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---
title: "Cisterna Magna Mass"
docid: "047add0c-7e4f-40a0-9933-8d6fa00a24f7"
authors:
- key: "d19354f3-7ff2-495a-ad3f-064122e45602"
value: "Bernadette L. Koch, MD"
- key: "20008105-51da-4bbf-aba6-e8253b2d9c21"
value: "Daniel E. Meltzer, MD"
breadcrumbs:
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name: "Head and Neck"
slug: "head-and-neck"
treeNodeId: "ed24ed8c-5d57-4629-879b-447b82d2973d"
-
name: "Differential Diagnosis"
slug: "differential-diagnosis"
treeNodeId: "40d68862-8975-4dde-ac2b-ebc43ab0fb5c"
-
name: "CPA-IAC and Posterior Fossa"
slug: "cpa-iac-and-posterior-fossa"
treeNodeId: "c590eedb-4a3b-4158-a04f-ad880564c992"
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name: "Anatomically Based Differentials"
slug: "anatomically-based-differentials"
treeNodeId: "debfb06c-8656-4f5d-92c1-eaa468185d78"
-
name: "Cisterna Magna Mass"
slug: "cisterna-magna-mass"
treeNodeId: null
category: "Head and Neck"
documentVersionId: "86b48ea6-d9ea-428a-b5cb-32a58aaf84b2"
imageCount: 37
lastUpdated: "07/16/24"
pageDescription: "Cisterna Magna Mass"
pageKeywords: "Head and Neck, Differential Diagnosis, CPA-IAC and Posterior Fossa, Anatomically Based Differentials, Cisterna Magna Mass"
pageTitle: "Cisterna Magna Mass | STATdx"
enhancedTitle: "Cisterna Magna Mass"
type: "DDX"
references: true
breadcrumbs:
- "Head and Neck"
- "Differential Diagnosis"
- "CPA-IAC and Posterior Fossa"
- "Anatomically Based Differentials"
- "Cisterna Magna Mass"
---
# ESSENTIAL INFORMATION
- ## Key Differential Diagnosis Issues
- Cisterna magna (CM) between medulla (anterior), occiput (posterior) (a.k.a. cerebellomedullary cistern)
- Below/behind inferior vermis
- Large medullary cistern masses may extend laterally, posteriorly into CM
- Most common adult lesions are tonsillar associated
- Indirect (secondary effect on tonsil) > direct (lesion in tonsil)
- MR and clinical information helps DDx
- ## Helpful Clues for Common Diagnoses
- **Herniation Syndromes, Intracranial**
- Tonsillar herniation most often 2° to posterior fossa (PF) mass effect
- Tonsils pushed down into CM
- Peg-like configuration of tonsils
- Tonsil folia usually oriented horizontally → become vertically oriented when herniated
- 4th ventricle may obstruct → obstructive hydrocephalus
- **Chiari 1**
- Pointed cerebellar tonsils ≥ 5 mm below foramen magnum (FM)
- Crowded FM + effaced CSF
- ± brainstem compression
- ± retroflexed odontoid, horizontal clivus, scoliosis
- PF usually normal size
- Syrinx in 30-70%
- Treatment aim = restore normal CSF flow at FM
- **Chiari 2**
- Small PF → contents herniates inferiorly through FM and superiorly through widened incisura
- Cascade of tissue (vermis, not tonsil) herniates downward through FM
- Caudal brainstem herniation with cervicomedullary kink, tectal beaking, falx insufficiency
- ± ventriculomegaly, subependymal gray matter heterotopia, &/or polymicrogyria
- ~ 100% secondary to open spinal dysraphism, most often myelomeningocele
- **Dandy-Walker Continuum**
- Dandy-Walker continuum is broad spectrum of cystic PF malformations
- 2/3 have associated CNS &/or extracranial anomalies
- All may have inner table occipital bone scalloping
- Dandy-Walker malformation classic triad
- Vermian agenesis/hypogenesis
- Cystic dilatation 4th ventricle
- Large PF with lambdoid-torcular inversion
- ± hydrocephalus
- Vermian hypoplasia
- Varying degrees of vermian hypoplasia
- ± rotation of vermis
- No enlargement of PF
- Blake pouch cyst
- Open 4th ventricle
- Elevated tegmentovermian angle
- Normal size and morphology of vermis
- Mega CM
- Enlarged retrocerebellar cistern communicates with normal 4th ventricle
- Normal vermis
- ## Helpful Clues for Less Common Diagnoses
- **Arachnoid Cyst**
- Sharply demarcated extraaxial cyst that follows CSF attenuation/signal
- FLAIR suppresses; no diffusion restriction
- Size varies from few millimeters to giant
- Often asymptomatic, found incidentally
- Cerebellopontine angle (CPA) location > CM
- **Ependymoma**
- Anywhere in neuraxis: 2/3 in PF, 1/3 in supratentorial
- 3rd most common malignant pediatric brain tumor arising in PF
- Heterogeneous T1/T2 signal with mild to moderate enhancement
- Soft or "plastic" tumor squeezes out of 4th ventricle foramina into cisterns
- Calcification common (50%)
- ± cysts, hemorrhage
- Sagittal imaging can distinguish origin as floor vs. roof of 4th ventricle
- CSF seeding may occur → image entire neuraxis
- **Meningioma**
- CM rare PF location
- CPA, medullary cisterns more common than CM
- CM meningiomas usually arise from occipital squamosa
- Well-demarcated, lobulated/rounded enhancing mass with dural attachment
- Hyperostosis, tumoral calcifications, ↑ vascular markings
- **Metastasis**
- Linear or nodular meningeal enhancement
- MR CSF flow may be helpful establishing location and degree of CSF obstruction
- Primary tumors include breast, lung, melanoma, prostate
- Lymphoproliferative malignancy = lymphoma and leukemia
- Primary CNS tumor seed basal cisterns (drop metastases)
- **Image entire neuraxis**
- **Intracranial Hypotension**
- Sagittal shows brain descent in 40-50%
- Caudal displacement of cerebellar tonsils in 25-75%
- Diffusely and intensely enhancing dura in 85%
- Bilateral subdural fluid collections in 15%
- Dural venous sinus may be distended (convex margins)
- Enlarged pituitary
- Frequently misdiagnosed syndrome of headache caused by ↓ intracranial CSF pressure from spontaneous spinal CSF leak
- ## Helpful Clues for Rare Diagnoses
- **Subependymoma**
- T2-hyperintense lobular, nonenhancing intraventricular mass
- When arises from 4th ventricle floor, may extend posteroinferiorly into CM
- More common in middle-aged, older adults
- 0.7% of intracranial neoplasms
- **Epidermoid Cyst**
- Congenital inclusion cysts
- Lobulated, irregular, CSF-like mass with "fronds" insinuate cistern
- FLAIR usually does not completely null; diffusion yields high-signal restriction
- 0.2-1.8% of all primary intracranial tumors
- CPA cistern (40-50%) > 4th ventricle (17%) > sellar/parasellar (10-15%)
- Rare malignant degeneration into squamous cell carcinoma
- **Dermoid Cyst**
- Fat appearance: Use fat suppression sequence to confirm
- With rupture, fat droplets in cisterns, sulci, and ventricles with extensive MR enhancement possible from chemical meningitis
- Rare: < 0.5% of primary intracranial tumors
- Rupture can cause significant morbidity/mortality
- Rare malignant degeneration into squamous cell carcinoma
- **Hemangioblastoma**
- Intraaxial PF mass with cyst, enhancing mural nodule abutting pia
- Classified as 1 of mesenchymal, nonmeningothelial tumors
- Familial = von Hippel-Lindau
- ≈ 30% of patients with hemangioblastoma have von Hippel-Lindau
- 7-10% of PF tumors
- **Neurenteric Cyst**
- Round/lobulated, nonenhancing, slightly hyperintense to CSF mass
- Most intracranial NECs found in PF
- Benign malformative endodermal CNS cyst
- Part of split spinal cord malformation spectrum; persistent neurenteric canal
- Location
- Thoracic (42%), cervical (32%)
- Others: Lumbar spine, basilar cisterns, brain parenchyma
- Anterior medullary, CPA cisterns > CM
## References
# Selected References
1. [Pindrik J et al: Imaging in Chiari I malformation. Neurosurg Clin N Am. 34(1):67-79, 2023](http://www.ncbi.nlm.nih.gov/pubmed/?term=36424066%5Bpmid%5D)
1. [Paun L et al: Foramen magnum meningiomas: a systematic review and meta-analysis. Neurosurg Rev. 44(5):2583-96, 2021](http://www.ncbi.nlm.nih.gov/pubmed/?term=33507444%5Bpmid%5D)
1. [Menezes AH et al: Neurenteric cysts at foramen magnum in children: presentation, imaging characteristics, and surgical management-case series and literature review. Childs Nerv Syst. 36(7):1379-84, 2020](http://www.ncbi.nlm.nih.gov/pubmed/?term=32322975%5Bpmid%5D)
1. [Abdel Razek AA et al: Magnetic resonance imaging of malformations of midbrain-hindbrain. J Comput Assist Tomogr. 40(1):14-25, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=26599961%5Bpmid%5D)
1. [Dorfer C et al: Ependymoma: a heterogeneous tumor of uncertain origin and limited therapeutic options. Handb Clin Neurol. 134:417-31, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=26948369%5Bpmid%5D)
1. [Louis DN et al: The 2016 World Health Organization Classification of Tumors of the Central Nervous System: a summary. Acta Neuropathol. 131(6):803-20, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=27157931%5Bpmid%5D)
1. [Tao C et al: Prognostic factors affecting the surgical outcome of anterolateral benign tumors in the foramen magnum region. Int J Surg. 33 Pt A:172-6, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=27528437%5Bpmid%5D)
1. [Tian W et al: A quantitative study of intracranial hypotensive syndrome by magnetic resonance. Clin Neurol Neurosurg. 141:71-6, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=26745515%5Bpmid%5D)
1. [Yamahata H et al: Exploitation of simple classification and space created by the tumor for the treatment of foramen magnum meningiomas. World Neurosurg. 87:1-7, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=26409077%5Bpmid%5D)
1. [Cesmebasi A et al: The Chiari malformations: a review with emphasis on anatomical traits. Clin Anat. 28(2):184-94, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25065525%5Bpmid%5D)
1. [Liao CC et al: Clinical features and surgical outcomes of sporadic cerebellar hemangioblastomas. Clin Neurol Neurosurg. 125:160-5, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=25156409%5Bpmid%5D)
## Images
### Selected Images
![Sagittal T1 C+ MR shows a cystic mass with an enhancing nodule <img src='/img/arrows/WS.png'/>, consistent with hemangioblastoma, pushing the tonsils inferiorly through the foramen magnum <img src='/img/arrows/WO.png'/>. Note effaced 4th ventricle <img src='/img/arrows/WC.png'/>, enlarged foramen of Monro <img src='/img/arrows/CS.png'/>, and enlarged 3rd <img src='/img/arrows/CO.png'/> and lateral <img src='/img/arrows/CC.png'/> ventricles, consistent with obstructive hydrocephalus.](images/app.statdx.com_image_thumbnail_d93e03ab-ee6a-4de8-b332-8660df2448e1_annotated_true_size_900_quality_90_11e9ec7f.jpg)
**Herniation Syndromes, Intracranial**
*Sagittal T1 C+ MR shows a cystic mass with an enhancing nodule <img src='/img/arrows/WS.png'/>, consistent with hemangioblastoma, pushing the tonsils inferiorly through the foramen magnum <img src='/img/arrows/WO.png'/>. Note effaced 4th ventricle <img src='/img/arrows/WC.png'/>, enlarged foramen of Monro <img src='/img/arrows/CS.png'/>, and enlarged 3rd <img src='/img/arrows/CO.png'/> and lateral <img src='/img/arrows/CC.png'/> ventricles, consistent with obstructive hydrocephalus.*
![Sagittal T1 C+ MR shows a cystic mass with an enhancing nodule <img src='/img/arrows/WS.png'/>, consistent with hemangioblastoma, pushing the tonsils inferiorly through the foramen magnum <img src='/img/arrows/WO.png'/>. Note effaced 4th ventricle <img src='/img/arrows/WC.png'/>, enlarged foramen of Monro <img src='/img/arrows/CS.png'/>, and enlarged 3rd <img src='/img/arrows/CO.png'/> and lateral <img src='/img/arrows/CC.png'/> ventricles, consistent with obstructive hydrocephalus.](images/app.statdx.com_image_thumbnail_d93e03ab-ee6a-4de8-b332-8660df2448e1_size_174_quality_85_c6e99252.jpg)
**Herniation Syndromes, Intracranial**
*Sagittal T1 C+ MR shows a cystic mass with an enhancing nodule <img src='/img/arrows/WS.png'/>, consistent with hemangioblastoma, pushing the tonsils inferiorly through the foramen magnum <img src='/img/arrows/WO.png'/>. Note effaced 4th ventricle <img src='/img/arrows/WC.png'/>, enlarged foramen of Monro <img src='/img/arrows/CS.png'/>, and enlarged 3rd <img src='/img/arrows/CO.png'/> and lateral <img src='/img/arrows/CC.png'/> ventricles, consistent with obstructive hydrocephalus.*
![Sagittal T2 MR in a patient with occipital headaches shows a significantly pointed configuration of a low-lying cerebellar tonsil <img src='/img/arrows/WS.png'/> to the level of the midposterior ring of C2. Notice also the dorsally tilted dens <img src='/img/arrows/WO.png'/>, effacement of CSF at the foramen magnum, and associated cervicothoracic syrinx <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_f32667fd-ebff-4c5c-bd14-80a9c76d4c17_annotated_true_size_900_quality_90_0d739782.jpg)
**Chiari 1**
*Sagittal T2 MR in a patient with occipital headaches shows a significantly pointed configuration of a low-lying cerebellar tonsil <img src='/img/arrows/WS.png'/> to the level of the midposterior ring of C2. Notice also the dorsally tilted dens <img src='/img/arrows/WO.png'/>, effacement of CSF at the foramen magnum, and associated cervicothoracic syrinx <img src='/img/arrows/WC.png'/>.*
![Sagittal T2 MR shows a small posterior fossa with extension of the cerebellar peg <img src='/img/arrows/WS.png'/> through the foramen magnum to the level of C6. The cervicomedullary junction and 4th ventricle <img src='/img/arrows/WO.png'/> are low-lying and there is mild tectal beaking <img src='/img/arrows/WC.png'/> and moderate prominence of the massa intermedia <img src='/img/arrows/BS.png'/>.](images/app.statdx.com_image_thumbnail_3c1182ce-603f-414b-9ecd-728488f8ea13_annotated_true_size_900_quality_90_73ce0e43.jpg)
**Chiari 2**
*Sagittal T2 MR shows a small posterior fossa with extension of the cerebellar peg <img src='/img/arrows/WS.png'/> through the foramen magnum to the level of C6. The cervicomedullary junction and 4th ventricle <img src='/img/arrows/WO.png'/> are low-lying and there is mild tectal beaking <img src='/img/arrows/WC.png'/> and moderate prominence of the massa intermedia <img src='/img/arrows/BS.png'/>.*
![Sagittal T2 MR demonstrates a markedly enlarged posterior fossa with cystic dilatation of the 4th ventricle <img src='/img/arrows/WS.png'/>, upward rotation of severely hypoplastic vermis <img src='/img/arrows/WO.png'/>, markedly enlarged posterior fossa, and elevated torcula.](images/app.statdx.com_image_thumbnail_0c6467dd-b795-4546-9afd-1680b2372865_annotated_true_size_900_quality_90_45a0b4c2.jpg)
**Dandy-Walker Continuum**
*Sagittal T2 MR demonstrates a markedly enlarged posterior fossa with cystic dilatation of the 4th ventricle <img src='/img/arrows/WS.png'/>, upward rotation of severely hypoplastic vermis <img src='/img/arrows/WO.png'/>, markedly enlarged posterior fossa, and elevated torcula.*
![Sagittal T1WI MR shows a CSF isointense arachnoid cyst <img src='/img/arrows/WO.png'/> filling the lower posterior fossa, effacing the cisterna magna, flattening the cervicomedullary junction <img src='/img/arrows/WS.png'/>, and extending caudally into the upper cervical canal.](images/app.statdx.com_image_thumbnail_9358bfe0-0e81-45e5-a915-382de4ca45a8_annotated_true_size_900_quality_90_5ee2bea0.jpg)
**Arachnoid Cyst**
*Sagittal T1WI MR shows a CSF isointense arachnoid cyst <img src='/img/arrows/WO.png'/> filling the lower posterior fossa, effacing the cisterna magna, flattening the cervicomedullary junction <img src='/img/arrows/WS.png'/>, and extending caudally into the upper cervical canal.*
![Sagittal T1WI C+ MR shows enhancing tissue extruding through the foramen of Magendie, filling the cisterna magna <img src='/img/arrows/WS.png'/>. Resultant obstruction has caused enlargement of the cerebral aqueduct <img src='/img/arrows/WC.png'/> and dilated 3rd ventricle <img src='/img/arrows/WO.png'/>.](images/app.statdx.com_image_thumbnail_dcf88032-90a4-4cdc-837d-0db68076ba0d_annotated_true_size_900_quality_90_8996372c.jpg)
**Ependymoma**
*Sagittal T1WI C+ MR shows enhancing tissue extruding through the foramen of Magendie, filling the cisterna magna <img src='/img/arrows/WS.png'/>. Resultant obstruction has caused enlargement of the cerebral aqueduct <img src='/img/arrows/WC.png'/> and dilated 3rd ventricle <img src='/img/arrows/WO.png'/>.*
![Sagittal T1WI MR demonstrates dural-based tumor <img src='/img/arrows/WS.png'/> with significant mass effect compressing and displacing the cerebellum. Note the trapped CSF clefts <img src='/img/arrows/WC.png'/>. The tumor encroaches on the cisterna magna.](images/app.statdx.com_image_thumbnail_552dcc86-9bc3-45d4-a79b-5f70d7aee358_annotated_true_size_900_quality_90_b1b07faa.jpg)
**Meningioma**
*Sagittal T1WI MR demonstrates dural-based tumor <img src='/img/arrows/WS.png'/> with significant mass effect compressing and displacing the cerebellum. Note the trapped CSF clefts <img src='/img/arrows/WC.png'/>. The tumor encroaches on the cisterna magna.*
![Axial T1WI C+ MR shows a typical case of primary CNS lymphoma with subependymal tumor spread. Note a posterior fossa mass near the foramen of Luschka <img src='/img/arrows/WS.png'/> as well as a 2nd dural-based mass <img src='/img/arrows/WO.png'/>.](images/app.statdx.com_image_thumbnail_78b4e7b9-3149-4afa-8312-4f8ac2681b52_annotated_true_size_900_quality_90_f84a81af.jpg)
**Metastasis**
*Axial T1WI C+ MR shows a typical case of primary CNS lymphoma with subependymal tumor spread. Note a posterior fossa mass near the foramen of Luschka <img src='/img/arrows/WS.png'/> as well as a 2nd dural-based mass <img src='/img/arrows/WO.png'/>.*
![Sagittal T1WI C+ MR shows obliteration of the suprasellar cistern <img src='/img/arrows/WS.png'/>, sagging/fat midbrain with closed angle between the peduncles and the pons <img src='/img/arrows/WO.png'/>, dural enhancement <img src='/img/arrows/WC.png'/>, and tonsillar descent <img src='/img/arrows/BO.png'/> with effacement of the cisterna magna.](images/app.statdx.com_image_thumbnail_43f42495-6e64-47ac-8abd-7ca9ca2ff540_annotated_true_size_900_quality_90_a13877a5.jpg)
**Intracranial Hypotension**
*Sagittal T1WI C+ MR shows obliteration of the suprasellar cistern <img src='/img/arrows/WS.png'/>, sagging/fat midbrain with closed angle between the peduncles and the pons <img src='/img/arrows/WO.png'/>, dural enhancement <img src='/img/arrows/WC.png'/>, and tonsillar descent <img src='/img/arrows/BO.png'/> with effacement of the cisterna magna.*
![Sagittal T1WI C+ MR in 40-year-old man shows an enhancing mass at the bottom of the 4th ventricle <img src='/img/arrows/WS.png'/> filling the cisterna magna.](images/app.statdx.com_image_thumbnail_7a028d65-ddd4-458e-9bb8-cd91406e17cc_annotated_true_size_900_quality_90_a4e2aff3.jpg)
**Subependymoma**
*Sagittal T1WI C+ MR in 40-year-old man shows an enhancing mass at the bottom of the 4th ventricle <img src='/img/arrows/WS.png'/> filling the cisterna magna.*
![Sagittal T1WI MR shows a typical case of a large 4th ventricular epidermoid cyst <img src='/img/arrows/WS.png'/>, which follows CSF intensity but is often slightly brighter and mildly heterogeneous in signal.](images/app.statdx.com_image_thumbnail_ae931e3a-ee28-4c7d-854c-665d58b34439_annotated_true_size_900_quality_90_8f1340e9.jpg)
**Epidermoid Cyst**
*Sagittal T1WI MR shows a typical case of a large 4th ventricular epidermoid cyst <img src='/img/arrows/WS.png'/>, which follows CSF intensity but is often slightly brighter and mildly heterogeneous in signal.*
![Axial T2WI MR demonstrates a T2- hyperintense mass <img src='/img/arrows/WS.png'/> encroaching laterally upon the ventral CSF at the foramen magnum. There was evidence of rupture (not shown) causing recurrent meningitis.](images/app.statdx.com_image_thumbnail_fc461ab0-6909-4db8-b585-ee6b0495e584_annotated_true_size_900_quality_90_ab4bf44b.jpg)
**Dermoid Cyst**
*Axial T2WI MR demonstrates a T2- hyperintense mass <img src='/img/arrows/WS.png'/> encroaching laterally upon the ventral CSF at the foramen magnum. There was evidence of rupture (not shown) causing recurrent meningitis.*
![Sagittal T1WI C+ MR shows an enhancing vermian mass protruding through the foramen magnum <img src='/img/arrows/WS.png'/>. An associated cyst <img src='/img/arrows/WO.png'/> is deforming the 4th ventricle <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_b01e6fff-9cce-4843-8749-c18dfa0f8c59_annotated_true_size_900_quality_90_36cd9838.jpg)
**Hemangioblastoma**
*Sagittal T1WI C+ MR shows an enhancing vermian mass protruding through the foramen magnum <img src='/img/arrows/WS.png'/>. An associated cyst <img src='/img/arrows/WO.png'/> is deforming the 4th ventricle <img src='/img/arrows/WC.png'/>.*
![Axial T1WI C+ MR shows a neurenteric cyst encroaching <img src='/img/arrows/BS.png'/> upon the prepontine cistern. Although most often these are located anteriorly, they may arise posteriorly at the cisterna magnum.](images/app.statdx.com_image_thumbnail_baa88901-5c32-4263-95c8-65e0655116f4_annotated_true_size_900_quality_90_4bc83322.jpg)
**Neurenteric Cyst**
*Axial T1WI C+ MR shows a neurenteric cyst encroaching <img src='/img/arrows/BS.png'/> upon the prepontine cistern. Although most often these are located anteriorly, they may arise posteriorly at the cisterna magnum.*
### Additional Images
![Sagittal T1WI MR shows a small posterior fossa with extension of the cerebellar peg <img src='/img/arrows/WS.png'/> through the foramen magnum to the level of C3. The cervicomedullary junction and 4th ventricle <img src='/img/arrows/WO.png'/> are low-lying, and there is tectal beaking <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_f0e743d3-48ed-4542-b207-11bb55f9d934_annotated_true_size_900_quality_90_a2144ce8.jpg)
**Chiari 2**
*Sagittal T1WI MR shows a small posterior fossa with extension of the cerebellar peg <img src='/img/arrows/WS.png'/> through the foramen magnum to the level of C3. The cervicomedullary junction and 4th ventricle <img src='/img/arrows/WO.png'/> are low-lying, and there is tectal beaking <img src='/img/arrows/WC.png'/>.*
![Sagittal T1WI MR demonstrates a markedly enlarged posterior fossa with cystic dilatation of the 4th ventricle <img src='/img/arrows/WO.png'/>, upwardly rotated hypoplastic vermis <img src='/img/arrows/WS.png'/>, and low-lying torcular Herophili <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_597739b9-7ca6-42c3-9220-6e8459aded8e_annotated_true_size_900_quality_90_271d003d.jpg)
**Dandy-Walker Continuum**
*Sagittal T1WI MR demonstrates a markedly enlarged posterior fossa with cystic dilatation of the 4th ventricle <img src='/img/arrows/WO.png'/>, upwardly rotated hypoplastic vermis <img src='/img/arrows/WS.png'/>, and low-lying torcular Herophili <img src='/img/arrows/WC.png'/>.*
![Sagittal T2 MR in a patient with occipital headaches shows a significantly pointed configuration of a low-lying cerebellar tonsil <img src='/img/arrows/WS.png'/> to the level of the midposterior ring of C2. Notice also the dorsally tilted dens <img src='/img/arrows/WO.png'/> and effacement of CSF at the foramen magnum.](images/app.statdx.com_image_thumbnail_dac4c49b-c2b5-416f-a085-f7b7e6de8e51_annotated_true_size_900_quality_90_60d55480.jpg)
**Chiari 1**
*Sagittal T2 MR in a patient with occipital headaches shows a significantly pointed configuration of a low-lying cerebellar tonsil <img src='/img/arrows/WS.png'/> to the level of the midposterior ring of C2. Notice also the dorsally tilted dens <img src='/img/arrows/WO.png'/> and effacement of CSF at the foramen magnum.*
![Sagittal T1WI MR shows inferior extension of the peg-like cerebellar tonsils <img src='/img/arrows/WS.png'/> well below the level of the foramen magnum <img src='/img/arrows/BO.png'/>, consistent with Chiari 1.](images/app.statdx.com_image_thumbnail_bf765af5-15a4-473e-8df5-a11a991e90bc_annotated_true_size_900_quality_90_1e09c50d.jpg)
**Chiari 1**
*Sagittal T1WI MR shows inferior extension of the peg-like cerebellar tonsils <img src='/img/arrows/WS.png'/> well below the level of the foramen magnum <img src='/img/arrows/BO.png'/>, consistent with Chiari 1.*
![Axial T2WI MR at the level of the foramen magnum demonstrates downward tonsillar herniation <img src='/img/arrows/WS.png'/> secondary to mass affect from brain death.](images/app.statdx.com_image_thumbnail_4ec0f703-c702-49e8-a1ed-adb06f9da9c5_annotated_true_size_900_quality_90_813870b0.jpg)
**Herniation Syndromes, Intracranial**
*Axial T2WI MR at the level of the foramen magnum demonstrates downward tonsillar herniation <img src='/img/arrows/WS.png'/> secondary to mass affect from brain death.*
![Sagittal T1WI MR shows cerebellar tonsillar herniation <img src='/img/arrows/WC.png'/> from a large left posterior fossa mass. Note compression of 4th ventricle <img src='/img/arrows/WO.png'/>. Supratentorial ventricles are enlarged <img src='/img/arrows/WS.png'/>.](images/app.statdx.com_image_thumbnail_8aaa21ec-1c19-4e6c-8181-592b3df7869d_annotated_true_size_900_quality_90_60eba5bd.jpg)
**Herniation Syndromes, Intracranial**
*Sagittal T1WI MR shows cerebellar tonsillar herniation <img src='/img/arrows/WC.png'/> from a large left posterior fossa mass. Note compression of 4th ventricle <img src='/img/arrows/WO.png'/>. Supratentorial ventricles are enlarged <img src='/img/arrows/WS.png'/>.*
![Sagittal CINE phase-contrast CSF flow - diastolic shows diminished posterior CSF flow <img src='/img/arrows/WS.png'/> compared to anterior CSF flow <img src='/img/arrows/BO.png'/> at the site of tonsillar impaction.](images/app.statdx.com_image_thumbnail_bbdce702-8985-4ec6-a3e4-cad6dea34ada_annotated_true_size_900_quality_90_9fd2b7f0.jpg)
**Chiari 1**
*Sagittal CINE phase-contrast CSF flow - diastolic shows diminished posterior CSF flow <img src='/img/arrows/WS.png'/> compared to anterior CSF flow <img src='/img/arrows/BO.png'/> at the site of tonsillar impaction.*
![Sagittal T2WI MR shows a classic case of Chiari 1 with pointed cerebellar tonsils <img src='/img/arrows/WO.png'/> protruding through the foramen magnum and effacing the cisterna magna.](images/app.statdx.com_image_thumbnail_6840be04-8ddf-44dd-90f5-533d79cc1e88_annotated_true_size_900_quality_90_19b200f9.jpg)
**Chiari 1**
*Sagittal T2WI MR shows a classic case of Chiari 1 with pointed cerebellar tonsils <img src='/img/arrows/WO.png'/> protruding through the foramen magnum and effacing the cisterna magna.*
![Sagittal T2WI MR shows a small posterior fossa with caudal descent of cerebellar tonsillar tissue <img src='/img/arrows/WS.png'/>, elongation of the 4th ventricle <img src='/img/arrows/WC.png'/>, and cervical cord syrinx <img src='/img/arrows/WO.png'/>.](images/app.statdx.com_image_thumbnail_e8e875a9-dab9-4138-acad-70e88f4e90d9_annotated_true_size_900_quality_90_95de6bef.jpg)
**Chiari 2**
*Sagittal T2WI MR shows a small posterior fossa with caudal descent of cerebellar tonsillar tissue <img src='/img/arrows/WS.png'/>, elongation of the 4th ventricle <img src='/img/arrows/WC.png'/>, and cervical cord syrinx <img src='/img/arrows/WO.png'/>.*
![Axial FSPGR image demonstrates caudally displaced cerebellar tissue <img src='/img/arrows/WO.png'/> wrapping around the brainstem. This is sometimes referred to as a &quot;creeping cerebellum&quot; due to a small posterior fossa.](images/app.statdx.com_image_thumbnail_2881fed2-4a1d-4e08-8032-ccc2e2135a6c_annotated_true_size_900_quality_90_b9efe583.jpg)
**Chiari 2**
*Axial FSPGR image demonstrates caudally displaced cerebellar tissue <img src='/img/arrows/WO.png'/> wrapping around the brainstem. This is sometimes referred to as a &quot;creeping cerebellum&quot; due to a small posterior fossa.*
![Sagittal T1WI MR shows caudal descent of cerebellar vermian tissue <img src='/img/arrows/WS.png'/> and elongated 4th ventricle <img src='/img/arrows/WC.png'/> as well as callosal dysgenesis <img src='/img/arrows/WO.png'/> and a small posterior fossa.](images/app.statdx.com_image_thumbnail_5a4e9906-ab96-4d21-9cab-e237c76a221e_annotated_true_size_900_quality_90_77c3db2e.jpg)
**Chiari 2**
*Sagittal T1WI MR shows caudal descent of cerebellar vermian tissue <img src='/img/arrows/WS.png'/> and elongated 4th ventricle <img src='/img/arrows/WC.png'/> as well as callosal dysgenesis <img src='/img/arrows/WO.png'/> and a small posterior fossa.*
![Sagittal T1 C+ MR shows a small posterior fossa with extension of the vermis through the foramen magnum to the level of C1/2 <img src='/img/arrows/WS.png'/>. The 4th ventricle is small <img src='/img/arrows/WO.png'/>, and there is tectal beaking <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_fc43bc05-4fc8-45c2-8329-13bc355cf93c_annotated_true_size_900_quality_90_7e196aa3.jpg)
**Chiari 2**
*Sagittal T1 C+ MR shows a small posterior fossa with extension of the vermis through the foramen magnum to the level of C1/2 <img src='/img/arrows/WS.png'/>. The 4th ventricle is small <img src='/img/arrows/WO.png'/>, and there is tectal beaking <img src='/img/arrows/WC.png'/>.*
![Axial T2WI MR shows a normal 4th ventricle and vermis; however, there is a prominent retrocerebellar CSF space <img src='/img/arrows/WO.png'/>, which does not cause compression but does remodel endosteum, leading to mega cisterna magna.](images/app.statdx.com_image_thumbnail_c3afc83f-66c2-4438-9441-88dc439e4880_annotated_true_size_900_quality_90_bae05a32.jpg)
**Dandy-Walker Continuum**
*Axial T2WI MR shows a normal 4th ventricle and vermis; however, there is a prominent retrocerebellar CSF space <img src='/img/arrows/WO.png'/>, which does not cause compression but does remodel endosteum, leading to mega cisterna magna.*
![Sagittal T1WI MR demonstrates a CSF-intensity arachnoid cyst remodeling the endosteum <img src='/img/arrows/WS.png'/> and filling the cisterna magna <img src='/img/arrows/WO.png'/>.](images/app.statdx.com_image_thumbnail_91da2980-fb4a-4a4e-b638-7747bec7db0c_annotated_true_size_900_quality_90_eae82879.jpg)
**Arachnoid Cyst**
*Sagittal T1WI MR demonstrates a CSF-intensity arachnoid cyst remodeling the endosteum <img src='/img/arrows/WS.png'/> and filling the cisterna magna <img src='/img/arrows/WO.png'/>.*
![Sagittal T2WI MR shows heterogeneous features of an ependymoma. Focal hyperintense regions correspond to focal necrosis <img src='/img/arrows/WS.png'/> and hypointense regions correlate to calcification <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_f38e8e00-56df-4d69-b748-773ed89d905f_annotated_true_size_900_quality_90_69f8cdb4.jpg)
**Ependymoma**
*Sagittal T2WI MR shows heterogeneous features of an ependymoma. Focal hyperintense regions correspond to focal necrosis <img src='/img/arrows/WS.png'/> and hypointense regions correlate to calcification <img src='/img/arrows/WC.png'/>.*
![Axial T1 C+ MR demonstrates a heterogeneously enhancing ependymoma <img src='/img/arrows/BS.png'/> containing cystic elements <img src='/img/arrows/WO.png'/>.](images/app.statdx.com_image_thumbnail_8c0d32d7-f882-4d35-b39d-0cebc442af46_annotated_true_size_900_quality_90_21ba0570.jpg)
**Ependymoma**
*Axial T1 C+ MR demonstrates a heterogeneously enhancing ependymoma <img src='/img/arrows/BS.png'/> containing cystic elements <img src='/img/arrows/WO.png'/>.*
![Sagittal T1 C+ MR shows an enhancing mass expanding the 4th ventricle <img src='/img/arrows/WS.png'/>. The mass is also distending the obex <img src='/img/arrows/WO.png'/> and protruding through the foramen of Magendie into the cisterna magna <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_5fc91f03-53aa-4f1a-b923-2461c8433360_annotated_true_size_900_quality_90_de5dd820.jpg)
**Ependymoma**
*Sagittal T1 C+ MR shows an enhancing mass expanding the 4th ventricle <img src='/img/arrows/WS.png'/>. The mass is also distending the obex <img src='/img/arrows/WO.png'/> and protruding through the foramen of Magendie into the cisterna magna <img src='/img/arrows/WC.png'/>.*
![Axial T2WI MR demonstrates a posterior fossa meningioma <img src='/img/arrows/WS.png'/> with significant mass effect upon the cerebellum with interposed trapped CSF clefts <img src='/img/arrows/WO.png'/> and vessels <img src='/img/arrows/WC.png'/>.](images/app.statdx.com_image_thumbnail_d1c5e3a5-bf64-4a37-a40b-bb3a99f607ef_annotated_true_size_900_quality_90_329c2b60.jpg)
**Meningioma**
*Axial T2WI MR demonstrates a posterior fossa meningioma <img src='/img/arrows/WS.png'/> with significant mass effect upon the cerebellum with interposed trapped CSF clefts <img src='/img/arrows/WO.png'/> and vessels <img src='/img/arrows/WC.png'/>.*
![Axial T1 C+ MR of a meningioma shows an avidly enhancing, dural-based mass splaying the cerebellar hemispheres, flattening the 4th ventricle <img src='/img/arrows/WC.png'/>, with dural tail <img src='/img/arrows/WO.png'/>.](images/app.statdx.com_image_thumbnail_c7247000-384b-463a-ac68-4cfddc8bc020_annotated_true_size_900_quality_90_c30a12c4.jpg)
**Meningioma**
*Axial T1 C+ MR of a meningioma shows an avidly enhancing, dural-based mass splaying the cerebellar hemispheres, flattening the 4th ventricle <img src='/img/arrows/WC.png'/>, with dural tail <img src='/img/arrows/WO.png'/>.*
![Coronal T1 C+ MR demonstrates the diffuse enhancement of meningeal carcinomatosis from metastatic xanthoastrocytoma <img src='/img/arrows/WS.png'/> spread throughout the posterior fossa, folia, and also more cephalad.](images/app.statdx.com_image_thumbnail_1cdce1bc-69d9-42bf-b62f-e5bb173bebec_annotated_true_size_900_quality_90_eb210c6e.jpg)
**Metastasis**
*Coronal T1 C+ MR demonstrates the diffuse enhancement of meningeal carcinomatosis from metastatic xanthoastrocytoma <img src='/img/arrows/WS.png'/> spread throughout the posterior fossa, folia, and also more cephalad.*
![Sagittal T1WI MR shows tonsillar descent <img src='/img/arrows/WC.png'/> and dural thickening <img src='/img/arrows/WS.png'/> secondary to intracranial hypotension.](images/app.statdx.com_image_thumbnail_275e1525-c39f-4a67-a0c6-85527fff9775_annotated_true_size_900_quality_90_2634400b.jpg)
**Intracranial Hypotension**
*Sagittal T1WI MR shows tonsillar descent <img src='/img/arrows/WC.png'/> and dural thickening <img src='/img/arrows/WS.png'/> secondary to intracranial hypotension.*
![Axial DWI MR shows a hyperintense mass <img src='/img/arrows/WS.png'/> in the midline posterior fossa.](images/app.statdx.com_image_thumbnail_34b283f3-4ea9-4e5a-9cb3-881ab4f80a29_annotated_true_size_900_quality_90_5cf04a76.jpg)
**Epidermoid Cyst**
*Axial DWI MR shows a hyperintense mass <img src='/img/arrows/WS.png'/> in the midline posterior fossa.*
![Sagittal T1 C+ MR demonstrates a mostly solid hemangioblastoma <img src='/img/arrows/WS.png'/> involving the cerebellar tonsils and effacing the cisterna magna.](images/app.statdx.com_image_thumbnail_1be0b435-f039-412e-b180-4268d6bd5c32_annotated_true_size_900_quality_90_9f29c937.jpg)
**Hemangioblastoma**
*Sagittal T1 C+ MR demonstrates a mostly solid hemangioblastoma <img src='/img/arrows/WS.png'/> involving the cerebellar tonsils and effacing the cisterna magna.*