa7-a60e-4527-a581-0a7c181cdaba)
*Axial T1 MR at lower mandible level shows muscles inserting at the lower lip, namely, depressor labii inferioris, mentalis, &amp; platysma. Platysma originates from the superficial pectoral &amp; deltoid fascia, inserts on inferior body of mandible, skin, &amp; hypodermis, &amp; is continuous with SMAS in face. Some fibers of DAO may continue below mental tubercle, joining contralateral DAO &amp; creating transversus menti muscle.*
### Coronal T1 MR
![Coronal T1 MR shows fascial reflections. In the face, muscles insert directly into the dermis via the SMAS, facilitating facial expression (in the rest of the body, an investing layer of fascia separates muscle from subcutaneous tissue). The SMAS is continuous above with the TpF (a.k.a. superficial temporal fascia) as it passes over the zygomatic arch, which, in turn, is continuous with galea aponeurotica in the scalp superiorly, frontalis muscle anteriorly, &amp; occipitalis muscle posteriorly. Parotidomasseteric fascia (deep fascia in the cheek deep to the SMAS) is continuous above with temporalis fascia (a.k.a. deep temporal fascia), which, in turn, covers the temporalis muscle, splits over the zygomatic arch superficial &amp; deep surfaces inferiorly, &amp; attaches to the pericranium at &amp; above the superior temporal line on the skull superiorly. The facial nerve branches in the parotid gland lie deep underneath parotideomasseteric fascia, then in the loose areolar tissue plane between the TpF &amp; zygomatic arch, in the loose areolar plane between the superficial TpF &amp; deep temporalis fascia ~ 1 cm above the zygomatic arch, &amp; penetrates TpF ~ 2 cm above the zygomatic arch to run along the superficial temporal artery.](be2b20a1-bcb4-4403-8ca5-1b33c6efb80b)
*Coronal T1 MR shows fascial reflections. In the face, muscles insert directly into the dermis via the SMAS, facilitating facial expression (in the rest of the body, an investing layer of fascia separates muscle from subcutaneous tissue). The SMAS is continuous above with the TpF (a.k.a. superficial temporal fascia) as it passes over the zygomatic arch, which, in turn, is continuous with galea aponeurotica in the scalp superiorly, frontalis muscle anteriorly, &amp; occipitalis muscle posteriorly. Parotidomasseteric fascia (deep fascia in the cheek deep to the SMAS) is continuous above with temporalis fascia (a.k.a. deep temporal fascia), which, in turn, covers the temporalis muscle, splits over the zygomatic arch superficial &amp; deep surfaces inferiorly, &amp; attaches to the pericranium at &amp; above the superior temporal line on the skull superiorly. The facial nerve branches in the parotid gland lie deep underneath parotideomasseteric fascia, then in the loose areolar tissue plane between the TpF &amp; zygomatic arch, in the loose areolar plane between the superficial TpF &amp; deep temporalis fascia ~ 1 cm above the zygomatic arch, &amp; penetrates TpF ~ 2 cm above the zygomatic arch to run along the superficial temporal artery.*
### Additional Images
![Muscle groups with color-coding according to the insertion site are shown. Muscles of facial mimicry originate on bone and insert into the dermis through the SMAS; exceptions are inconsistently found in the risorius &amp; malaris muscles that originate and insert in soft tissue &amp; also in tiny nasal muscles, namely, the compressor narium minor &amp; dilator naris anterior (both originate from nasal cartilages and insert into skin) &amp; dilator naris vestibularis (originate &amp; insert into skin). Note that the buccinator muscle makes up the bulk of the cheek &amp; forms the lateral wall of oral cavity. It is not classified as a muscle of facial mimicry, as it originates on the alveolar processes of the mandible &amp; maxilla near molar teeth &amp; the pterygomandibular raphe &amp; inserts around the mouth; medial fibers decussate &amp; merge with the upper and lower lip muscles.](a2de1adb-efc7-43ca-90ff-482881ea5a40)
*Muscle groups with color-coding according to the insertion site are shown. Muscles of facial mimicry originate on bone and insert into the dermis through the SMAS; exceptions are inconsistently found in the risorius &amp; malaris muscles that originate and insert in soft tissue &amp; also in tiny nasal muscles, namely, the compressor narium minor &amp; dilator naris anterior (both originate from nasal cartilages and insert into skin) &amp; dilator naris vestibularis (originate &amp; insert into skin). Note that the buccinator muscle makes up the bulk of the cheek &amp; forms the lateral wall of oral cavity. It is not classified as a muscle of facial mimicry, as it originates on the alveolar processes of the mandible &amp; maxilla near molar teeth &amp; the pterygomandibular raphe &amp; inserts around the mouth; medial fibers decussate &amp; merge with the upper and lower lip muscles.*
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title: "Frontal Recess and Related Air Cells"
docid: "f96e79b9-f0cf-4b43-aaf7-4453e8a36664"
authors:
- key: "b2e6dabb-ee1c-42a4-a332-9f0814c1c607"
value: "Surjith Vattoth, MD"
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name: "Frontal Recess and Related Air Cells"
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lastUpdated: "02/20/24"
pageDescription: "Frontal Recess and Related Air Cells"
pageKeywords: "Head and Neck, Anatomy, Nose and Sinuses, Frontal Recess and Related Air Cells"
pageTitle: "Frontal Recess and Related Air Cells | STATdx"
enhancedTitle: "Frontal Recess and Related Air Cells"
type: "ANATOMY"
breadcrumbs:
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- "Anatomy"
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---
## TERMINOLOGY
- ### Abbreviations
- Frontal recess (FR); agger nasi cell (AN); ethmoid bulla (EB); suprabullar cell (SBC); frontal bullar cell (FBC); supraorbital ethmoid cell (SOEC); anterior ethmoidal artery (AEA)
- ### Definitions
- **FR**: Frontal sinus drainage pathway (FSDP) (inverted funnel shape) bordered anteriorly by AN & FR Kuhn cells, posteriorly by bulla ethmoidalis, FBCs, & SBCs, & posterolaterally by SOECs
## IMAGING ANATOMY
- ### Overview
- **Frontal sinus** lies within frontal bone (right & left sinuses develop independently) with thick anterior table & thinner posterior table; medial wall intersinus septum; thin floor corresponds to anterior aspect of orbital roof
- Thin posterior wall & floor can be eroded by mucocele
- Funnel-shaped posteroinferomedial aspect of frontal sinus (often called **frontal infundibulum**) superiorly & inverted funnel-shaped FR inferiorly likened to hourglass with its waist in between at frontal sinus ostium
- **Frontal beak****(****nasofrontal process****)** forms floor of inferior frontal sinus & is identifier for anterior landmark of **frontal sinus ostium**
- FR formed by opposition of adjacent air cells at anteroinferior aspect of frontal bone superiorly & anterosuperior aspect of ethmoid bone inferiorly
- Upper border of FR by frontal sinus ostium; inferior drainage from FR can be either to **middle meatus** directly or via **ethmoid infundibulum**
- ### Extent
- If uncinate process turns laterally to insert on **lamina papyracea**, FR drains into middle meatus directly, & ethmoid infundibulum is closed superiorly by blind-ending pouch called **recessus terminalis**
- If uncinate process turns medially to insert on **middle turbinate** or runs superiorly to insert on **skull base**, FR drains into ethmoid infundibulum & then middle meatus
- ### Anatomy Relationships
- Anteriorly: AN below & Kuhn cells above
- Laterally: Lamina papyracea (or intervening AN & Kuhn cells when present)
- Posterolaterally: SOECs when present
- Medially: Middle turbinate vertical portion
- Posteriorly: EB, SBCs, & FBCs when present
- ### Internal Contents
- **Middle & posterior portions of basal lamella of middle turbinate**: Extend laterally to join lamina papyracea & divide anterior from posterior ethmoid air cells
- Vertical portion of basal lamella attaches to cribriform plate of ethmoid & is best seen in coronal CT; very delicate, & its detachment at surgery in this region could damage dura with resultant CSF leak
- EB, SBCs, & FBCs are intramural anterior ethmoid air cells anterior to basal lamella of middle turbinate & form posterior boundary of FR
- Posterior margin of basal lamella attaches to perpendicular plate of palatine bone
- **EB (bulla ethmoidalis)**: Dominant anterior ethmoid air cell formed by pneumatization of bulla lamella (seen anterior to basal lamella of middle turbinate)
- Forms lateral margin of ethmoid infundibulum & posterior margin of FR
- **SBCs**: Anterior ethmoid cells seen above EB; extends behind FR but lies entirely below level of frontal sinus ostium (no extension into frontal sinus)
- SBC superior wall: **Skull base**
- CT correlate of suprabullar recess; seen as cleft above EB when viewed endoscopically
- **Suprabullar & retrobullar recesses**: Previously less correctly called **sinus lateralis** or **lateral sinus of Grunwald**
- Located between ethmoid roof superiorly, EB anteriorly & inferiorly, lamina papyracea laterally, & basal lamella of middle turbinate posteriorly
- Recesses typically separated by bony crest or mucosal projection from basal lamella of middle turbinate to EB
- Recesses communicate medially with middle meatus through hiatus semilunaris superior
- Suprabullar recess separated from FR by bulla lamella/EB reaching & attaching to skull base; 2 recesses do not typically communicate with FR
- FR may rarely drain directly into suprabullar recess when bulla lamella/EB does not extend to skull base
- **AEA**at roof of suprabullar recess in majority (85%)
- **FBCs**: Anterior ethmoid cells above EB; extends behind FR & **also into frontal sinus** above frontal sinus ostium
- FBC posterosuperior wall: **Skull base**
- Both SBCs & FBCs may be mistaken for skull base during endoscopic surgery → incomplete surgical dissection
- SBC/FBC presence should be determined before surgery by assessing preoperative scans
- **SOECs**: Anterior ethmoid air cells extending superolaterally over orbit from FR & seen posterolateral to FR
- Posterior wall:**Skull base**
- Pneumatization of orbital plate of frontal bone posterior to frontal sinus & posterolateral to FR
- SOEC ostium can be mistaken for frontal sinus ostium during functional endoscopic sinus surgery (FESS)
- Transillumination of **SOECs**with telescope during FESS shows transmitted **light in inner canthal area**, while that of frontal sinus shows light in supraorbital area
- Drain into lateral aspect of FR; SOEC ostium seen just anterior to AEA canal on sequential coronal CT images
- **SOECs** can be mistaken for **septated frontal sinus** on coronal images
- **SOECs**can be differentiated by their location posterior to frontal sinus separated by **horizontally oriented septum**on **axial**images
- **AEA** runs in **anterior ethmoidal notch (foramen)** along medial orbital wall (lamina papyracea); crosses anterior ethmoid air cells in bony **anterior ethmoidal canal**
- AEA enters anterior cranial fossa at point in lateral lamella of cribriform plate called **ethmoidal sulcus**
- AEA found endoscopically by tracing anterior wall of EB towards ethmoid roof; 11 mm (range 6-15 mm) behind posterior wall of FR (in suprabullar recess in 85%)
- AEA usually in contact with skull base, can be 1-3 mm below skull base within bony mesentery
- **Anterior ethmoidal canal** ~ 8 mm in length; 40% show partial or total bony dehiscence, especially inferiorly
- **AEA** runs obliquely in skull base behind anterior wall of EB where skull base turns from vertical (posterior frontal sinus wall) to horizontal (cribriform plate of ethmoid)
- **Intact bulla technique** for FR surgery can protect AEA
- If anterior wall of EB does not reach skull base with presence of suprabullar recess, then AEA may be damaged even with intact bulla technique
- **SOECs** immediately above anterior ethmoidal notch/canal/sulcus predisposes **AEA at risk during FESS**
- AEA travels freely in ethmoid sinus/suprabullar recess
- If no SOECs, anterior ethmoidal notch/canal/sulcus abuts fovea ethmoidalis/lateral lamella of cribriform plate
- AEA considered relatively protected during FESS
- AEA injury → rapidly enlarging retroorbital hematoma due to retraction of transected artery into orbit
- Cut AEA should be prophylactically cauterized to avoid enlarging orbital hematoma
- **Posterior ethmoidal artery** ~ 10 mm behind AEA
- **Interfrontal sinus septal cell**: Pneumatized interfrontal sinus septum; can extend into crista galli when extensive
- Drains into medial aspect of FR
- Can obstruct frontal sinus ostium
- **AN**: Latin for nasal mound
- Most anterior ethmoid air cell that involves **lacrimal bone** or **frontal process of maxilla**
- Forms anterior & lateral **boundary of FR inferiorly**
- Key to surgical access to FR
- Open AN & palpate with probe to identify posterior wall of frontal sinus away from & in front of AEA for good, safe visualization of frontal sinus
- **FR Kuhn cells**: Anterior & lateral **boundary of FR superiorly**
- **Types 1-3**Kuhn cells: FR air cells seen **above AN** (type 1 single & type 2 multiple in FR, & type 3 single reaching sinus), but **t****ype 4** single isolated cell within frontal sinus **not abutting AN**
- Type 1: Single cell above AN
- Posterior wall: Free partition in FR
- Type 2: Tier of 2 or more cells above AN
- Posterior wall: Free partition in FR
- Type 3: Single large cell above AN; extends superiorly into frontal infundibulum/sinus proper
- Posterior wall: Free partition in FR **& frontal sinus**
- FBCs also extend from FR into frontal sinus & cannot be differentiated in coronal CT from type 3 Kuhn cell
- **FBCs (posterior to FR)** sagittal CT: **Skull base** forms **posterosuperior wall**
- **Type 3 Kuhn cells (anterior to FR)** sagittal CT: **Free partition in frontal sinus & FR** forms posterosuperior wall with air gap of frontal sinus/recess between type 3 Kuhn cells & skull base
- Type 4: Rare, isolated cell in frontal sinus; **anterior table or floor of frontal sinus** forms anterior/inferior margin
- Free partition in frontal sinus forms posterior wall
- Called "cell within cell"; sometimes isolated aerated type 4 cell may be seen with opacification of surrounding diseased frontal sinus
- **Modified Kuhn classification** defines type 3 cell as extending up from FR above frontal beak but < 50% of vertical height of frontal sinus, whereas type 4 cell extends from FR into frontal sinus > 50% of its height
- **International frontal sinus anatomy classification (IFAC)**
- **Anterior cells**: Push FSDP medially, posteriorly, or posteromedially
- AN, supraagger cell (corresponds to types 1 & 2 Kuhn cells) & supraagger frontal cell (corresponds to types 3 & 4 Kuhn cells))
- **Posterior cells**: Push FSDP anteriorly
- SBC, suprabulla frontal cell (corresponds to FBC), & SOEC
- **Medial cells**: Push FSDP laterally
- Frontal septal cell (corresponds to interfrontal sinus septal cell)
## ANATOMY IMAGING ISSUES
- ### Imaging Recommendations
- Unenhanced,thin 0.625-mm volumetric images with sagittal & coronal reconstructions at 1- to 2-mm intervals
- Both high-resolution bone & soft tissue algorithm reconstructions in all 3 planes
- No gantry tilt; include ears, entire maxilla, tip of nose, chin & frontal sinuses to ensure compatibility with FESS image navigation guidance systems
- ### Imaging Pitfalls
- Sagittal images to be reviewed in addition to coronal & axial images for FR anatomy & presence/disease of AN & Kuhn cells anteriorly; intersinus septal cell medially; EB, SBCs, FBCs posteriorly, & SOECs posterolaterally
- Failure to identify may lead to incomplete failed FESS in FR
## CLINICAL IMPLICATIONS
- ### Clinical Importance
- Primary surgery of FR usually avoided initially; anterior ethmoid/ostiomeatal unit (OMU) primary surgery done 1st
- To reduce risk of injury to critical structures adjacent to FR, such as orbit, AEA, & anterior skull base, & due to susceptibility of FR region to postsurgical scar formation
- Frontal sinus surgeries mostly revision procedures after failed OMU surgeries, such as uncinectomy, anterior ethmoidectomy, middle meatal antrostomy, & septoplasty
- Anterior ethmoid/OMU surgeries usually enough to clear FR & frontal sinus disease
- Small **size of FR** limits enlargement of FSDP during frontal sinus FESS & more extensive frontal sinusotomy will have to be done
- Size of FR should be evaluated on preoperative scans
- Frontal beak (nasofrontal process) anterior to frontal sinus ostium has no important structures; drilling anterior to frontal ostium with angled burr relatively safe
- Posterior margin of frontal sinus ostium should be never breached due to its close relationship with cribriform plate & anterior cranial fossa
- **Inadequate removal**of air cells in relation to FR is most common cause of failed frontal FESS: AN or other anterior (Kuhn), medial (intersinus cell), posterior (EB, SBC, FBC), or posterolateral (SOEC)
- Residual air cells obstruct FR & also serve as scaffold for scar tissue formation
- Disease in recessus terminalis in cases where inferior FR drains into middle meatus directly (when uncinate process turns laterally to insert on lamina papyracea) can displace uncinate process medially towards FR
- **Retained medialized uncinate process** predisposes to FR restenosis after FESS
- **Lateralized middle turbinate** amputated anterior stump may obstruct FR after FESS
- **Bolgerization**: Process of medialization of middle turbinate by surgically creating small abrasions on its medial aspect & adjacent nasal septum to correct floppy lateralized middle turbinate rather than resecting it
- Medialized middle turbinate normal expected postsurgical finding in this scenario
747a66cd-d97c-4b56-b205-2aa227f16889
## Images
### Coronal and Sagittal Graphics of Types 1 & 2 Kuhn Cells
![Graphics show frontal sinus drainage pathway anatomy &amp; a right type 1 Kuhn frontal cell (supraagger cell [SAC] as per International Frontal Sinus Anatomy Classification [IFAC]). Frontal sinus drainage is through a funnel-shaped posteroinferomedial frontal sinus (frontal infundibulum) superiorly &amp; an inverted funnel-shaped frontal recess (FR) inferiorly; together they resemble an hourglass with a waist in between at the frontal sinus ostium. Frontal beak (nasofrontal process) forms the inferior frontal sinus floor &amp; serves as the anterior landmark of the frontal sinus ostium. FR is bordered anterolaterally by agger nasi &amp; FR Kuhn cells, posteriorly by bulla ethmoidalis, frontal bullar, &amp; suprabullar cells, &amp; posterolaterally by supraorbital ethmoid cells (SOEC). The upper border of the FR is the frontal sinus ostium, &amp; its inferior drainage can be either directly to the middle meatus or via ethmoid infundibulum according to attachment pattern of uncinate process. Type 1 Kuhn cell is a single cell above agger nasi.](images/app.statdx.com_image_thumbnail_e1921f3c-9b57-46ba-bfd7-1f8bcf3efbcc_size_174_quality_85_34bba595bf746f83ed1fa568936f762a2d8df7ee.jpg)
*Graphics show frontal sinus drainage pathway anatomy &amp; a right type 1 Kuhn frontal cell (supraagger cell [SAC] as per International Frontal Sinus Anatomy Classification [IFAC]). Frontal sinus drainage is through a funnel-shaped posteroinferomedial frontal sinus (frontal infundibulum) superiorly &amp; an inverted funnel-shaped frontal recess (FR) inferiorly; together they resemble an hourglass with a waist in between at the frontal sinus ostium. Frontal beak (nasofrontal process) forms the inferior frontal sinus floor &amp; serves as the anterior landmark of the frontal sinus ostium. FR is bordered anterolaterally by agger nasi &amp; FR Kuhn cells, posteriorly by bulla ethmoidalis, frontal bullar, &amp; suprabullar cells, &amp; posterolaterally by supraorbital ethmoid cells (SOEC). The upper border of the FR is the frontal sinus ostium, &amp; its inferior drainage can be either directly to the middle meatus or via ethmoid infundibulum according to attachment pattern of uncinate process. Type 1 Kuhn cell is a single cell above agger nasi.*
![Graphics show type 2 Kuhn cells (SAC as per IFAC), a tier of 2 or more cells above agger nasi. Posterior walls of both types 1 &amp; 2 Kuhn cells are free partitions in the FR.](images/app.statdx.com_image_thumbnail_945ba088-15fc-403f-ae0f-3a6ebae965c9_annotated_false_size_900_quality_90_a729ff7601043e0291e722208a91db117bafd0f1.jpg)
*Graphics show type 2 Kuhn cells (SAC as per IFAC), a tier of 2 or more cells above agger nasi. Posterior walls of both types 1 &amp; 2 Kuhn cells are free partitions in the FR.*
### Coronal and Sagittal Graphics of Types 3 & 4 Kuhn Cells
![Graphics show a type 3 Kuhn frontal cell (SAC frontal cell [SAFC] as per IFAC), a single large cell above agger nasi. It extends superiorly beyond the FR into the frontal infundibulum/sinus proper. Posterior wall of a type 3 cell is a free partition in the FR &amp; frontal sinus.](66f47af8-36ab-4ed8-b609-989caf92f068)
*Graphics show a type 3 Kuhn frontal cell (SAC frontal cell [SAFC] as per IFAC), a single large cell above agger nasi. It extends superiorly beyond the FR into the frontal infundibulum/sinus proper. Posterior wall of a type 3 cell is a free partition in the FR &amp; frontal sinus.*
![Graphics show a type 4 Kuhn frontal cell (SAFC as per IFAC), a rare, isolated cell in the frontal sinus. Its anterior or inferior margin is formed by the anterior table or floor of the frontal sinus, &amp; the posterior wall is a free partition in the frontal sinus. Note that types 1-3 Kuhn cells are FR air cells seen above agger nasi (type 1 single &amp; type 2 multiple in FR, &amp; type 3 single reaching sinus) &amp; form the anterior and lateral boundary of the FR superiorly, whereas type 4 is a single isolated cell within the frontal sinus not abutting agger nasi air cell.](images/app.statdx.com_image_thumbnail_a38accbd-ef2a-4362-a6a5-79664bb4b877_annotated_false_size_900_quality_90_dc384255017fc0e827b3c2e0d01b1e8f53c9080f.jpg)
*Graphics show a type 4 Kuhn frontal cell (SAFC as per IFAC), a rare, isolated cell in the frontal sinus. Its anterior or inferior margin is formed by the anterior table or floor of the frontal sinus, &amp; the posterior wall is a free partition in the frontal sinus. Note that types 1-3 Kuhn cells are FR air cells seen above agger nasi (type 1 single &amp; type 2 multiple in FR, &amp; type 3 single reaching sinus) &amp; form the anterior and lateral boundary of the FR superiorly, whereas type 4 is a single isolated cell within the frontal sinus not abutting agger nasi air cell.*
### Coronal and Sagittal Graphics of Suprabullar Cells & Bullar Cells
![Sagittal graphic shows a suprabullar cell ([SBC] as per IFAC), which are anterior ethmoid air cells seen above the bulla ethmoidalis extending behind the FR &amp; lying entirely below the level of frontal sinus ostium (with no extension into the frontal sinus); its superior wall is the skull base. An SBC is the CT scan correlate of a suprabullar recess, which is seen as a cleft above the ethmoid bulla when viewed endoscopically. Suprabullar &amp; retrobullar recesses were previously known as sinus lateralis or the lateral sinus of Grunwald. The anterior ethmoidal artery is located at the roof of the suprabullar recess in the majority (85%).](7be259a7-eb14-4195-a76c-f6f8f1a8fa7f)
*Sagittal graphic shows a suprabullar cell ([SBC] as per IFAC), which are anterior ethmoid air cells seen above the bulla ethmoidalis extending behind the FR &amp; lying entirely below the level of frontal sinus ostium (with no extension into the frontal sinus); its superior wall is the skull base. An SBC is the CT scan correlate of a suprabullar recess, which is seen as a cleft above the ethmoid bulla when viewed endoscopically. Suprabullar &amp; retrobullar recesses were previously known as sinus lateralis or the lateral sinus of Grunwald. The anterior ethmoidal artery is located at the roof of the suprabullar recess in the majority (85%).*
![Sagittal graphic shows a frontal bullar cell (FBC). FBCs (suprabulla frontal cell [SBFC] as per IFAC) are also anterior ethmoid air cells above the bulla ethmoidalis extending behind the FR, but unlike SBCs, extend into the frontal sinus above frontal sinus ostium; its posterosuperior wall is also the skull base. Both SBCs and SBFCs may be mistaken for the skull base during endoscopic surgery, resulting in incomplete surgical dissection. Their presence should be determined before surgery by assessing preoperative scans.](17f6bf63-8163-49c3-b831-cec2a24b618d)
*Sagittal graphic shows a frontal bullar cell (FBC). FBCs (suprabulla frontal cell [SBFC] as per IFAC) are also anterior ethmoid air cells above the bulla ethmoidalis extending behind the FR, but unlike SBCs, extend into the frontal sinus above frontal sinus ostium; its posterosuperior wall is also the skull base. Both SBCs and SBFCs may be mistaken for the skull base during endoscopic surgery, resulting in incomplete surgical dissection. Their presence should be determined before surgery by assessing preoperative scans.*
### Coronal Graphics
![Coronal graphic shows the anterior ethmoidal notch/canal/sulcus (containing the anterior ethmoid artery) abutting the fovea ethmoidalis/lateral lamella of the cribriform plate. The anterior ethmoid artery is considered relatively protected during functional endoscopic sinus surgery (FESS) with this anatomy.](aaf1ba14-aa63-4129-b3b4-dd705ab38bb6)
*Coronal graphic shows the anterior ethmoidal notch/canal/sulcus (containing the anterior ethmoid artery) abutting the fovea ethmoidalis/lateral lamella of the cribriform plate. The anterior ethmoid artery is considered relatively protected during functional endoscopic sinus surgery (FESS) with this anatomy.*
![Coronal graphic shows supraorbital ethmoid cells [(SOECs) as per IFAC] immediately above the anterior ethmoidal notch/canal/sulcus. This anatomy predisposes anterior ethmoid artery injury risk during FESS, since the artery travels freely within the air cells, ethmoid sinus/suprabullar recess. SOECs are anterior ethmoid air cells that extend superolaterally over the orbit from the FR &amp; are seen posterolateral to the FR. They are formed by pneumatization of the orbital plate of the frontal bone posterior to the frontal sinus &amp; posterolateral to FR. SOECs drain into the lateral aspect of the FR; SOEC ostium is seen just anterior to the anterior ethmoidal artery canal in sequential coronal CT images. The ostium can be mistaken for the frontal sinus ostium during FESS.](dc2d6170-87b0-4cea-b841-b34d906ff3d6)
*Coronal graphic shows supraorbital ethmoid cells [(SOECs) as per IFAC] immediately above the anterior ethmoidal notch/canal/sulcus. This anatomy predisposes anterior ethmoid artery injury risk during FESS, since the artery travels freely within the air cells, ethmoid sinus/suprabullar recess. SOECs are anterior ethmoid air cells that extend superolaterally over the orbit from the FR &amp; are seen posterolateral to the FR. They are formed by pneumatization of the orbital plate of the frontal bone posterior to the frontal sinus &amp; posterolateral to FR. SOECs drain into the lateral aspect of the FR; SOEC ostium is seen just anterior to the anterior ethmoidal artery canal in sequential coronal CT images. The ostium can be mistaken for the frontal sinus ostium during FESS.*
### Sagittal and Coronal Bone CT
![Sagittal CT shows the frontal sinus drainage pathway, which is likened to an hourglass with the superior part formed by the funnel-shaped posteroinferomedial frontal sinus &amp; inferior part by the inverted funnel-shaped FR; the waist of the hourglass is at frontal sinus ostium level. The frontal beak (the nasofrontal process) is the anterior landmark of the frontal sinus ostium. The FR is bordered anterolaterally by agger nasi &amp; Kuhn cells (no Kuhn cells are present here).](a3e5b015-e5a3-4522-93b8-9718addf4e74)
*Sagittal CT shows the frontal sinus drainage pathway, which is likened to an hourglass with the superior part formed by the funnel-shaped posteroinferomedial frontal sinus &amp; inferior part by the inverted funnel-shaped FR; the waist of the hourglass is at frontal sinus ostium level. The frontal beak (the nasofrontal process) is the anterior landmark of the frontal sinus ostium. The FR is bordered anterolaterally by agger nasi &amp; Kuhn cells (no Kuhn cells are present here).*
![Coronal bone NECT shows inferior drainage of the FR. If the uncinate process (UP) turns laterally to insert on the lamina papyracea, the FR drains into the middle meatus directly, &amp; the ethmoid infundibulum is closed superiorly by a blind-ending pouch called &quot;recessus terminalis,&quot; as seen on the right side of this patient.](8e2728c8-066c-4000-8db3-f8abeac14aed)
*Coronal bone NECT shows inferior drainage of the FR. If the uncinate process (UP) turns laterally to insert on the lamina papyracea, the FR drains into the middle meatus directly, &amp; the ethmoid infundibulum is closed superiorly by a blind-ending pouch called &quot;recessus terminalis,&quot; as seen on the right side of this patient.*
![Coronal bone NECT shows inferior drainage of the FR. If the UP runs superiorly to insert on the skull base (labeled on the right side of this patient) or turns medially to insert on middle turbinate (labeled on left side of this patient), the FR drains into the ethmoid infundibulum &amp; then the middle meatus.](4a57d4f5-b166-458b-9e31-15d218a50771)
*Coronal bone NECT shows inferior drainage of the FR. If the UP runs superiorly to insert on the skull base (labeled on the right side of this patient) or turns medially to insert on middle turbinate (labeled on left side of this patient), the FR drains into the ethmoid infundibulum &amp; then the middle meatus.*
### Sagittal Bone CT
![Sagittal CT shows a type 1 Kuhn cell, a single cell above agger nasi.](82767e85-7fdb-4378-afa8-d5035984d3fe)
*Sagittal CT shows a type 1 Kuhn cell, a single cell above agger nasi.*
![Sagittal CT shows type 2 Kuhn frontal cells. Kuhn cells form the anterior &amp; lateral boundary of the superior aspect of FR. Types 1-3 Kuhn cells are FR air cells just above agger nasi, but type 4 is a single, isolated cell within the frontal sinus not abutting agger nasi. Type 1 is single &amp; type 2 are multiple cells in the FR, whereas a type 3 cell is a single air cell in FR extending superiorly into the frontal infundibulum/frontal sinus proper.](459a36bd-b585-4c3c-b580-dfa3798062c8)
*Sagittal CT shows type 2 Kuhn frontal cells. Kuhn cells form the anterior &amp; lateral boundary of the superior aspect of FR. Types 1-3 Kuhn cells are FR air cells just above agger nasi, but type 4 is a single, isolated cell within the frontal sinus not abutting agger nasi. Type 1 is single &amp; type 2 are multiple cells in the FR, whereas a type 3 cell is a single air cell in FR extending superiorly into the frontal infundibulum/frontal sinus proper.*
![Sagittal CT shows a type 3 Kuhn frontal cell. Its posterior wall is a free partition in FR &amp; frontal infundibulum/frontal sinus &amp; can narrow these structures from the anterior aspect. In contrast, the frontal bullar cell narrows the FR &amp; frontal infundibulum/frontal sinus from its posterior aspect; a suprabullar cell narrows only the FR from the posterior aspect.](51b37ba2-8c23-40b6-853d-462c9b9d3dfc)
*Sagittal CT shows a type 3 Kuhn frontal cell. Its posterior wall is a free partition in FR &amp; frontal infundibulum/frontal sinus &amp; can narrow these structures from the anterior aspect. In contrast, the frontal bullar cell narrows the FR &amp; frontal infundibulum/frontal sinus from its posterior aspect; a suprabullar cell narrows only the FR from the posterior aspect.*
### Sagittal & Coronal Bone CT
![Sagittal CT shows a type 4 Kuhn cell, a rare, isolated cell in the frontal sinus. Its anterior/inferior margin is the anterior table/floor of the frontal sinus; the posterior wall is a free partition in that sinus. Note that the modified Kuhn classification defines a type 3 cell as extending up from the FR above the frontal beak but &lt; 50% of vertical height of the frontal sinus, whereas a type 4 cell extends from the FR into the frontal sinus &gt; 50% of its height.](77404d5e-ac89-4adb-9d8f-9307c63a1ab3)
*Sagittal CT shows a type 4 Kuhn cell, a rare, isolated cell in the frontal sinus. Its anterior/inferior margin is the anterior table/floor of the frontal sinus; the posterior wall is a free partition in that sinus. Note that the modified Kuhn classification defines a type 3 cell as extending up from the FR above the frontal beak but &lt; 50% of vertical height of the frontal sinus, whereas a type 4 cell extends from the FR into the frontal sinus &gt; 50% of its height.*
![Coronal bone NECT shows a right type 3 FR Kuhn cell extends superiorly beyond the FR into the frontal infundibulum/sinus proper, &amp; multiple left type 2 FR Kuhn cells lie below the frontal sinus ostium. Types 1-3 Kuhn cells lie lateral to the FR, just above agger nasi.](6d64f210-55a7-4391-b9e2-247755583a6e)
*Coronal bone NECT shows a right type 3 FR Kuhn cell extends superiorly beyond the FR into the frontal infundibulum/sinus proper, &amp; multiple left type 2 FR Kuhn cells lie below the frontal sinus ostium. Types 1-3 Kuhn cells lie lateral to the FR, just above agger nasi.*
![Coronal bone NECT shows an interfrontal sinus septal cell (frontal septal cell [FSC] as per IFAC); it can extend into crista galli when extensive, drains into the medial aspect of the FR, &amp; can obstruct the frontal sinus ostium. Also shown is a left type 4 Kuhn cell.](285d2b28-dc41-446d-8ca1-f83e98db77c0)
*Coronal bone NECT shows an interfrontal sinus septal cell (frontal septal cell [FSC] as per IFAC); it can extend into crista galli when extensive, drains into the medial aspect of the FR, &amp; can obstruct the frontal sinus ostium. Also shown is a left type 4 Kuhn cell.*
### Sagittal & Coronal Bone CT of Frontal Bullar Cell Type 3 Kuhn cell
![Right parasagittal bone NECT shows a right FBC. On sagittal images, the posterosuperior wall of an FBC (posterior to frontal sinus/recess) is formed by the skull base.](00d64d0f-69db-4a86-9d59-21f32fc0d096)
*Right parasagittal bone NECT shows a right FBC. On sagittal images, the posterosuperior wall of an FBC (posterior to frontal sinus/recess) is formed by the skull base.*
![Coronal NECT in the same patient shows a right FBC (confirmed by right parasagittal CT images) &amp; a larger left type 3 Kuhn cell (confirmed by evaluating left parasagittal CT images). Both extend from the FR into the frontal sinus &amp; cannot be differentiated on coronal CT.](cdc2b526-2166-472b-bf7b-bb7bac89e436)
*Coronal NECT in the same patient shows a right FBC (confirmed by right parasagittal CT images) &amp; a larger left type 3 Kuhn cell (confirmed by evaluating left parasagittal CT images). Both extend from the FR into the frontal sinus &amp; cannot be differentiated on coronal CT.*
![Left parasagittal bone NECT in the same patient shows a left type 3 Kuhn cell. On sagittal images, the posterosuperior wall of a type 3 Kuhn cell (anterior to the frontal sinus/recess) is a free partition in the FR &amp; frontal sinus with an air gap of the frontal sinus/recess between it &amp; the skull base.](ab06cd73-ef92-423f-a0ca-ef794d96de7a)
*Left parasagittal bone NECT in the same patient shows a left type 3 Kuhn cell. On sagittal images, the posterosuperior wall of a type 3 Kuhn cell (anterior to the frontal sinus/recess) is a free partition in the FR &amp; frontal sinus with an air gap of the frontal sinus/recess between it &amp; the skull base.*
### Coronal Bone CT
![The 1st of 3 coronal CT images presented from posterior to anterior shows the course of the anterior ethmoidal arteries that run in the &quot;anterior ethmoidal notch&quot; along the medial orbital wall, crossing anterior ethmoid cells in the anteromedial oblique bony canal called the &quot;anterior ethmoidal canal,&quot; &amp; then entering the anterior cranial fossa at a point in the lateral lamella of the cribriform plate (near its junction with fovea ethmoidalis) called the &quot;ethmoidal sulcus.&quot; The anterior ethmoidal canal is ~ 8 mm long with 40% showing some bony dehiscence &amp; lies ~ 11 mm (range: 6-15 mm) behind the posterior wall of the FR (in the suprabullar recess in 85%). It is usually in contact with the skull base (right side in this patient), but is sometimes 1-3 mm below the skull base within a bony mesentery (left side). The anterior ethmoidal artery usually lies well posterior to the anterior wall of the ethmoid bulla, so the &quot;intact bulla&quot; technique for FR surgery can protect it to some extent.](17e25313-1610-4b40-af00-ca8833ec5a0f)
*The 1st of 3 coronal CT images presented from posterior to anterior shows the course of the anterior ethmoidal arteries that run in the &quot;anterior ethmoidal notch&quot; along the medial orbital wall, crossing anterior ethmoid cells in the anteromedial oblique bony canal called the &quot;anterior ethmoidal canal,&quot; &amp; then entering the anterior cranial fossa at a point in the lateral lamella of the cribriform plate (near its junction with fovea ethmoidalis) called the &quot;ethmoidal sulcus.&quot; The anterior ethmoidal canal is ~ 8 mm long with 40% showing some bony dehiscence &amp; lies ~ 11 mm (range: 6-15 mm) behind the posterior wall of the FR (in the suprabullar recess in 85%). It is usually in contact with the skull base (right side in this patient), but is sometimes 1-3 mm below the skull base within a bony mesentery (left side). The anterior ethmoidal artery usually lies well posterior to the anterior wall of the ethmoid bulla, so the &quot;intact bulla&quot; technique for FR surgery can protect it to some extent.*
![The 2nd coronal CT shows the course of the anterior ethmoidal arteries.](4679a518-dcd5-4a9d-97bd-2fc2ebf927e9)
*The 2nd coronal CT shows the course of the anterior ethmoidal arteries.*
![The 3rd coronal CT shows the course of the anterior ethmoidal arteries.](87caf42b-93b5-4f3d-85f7-ceee440ecb8c)
*The 3rd coronal CT shows the course of the anterior ethmoidal arteries.*
### Axial, Sagittal, & Coronal Bone CT
![Axial CT images in the same patient show bilateral anterior ethmoidal notches &amp; canals containing anterior ethmoidal arteries.](02571fd0-984d-44c2-bf97-95a33436bd44)
*Axial CT images in the same patient show bilateral anterior ethmoidal notches &amp; canals containing anterior ethmoidal arteries.*
![Sagittal CT images in the same patient show the right anterior ethmoidal canal in contact with the skull base, &amp; the left canal hanging down a few millimeters below the skull base within a bony mesentery. The posterior ethmoidal artery lies ~ 10 mm posterior to the anterior ethmoidal artery.](988928c1-17b5-4d82-aa3a-d881f559fc70)
*Sagittal CT images in the same patient show the right anterior ethmoidal canal in contact with the skull base, &amp; the left canal hanging down a few millimeters below the skull base within a bony mesentery. The posterior ethmoidal artery lies ~ 10 mm posterior to the anterior ethmoidal artery.*
![Coronal bone NECT shows SOECs immediately above the anterior ethmoidal notch/canal/sulcus on the right; this predisposes anterior ethmoid artery injury at FESS. The anterior ethmoid artery is relatively safer in this patient on the left side without SOECs where the anterior ethmoidal notch/canal/sulcus abuts the fovea ethmoidalis/lateral lamella. SOECs can mimic a septated frontal sinus on coronal CT, but axial CT shows its location posterior to the frontal sinus, separated by a horizontally oriented septum. Note that the left frontal sinus septation is anteroposteriorly/obliquely oriented.](1f68cb62-b53e-46d3-9c27-cb113d793a9a)
*Coronal bone NECT shows SOECs immediately above the anterior ethmoidal notch/canal/sulcus on the right; this predisposes anterior ethmoid artery injury at FESS. The anterior ethmoid artery is relatively safer in this patient on the left side without SOECs where the anterior ethmoidal notch/canal/sulcus abuts the fovea ethmoidalis/lateral lamella. SOECs can mimic a septated frontal sinus on coronal CT, but axial CT shows its location posterior to the frontal sinus, separated by a horizontally oriented septum. Note that the left frontal sinus septation is anteroposteriorly/obliquely oriented.*
docs_md/articles/granular-cell-tumor_c086da8c-6213-4e2b-853b-422bad8c0013.md
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---
title: "Granular Cell Tumor"
docid: "c086da8c-6213-4e2b-853b-422bad8c0013"
authors:
- key: "8d5254e9-8dda-478b-8f08-bdee97a32c79"
value: "Karen L. Salzman, MD, FACR"
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lastUpdated: "08/21/25"
pageDescription: "Granular Cell Tumor"
pageKeywords: "Brain, Diagnosis, Anatomy-Based Diagnoses, Sella and Pituitary, Neoplasms, Granular Cell Tumor"
pageTitle: "Granular Cell Tumor | STATdx"
enhancedTitle: "Granular Cell Tumor"
type: "DX"
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breadcrumbs:
- "Brain"
- "Diagnosis"
- "Anatomy-Based Diagnoses"
- "Sella and Pituitary"
- "Neoplasms"
- "Granular Cell Tumor"
---
## KEY FACTS
- ### Terminology
- Neoplasms that arise from pituicytes, specialized glial cells of neurohypophysis or infundibulum
- Rare low-grade, nonendocrine neoplasms of sellar region
- Formerly called pituicytoma; granular cell tumor of neurohypophysis
- Part of 2021 WHO spectrum of thyroid transcription factor 1 (TTF-1) expressing pituitary tumors of posterior lobe
- ### Imaging
- Enhancing, well-circumscribed sellar/suprasellar or infundibular mass
- 1.5-6.0 cm
- CT: Sellar/suprasellar mass with hyperattenuation
- Rarely calcification may be present
- Best imaging tool: C+ MR with high-resolution imaging through sellar region
- Consider granular cell tumor if sellar/suprasellar mass appears separate from anterior pituitary gland
- ### Top Differential Diagnoses
- Pituitary macroadenoma
- Lymphocytic hypophysitis
- Pituicytoma
- Spindle cell oncocytoma
- Rathke cleft cyst
- ### Pathology
- WHO grade 1
- ### Clinical Issues
- Commonly asymptomatic (small lesions)
- Visual field deficit related to optic chiasm compression is most common presenting feature
- Less common symptoms: Panhypopituitarism, galactorrhea, amenorrhea, decreased libido, neuropsychological changes
- Typically present in adulthood, 5th-6th decades
- Generally benign clinical course
## TERMINOLOGY
- ### Abbreviations
- Granular cell tumor (GCT)
- ### Synonyms
- Formerly called pituicytoma; GCT of neurohypophysis
- ### Definitions
- Neoplasms that arise from pituicytes, specialized glia of neurohypophysis or infundibulum
- Rare low-grade, nonendocrine neoplasms of sellar region
- Part of 2021 WHO spectrum of thyroid transcription factor1 (TTF-1) expressing pituitary tumors of posterior lobe
## IMAGING
- ### General Features
- #### Best diagnostic clue
- Enhancing, well-circumscribed sellar/suprasellar or infundibular mass
- #### Location
- Sellar and suprasellar or infundibular mass
- Rare reports of anterior 3rd ventricle mass
- #### Size
- 1.5-6.0 cm
- #### Morphology
- Lobulated and well circumscribed
- ### CT Findings
- #### NECT
- Sellar/suprasellar mass with hyperattenuation
- Rarely calcification may be present
- ### MR Findings
- #### T1WI
- Sellar/suprasellar mass isointense to gray matter
- #### T1WI C+
- Enhancement may be homogeneous or heterogeneous
- ### Imaging Recommendations
- #### Best imaging tool
- C+ MR with high-resolution imaging through sellar region
## DIFFERENTIAL DIAGNOSIS
- [Pituitary Macroadenoma](/document/pituitary-microadenomapituitary-ne-/ff665ceb-8936-4259-84b0-7a568e53890f)
- Sellar and suprasellar enhancing mass
- Arises from adenohypophysis
- May be indistinguishable
- [Lymphocytic Hypophysitis](/document/lymphocytic-hypophysitis/747903f7-8aa7-424c-8c60-89f12e19aba2)
- May be indistinguishable from macroadenoma
- May present as infundibular mass
- Typically pregnant or postpartum females
- May be autoimmune, granulomatous, IgG4, or drug related
- [Pituicytoma](/document/pituicytoma/fe593d2b-aab5-4f7e-95b5-0f20e8df96c5)
- May be intrasellar or suprasellar mass
- May be separate from adenohypophysis
- [Spindle Cell Oncocytoma](/document/spindle-cell-oncocytoma/9d25f5c6-63d1-4050-a419-8e73945873a1)
- Imaging mimics macroadenoma
- Enhancing sellar and suprasellar mass
- May invade cavernous sinus
- [Rathke Cleft Cyst](/document/rathke-cleft-cyst/a5a3a735-ad86-4fd2-bcb8-2181c48ba3da)
- Nonenhancing cystic sellar &/or suprasellar lesion
- Intracystic nodule in up to 75%
## PATHOLOGY
- ### General Features
- #### Associated abnormalities
- GCTs have been found in associated with adenomas
- Small granular cell clusters have been found in up to 17% of autopsy series
- ### Staging, Grading, & Classification
- WHO grade 1
- ### Gross Pathologic & Surgical Features
- Lobulated, well-circumscribed mass, soft but rubbery
- More firm than pituitary adenoma
- ### Microscopic Features
- Densely packed polygonal cells with abundant granular eosinophilic cytoplasm
- Electron microscopy: Cytoplasm is filled with phagolysosomes containing electron-dense material and membranous debris
- Nuclear TTF1 expression; CD68 or α1-antitrypsin immunoreactivity
## CLINICAL ISSUES
- ### Presentation
- #### Most common signs/symptoms
- Commonly asymptomatic (small lesions)
- Visual field deficit related to optic chiasm compression
- #### Other signs/symptoms
- Panhypopituitarism, galactorrhea, amenorrhea, decreased libido, neuropsychological changes
- Rarely diabetes insipidus
- ### Demographics
- #### Age
- Typically present in adulthood, 5th-6th decades
- #### Gender
- F:M = 2:1
- ### Natural History & Prognosis
- Rare (~ 200 reported cases)
- Generally benign clinical course
- ### Treatment
- Surgical resection
## DIAGNOSTIC CHECKLIST
- ### Image Interpretation Pearls
- Consider GCT if sellar/suprasellar mass appears separate from anterior pituitary gland
f92d73fb-0c3a-497a-96e8-6e2a161fcfe0
## References
## Selected References
1. [Tomita T et al: Pituitary neuroendocrine tumors and granular cell pituicytomas at autopsy: Incidence, cell types, locations, and histogenesis in 150 pituitary glands. Am J Clin Pathol. 162(5):509-520, 2024](http://www.ncbi.nlm.nih.gov/pubmed/?term=38913876%5Bpmid%5D)
1. [Lopez G et al: Granular cell tumor of the neurohypophysis presenting as a third ventricle mass. Neuropathology. 43(6):472-8, 2023](http://www.ncbi.nlm.nih.gov/pubmed/?term=37147874%5Bpmid%5D)
1. [Schmid S et al: Genetic and epigenetic characterization of posterior pituitary tumors. Acta Neuropathol. 142(6):1025-43, 2021](http://www.ncbi.nlm.nih.gov/pubmed/?term=34661724%5Bpmid%5D)
1. WHO Classification of Tumours Editorial Board: Pituicytoma, granular cell tumour of the sellar region and spindle cell oncocytoma. In WHO Classification of Tumours: Central Nervous System Tumours. 5th ed. IARC Press, 2021
1. [Borg A et al: Tumors of the neurohypophysis: one unit's experience and literature review. World Neurosurg. 134:e968-78, 2020](http://www.ncbi.nlm.nih.gov/pubmed/?term=31734425%5Bpmid%5D)
1. [Guerrero-Pérez F et al: Posterior pituitary tumours: the spectrum of a unique entity. a clinical and histological study of a large case series. Endocrine. 63(1):36-43, 2019](http://www.ncbi.nlm.nih.gov/pubmed/?term=30276594%5Bpmid%5D)
1. [Guerrero-Pérez F et al: Posterior pituitary tumours: the spectrum of a unique entity. A clinical and histological study of a large case series. Endocrine. 63(1):36-43, 2019](http://www.ncbi.nlm.nih.gov/pubmed/?term=30276594%5Bpmid%5D)
1. [Shibuya M: Welcoming the new WHO classification of pituitary tumors 2017: revolution in TTF-1-positive posterior pituitary tumors. Brain Tumor Pathol. 35(2):62-70, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29500747%5Bpmid%5D)
1. [Ahmed AK et al: Extent of surgical resection and tumor size predicts prognosis in granular cell tumor of the sellar region. Acta Neurochir (Wien). 159(11):2209-16, 2017](http://www.ncbi.nlm.nih.gov/pubmed/?term=28948361%5Bpmid%5D)
1. [Jian F et al: Surgical biopsies in patients with central diabetes insipidus and thickened pituitary stalks. Endocrine. 47(1):325-35, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24532100%5Bpmid%5D)
1. [Shizukuishi T et al: Granular cell tumor of the neurohypophysis with optic tract edema. Jpn J Radiol. 32(3):179-82, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24414885%5Bpmid%5D)
1. [Mete O et al: Spindle cell oncocytomas and granular cell tumors of the pituitary are variants of pituicytoma. Am J Surg Pathol. 37(11):1694-9, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23887161%5Bpmid%5D)
1. [Saiegh L et al: Granular cell tumor of the neurohypophysis: case report and review of the literature. Neuro Endocrinol Lett. 34(5):331-8, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23922042%5Bpmid%5D)
1. [Covington MF et al: Pituicytoma, spindle cell oncocytoma, and granular cell tumor: clarification and meta-analysis of the world literature since 1893. AJNR Am J Neuroradiol. 32(11):2067-72, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=21960498%5Bpmid%5D)
1. [Mumert ML et al: Cystic granular cell tumor mimicking Rathke cleft cyst. J Neurosurg. 114(2):325-8, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=20509726%5Bpmid%5D)
1. [Menon G et al: Symptomatic granular cell tumour of the pituitary. Br J Neurosurg. 22(1):126-30, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=17952719%5Bpmid%5D)
1. Fuller GN et el: Granular cell tumour of the neurohypophysis In Louis, DN et el: WHO Classification of Tumors of the Central Nervous System. 4th ed. IARC. 241-2, 2007
## Images
### Selected Images
![Coronal T2 MR in a 41-year-old man who presented with visual symptoms shows a discrete hypointense suprasellar mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/>.](images/app.statdx.com_image_thumbnail_dd0f2dce-29f7-4b65-a4fd-b545dbe9ee6b_annotated_true_size_900_quality_90_89d5981afd2b87542c23afbde3ce5a02fbd8c493.jpg)
*Coronal T2 MR in a 41-year-old man who presented with visual symptoms shows a discrete hypointense suprasellar mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/>.*
![Coronal T2 MR in a 41-year-old man who presented with visual symptoms shows a discrete hypointense suprasellar mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/>.](images/app.statdx.com_image_thumbnail_dd0f2dce-29f7-4b65-a4fd-b545dbe9ee6b_size_174_quality_85_17155ad1202407c734dde09c6cfe4822cbf8d273.jpg)
*Coronal T2 MR in a 41-year-old man who presented with visual symptoms shows a discrete hypointense suprasellar mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/>.*
![Sagittal T1 C+ MR in the same patient shows the enhancing mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/> is separate from the pituitary gland <img src='img/arrows/WO.png' alt='white open arrow'/> but is inseparable from the infundibulum. Granular cell tumors are rare low-grade, nonendocrine neoplasms arising from the infundibulum or neurohypophysis. These tumors are part of the 2021 WHO spectrum of TTF-1 expressing pituitary tumors of the posterior lobe.](images/app.statdx.com_image_thumbnail_d43f8fe8-de48-46dc-97ed-6662d2b99a16_annotated_true_size_900_quality_90_dc2a70b828d010ffa4da7af7f4bbf3fc1dd794c8.jpg)
*Sagittal T1 C+ MR in the same patient shows the enhancing mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/> is separate from the pituitary gland <img src='img/arrows/WO.png' alt='white open arrow'/> but is inseparable from the infundibulum. Granular cell tumors are rare low-grade, nonendocrine neoplasms arising from the infundibulum or neurohypophysis. These tumors are part of the 2021 WHO spectrum of TTF-1 expressing pituitary tumors of the posterior lobe.*
![Sagittal T1 MR in a 31-year-old woman with headache and visual complaints shows a sellar and suprasellar mass <img src='img/arrows/WO.png' alt='white open arrow'/> with superior displacement of the optic chiasm <img src='img/arrows/WS.png' alt='white solid arrow'/>. There is a hyperintense focus <img src='img/arrows/CC.png' alt='cyan curved arrow'/> along the inferior aspect of the mass.](images/app.statdx.com_image_thumbnail_cdaa1057-f363-467d-95aa-4561403882e2_annotated_true_size_900_quality_90_dbd5132da622336ae0b77398b1f5c5a96095e065.jpg)
*Sagittal T1 MR in a 31-year-old woman with headache and visual complaints shows a sellar and suprasellar mass <img src='img/arrows/WO.png' alt='white open arrow'/> with superior displacement of the optic chiasm <img src='img/arrows/WS.png' alt='white solid arrow'/>. There is a hyperintense focus <img src='img/arrows/CC.png' alt='cyan curved arrow'/> along the inferior aspect of the mass.*
![Sagittal T1 C+ MR in the same patient shows peripheral enhancement <img src='img/arrows/WO.png' alt='white open arrow'/> of the mass. The region of T1 hyperintensity is also seen, resembling an intracystic nodule <img src='img/arrows/CC.png' alt='cyan curved arrow'/>, typically seen in a Rathke cleft cyst. Granular cell tumor of the neurohypophysis was diagnosed at resection.](images/app.statdx.com_image_thumbnail_068e9a77-6238-49e7-8d43-dca7f8b2f36d_annotated_true_size_900_quality_90_f904661caecd2e0ec27b92063a306c8287f9e755.jpg)
*Sagittal T1 C+ MR in the same patient shows peripheral enhancement <img src='img/arrows/WO.png' alt='white open arrow'/> of the mass. The region of T1 hyperintensity is also seen, resembling an intracystic nodule <img src='img/arrows/CC.png' alt='cyan curved arrow'/>, typically seen in a Rathke cleft cyst. Granular cell tumor of the neurohypophysis was diagnosed at resection.*
### Additional Images
![Sagittal T1 C+ MR shows an enhancing mass along the superior infundibulum and anterior 3rd ventricle <img src='img/arrows/CO.png' alt='cyan open arrow'/>. Granular cell tumor was diagnosed at resection.](images/app.statdx.com_image_thumbnail_19afcf2f-d15a-4927-8ca3-44d1f7e8f8b5_annotated_true_size_900_quality_90_6c341a9cd0422f0055fed911a281a4a939434131.jpg)
*Sagittal T1 C+ MR shows an enhancing mass along the superior infundibulum and anterior 3rd ventricle <img src='img/arrows/CO.png' alt='cyan open arrow'/>. Granular cell tumor was diagnosed at resection.*
![Coronal T1 C+ MR shows a large sellar and suprasellar enhancing mass contacting the left optic chiasm <img src='img/arrows/WO.png' alt='white open arrow'/>. Granular cell tumor was diagnosed at resection. Imaging mimics the much more common pituitary macroadenoma.](images/app.statdx.com_image_thumbnail_07fc6077-2d75-43f7-b1d0-c9eb3aa9dddf_annotated_true_size_900_quality_90_efa2178b40c9ab23f3f70de08b6f90eb03159c2d.jpg)
*Coronal T1 C+ MR shows a large sellar and suprasellar enhancing mass contacting the left optic chiasm <img src='img/arrows/WO.png' alt='white open arrow'/>. Granular cell tumor was diagnosed at resection. Imaging mimics the much more common pituitary macroadenoma.*
![Sagittal T1 C+ MR in a 65-year-old woman shows an enhancing suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/>.](images/app.statdx.com_image_thumbnail_3a178642-103e-4a0e-b398-2da90007f5fe_annotated_true_size_900_quality_90_15dab86045dc4eb7173096ffc515cb95ae62be11.jpg)
*Sagittal T1 C+ MR in a 65-year-old woman shows an enhancing suprasellar mass <img src='img/arrows/CO.png' alt='cyan open arrow'/>.*
![Coronal T1 C+ MR in the same patient shows the suprasellar enhancing mass <img src='img/arrows/CO.png' alt='cyan open arrow'/> contacting the optic chiasm <img src='img/arrows/WS.png' alt='white solid arrow'/>. Imaging mimics the much more common pituitary macroadenoma. Granular cell tumors are rare low-grade, nonendocrine neoplasms arising from the infundibulum or neurohypophysis. These tumors are part of the 2021 WHO spectrum of TTF-1 expressing pituitary tumors of the posterior lobe.](images/app.statdx.com_image_thumbnail_e8c6d82d-53b3-411a-b2e4-538882685541_annotated_true_size_900_quality_90_cd318899c806f53f294a7231c967343df77dc412.jpg)
*Coronal T1 C+ MR in the same patient shows the suprasellar enhancing mass <img src='img/arrows/CO.png' alt='cyan open arrow'/> contacting the optic chiasm <img src='img/arrows/WS.png' alt='white solid arrow'/>. Imaging mimics the much more common pituitary macroadenoma. Granular cell tumors are rare low-grade, nonendocrine neoplasms arising from the infundibulum or neurohypophysis. These tumors are part of the 2021 WHO spectrum of TTF-1 expressing pituitary tumors of the posterior lobe.*
![Sagittal CT in a 41-year-old man with visual symptoms show a large hyperattenuating suprasellar mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/>, separate from the pituitary gland <img src='img/arrows/WO.png' alt='white open arrow'/>. Granular cell tumor was diagnosed at resection. Differential considerations in this case would include pituitary macroadenoma, chordoid glioma, a rare glial neoplasm typically arising in the anterior 3rd ventricle, and lymphoma, given the high attenuation.](c66dedb5-d388-41f7-b466-18f3c53b7aa4)
*Sagittal CT in a 41-year-old man with visual symptoms show a large hyperattenuating suprasellar mass <img src='img/arrows/CS.png' alt='cyan solid arrow'/>, separate from the pituitary gland <img src='img/arrows/WO.png' alt='white open arrow'/>. Granular cell tumor was diagnosed at resection. Differential considerations in this case would include pituitary macroadenoma, chordoid glioma, a rare glial neoplasm typically arising in the anterior 3rd ventricle, and lymphoma, given the high attenuation.*
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