statdx/docs_md/articles/epidermoid-cyst_704c5ddf-e1f7-4a5d-a1b8-5b0e603170d9.md

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Epidermoid Cyst	704c5ddf-e1f7-4a5d-a1b8-5b0e603170d9	key value 5cff4116-3654-4b3a-bb75-5ebe0b8c9850 Anne G. Osborn, MD, FACR	name slug treeNodeId Brain brain 6d8829f1-14d7-45af-8675-255189aa526a name slug treeNodeId Diagnosis diagnosis 51c00394-446e-4a38-94af-d3b1d14d34e8 name slug treeNodeId Pathology-Based Diagnoses pathology-based-diagnoses d9d3a8ed-f21b-4831-8c77-591a3500ef77 name slug treeNodeId Primary Nonneoplastic Cysts primary-nonneoplastic-cysts 8037bffe-f61e-4433-b841-a263bcfbe056 name slug treeNodeId Epidermoid Cyst epidermoid-cyst null	Brain	4092685b-a22f-42ca-b14b-6a21122b651f	22	06/12/20	Epidermoid Cyst	Brain, Diagnosis, Pathology-Based Diagnoses, Primary Nonneoplastic Cysts, Epidermoid Cyst	Epidermoid Cyst | STATdx	Epidermoid Cyst	DX	true	Brain Diagnosis Pathology-Based Diagnoses Primary Nonneoplastic Cysts Epidermoid Cyst

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title: "Epidermoid Cyst" docid: "704c5ddf-e1f7-4a5d-a1b8-5b0e603170d9" authors:

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• name: "Epidermoid Cyst" slug: "epidermoid-cyst" treeNodeId: null category: "Brain" documentVersionId: "4092685b-a22f-42ca-b14b-6a21122b651f" imageCount: 22 lastUpdated: "06/12/20" pageDescription: "Epidermoid Cyst" pageKeywords: "Brain, Diagnosis, Pathology-Based Diagnoses, Primary Nonneoplastic Cysts, Epidermoid Cyst" pageTitle: "Epidermoid Cyst | STATdx" enhancedTitle: "Epidermoid Cyst" type: "DX" references: true breadcrumbs:
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---

KEY FACTS

• Terminology

  • Intracranial epidermoids ("pearly" tumor) - Congenital ectodermal inclusion cysts, not true neoplasm

• Imaging

  • CSF-like mass that insinuates cisterns and encases neurovascular structures
  • Morphology: Lobulated, irregular, cauliflower-like mass with "fronds"
  • FLAIR: Usually does not completely null
  • DWI: Diffusion restriction definitively distinguishes from arachnoid cyst

• Top Differential Diagnoses

  • Arachnoid cyst
  • Inflammatory cyst (i.e., neurocysticercosis)
  • Cystic neoplasm
  • Dermoid cyst

• Pathology

  • Arise from ectodermal inclusions during neural tube closure, 3rd to 5th week of embryogenesis

• Clinical Issues

  • Symptoms depend on location and effect on adjacent neurovascular structures - Most common symptom: Headache - Cranial nerves V, VII, VIII neuropathy common
  • 0.2-1.8% of all primary intracranial tumors
  • Rare malignant degeneration into squamous cell carcinoma
  • Treatment: Microsurgical resection - Recurrence common if incompletely removed

• Diagnostic Checklist

  • Insinuates CSF spaces, surrounds arteries, CNs with minimal displacement
  • Incomplete nulling on FLAIR; DWI hyperintense

TERMINOLOGY

• Synonyms

  • Ectodermal inclusion cyst
  • "Pearly" tumor

• Definitions

  • Intracranial epidermoids are congenital inclusion cysts (not "tumors")
  • Benign, slow-growing congenital lesions derived from ectodermal remnants sequestrated during embryogenesis

IMAGING

• General Features

  • Best diagnostic clue

    - CSF-like mass that insinuates cisterns and encases neurovascular structures
    

  • Location

    - Intradural (90%), strong predilection for basal cisterns
            - Cerebellopontine angle (CPA) (40-50%)
            - 4th ventricle (17%)
            - Parasellar/middle cranial fossa/sylvian fissure (10-15%)
            - Parenchymal (i.e., cerebral hemispheres) rare (1.5%)
            - Brainstem exceedingly rare
    - Extradural (10%)
            - Skull (intradiploic within frontal, parietal, occipital, sphenoid skull) as well as spine
    

  • Size

    - Variable; extradural intradiploic variants can become huge with minimal/no neurologic deficits
    - Grow slowly by desquamation of normal cells into cystic cavity
    

  • Morphology

    - Lobulated, irregular, cauliflower-like excrescences
    - Insinuates without mass effect unless large
    

• Radiographic Findings

  • Radiography

    - Diploic space epidermoids
            - May alter scalp, outer/inner skull tables, and epidural space appearance
            - Typically round or lobulated
            - Well delineated with sclerotic rim
    

• CT Findings

  • NECT

    - Round/lobulated mass
    - > 95% hypodense, resembling CSF
    - 10-25% contain calcifications
    - Rare variant = "dense" epidermoid
            - 3% of intracranial epidermoids
            - Secondary to hemorrhage, high protein, saponification of cyst debris to calcium soaps or iron-containing pigment
    

  • CECT

    - Usually none, though margin of cyst may show minimal enhancement
    

  • Bone CT

    - May have bony erosion; sharply corticated margins when intradiploic
    

• MR Findings

  • T1WI

    - Often (~ 75%) slightly hyperintense to CSF
    - Lobulated periphery may be slightly more hyperintense than center
    - Uncommonly hyperintense to brain ("white epidermoid") due to high triglycerides and unsaturated fatty acids
    - Uncommonly hypointense to CSF ("black epidermoid")
            - Presence of solid crystal cholesterol and keratin
            - Lack of triglycerides and unsaturated fatty acids
    

  • T2WI

    - Often isointense (65%) to slightly hyperintense (35%) to CSF
    - Very rarely hypointense due to calcification, ↓ hydration, viscous secretions, and iron pigments
    

  • FLAIR

    - Usually does not completely null
    

  • DWI

    - Characteristic hyperintensity
            - High fractional anisotropy due to diffusion along 2D geometric plane
                      - Attributed to microstructure of parallel-layered keratin filaments and flakes
            - In comparison to white matter, which also shows high fractional anisotropy, due to diffusion along single direction
    - ADC = brain parenchyma
    

  • T1WI C+

    - Usually none, though margin of cyst may show minimal enhancement (25%)
    - Enhancing tumor is sign of malignant degeneration
    

  • MRS

    - Resonances from lactate
    - No NAA, choline, or lipid
    

• Angiographic Findings

  • Conventional - Depending on location and size, may show avascular mass effect

• Nonvascular Interventions

  • Myelography

    - Cisternography contrast delineates irregular lobulated tumor borders, extends into interstices
    

• Imaging Recommendations

  • Best imaging tool

    - MR
    

  • Protocol advice

    - FLAIR will often distinguish, whereas conventional sequences may not
    - Diffusion restriction definitively distinguishes from arachnoid cyst
    

DIFFERENTIAL DIAGNOSIS

• Arachnoid Cyst
  • Usually isointense to CSF on all standard sequences - Completely nulls on FLAIR - Hypointense diffusion: Contains highly mobile CSF, ADC = stationary water
  • Rather than insinuate and engulf local structures, arachnoid cysts displace them
  • Smooth surface, unlike lobulations of epidermoids
• Inflammatory Cyst
  • i.e., neurocysticercosis
  • Often enhances
  • Density/signal intensity usually not precisely like CSF
  • Adjacent edema, gliosis common
• Cystic Neoplasm
  • Attenuation/signal intensity not that of CSF
  • Often enhances
• Dermoid Cyst
  • Usually at or near midline
  • Resembles fat, not CSF, and contains dermal appendages; often ruptured

PATHOLOGY

• General Features

  • Etiology

    - Congenital: Embryology
            - Arise from ectodermal inclusions during neural tube closure, 3rd to 5th week of embryogenesis
            - Congenital intradural CPA epidermoids derived from cells of 1st branchial groove
    - Acquired: Develop as result of trauma
            - Uncommon etiology for intracranial tumors
            - More common as spine etiology following LP
    

  • Genetics

    - Sporadic
    

  • Associated abnormalities

    - May have occipital/nasofrontal dermal sinus tract
    

• Gross Pathologic & Surgical Features

  • Outer surface often has shiny, glistening, mother-of-pearl appearance ("beautiful tumor")
  • Soft and pliable - Conforms to shape of adjacent local structures/spaces
  • Lobulated excrescences - May invaginate into brain
  • Insinuating growth pattern, extends through cisterns, surrounds and encases vessels/nerves
  • Cyst filled with soft, waxy, creamy, or flaky keratinaceous material

• Microscopic Features

  • Cyst wall = internal layer of simple stratified cuboidal squamous epithelium covered by fibrous capsule
  • Cyst contents = solid crystalline cholesterol, keratinaceous debris; no dermal appendages
  • Grows by progressive desquamation with conversion to keratin/cholesterol crystals, forming concentric lamellae

CLINICAL ISSUES

• Presentation

  • Most common signs/symptoms

    - Symptoms depend on location and effect on adjacent neurovascular structures
            - Most common symptom: Headache
            - Cranial nerves V, VII, VIII neuropathy common
            - 4th ventricular cerebellar signs common, yet increased intracranial pressure rare
            - Less commonly hypopituitarism, diabetes insipidus
            - Seizures if in sylvian fissure/temporal lobe
    - May remain clinically silent for many years
    

• Demographics

  • Age

    - Presents between 20-60 years with peak at 40 years
    - Presentation is uncommon in childhood
    

  • Sex

    - M = F
            - CT hyperdense variant lesions have female predominance (M:F = 1:2.5)
    

  • Epidemiology

    - Epidermoids make up 0.2-1.8% of all primary intracranial tumors
    - Much more common than dermoid cyst (4-9x higher incidence)
    - Most common congenital intracranial tumor
    - 3rd most common CPA/IAC mass, after vestibular schwannoma and meningioma
    

• Natural History & Prognosis

  • Grows slowly: Epithelial component growth rate commensurate to that of normal epithelium
  • Chemical meningitis possible from content leakage
  • Rare malignant degeneration into squamous cell carcinoma (SCCa) reported - Postulated prolonged or reparative process from foreign material leads to cellular atypia and neoplasia - Often predated by frequent recurrences - May occur years after surgical resection - Mean age at presentation: 52 years with male preponderance

• Treatment

  • Microsurgical resection - Complicated by investment of local structures - Recurrence common if cyst capsule incompletely removed - Subarachnoid dissemination of contents may occur during operative/postoperative course - May cause chemical meningitis - CSF seeding and implantation reported
  • Rare malignant degeneration of resection bed into SCCa reported

DIAGNOSTIC CHECKLIST

• Consider

  • Epidermoid if insinuates CSF spaces, surrounds arteries/CNs with minimal displacement

• Image Interpretation Pearls

  • Resembles CSF on imaging studies, except usually incomplete nulling on FLAIR
  • DWI hyperintensity is diagnostic

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References

Selected References

1. Pons Escoda A et al: Imaging of skull vault tumors in adults. Insights Imaging. 11(1):23, 2020
2. Bobeff EJ et al: Suprasellar Epidermoid Cyst: Case Report of Extended Endoscopic Transsphenoidal Resection and Systematic Review of the Literature. World Neurosurg. 128:514-26, 2019
3. Hitti FL et al: Endoscopic Resection of a Cerebellopontine Angle Epidermoid Cyst via a Retrosigmoid Approach. J Neurol Surg B Skull Base. 80(Suppl 3):S330, 2019
4. Ma J et al: Primary intradiploic epidermoid cyst: a case report with literature review. Clin Neuropathol. 38(1):28-32, 2019
5. Badat N et al: Malignant transformation of epidermoid cyst with diffuse leptomeningeal carcinomatosis on skull base and trigeminal perineural spread. J Neuroradiol. 45(5):337-40, 2018
6. Gollapudi PR et al: A frontal giant intradiploic giant pearl (epidermoid cyst) with intracranial and extracranial extension: a rare entity. J Pediatr Neurosci. 13(4):480-2, 2018
7. Twede JV et al: Intraosseous epidermoid cyst of the skull: case study and radiological imaging considerations. Dermatol Online J. 24(7), 2018
8. Vaz-Guimaraes F et al: Endoscopic endonasal surgery for epidermoid and dermoid cysts: a 10-year experience. J Neurosurg. 1-11, 2018
9. Aboud E et al: Giant intracranial epidermoids: is total removal feasible? J Neurosurg. 1-14, 2015
10. Law EK et al: Atypical intracranial epidermoid cysts: rare anomalies with unique radiological features. Case Rep Radiol. 2015:528632, 2015
11. Demir MK et al: Rare and challenging extra-axial brain lesions: CT and MRI findings with clinico-radiological differential diagnosis and pathological correlation. Diagn Interv Radiol. 20(5):448-52, 2014
12. Vellutini EA et al: Malignant transformation of intracranial epidermoid cyst. Br J Neurosurg. 28(4):507-9, 2014
13. Velamati R et al: Meningitis secondary to ruptured epidermoid cyst: case-based review. Pediatr Ann. 42(6):248-51, 2013
14. Ren X et al: Clinical, radiological, and pathological features of 24 atypical intracranial epidermoid cysts. J Neurosurg. 116(3):611-21, 2012
15. Li F et al: Hyperdense intracranial epidermoid cysts: a study of 15 cases. Acta Neurochir (Wien). 149(1):31-9; discussion 39, 2007

Images

Selected Images

Sagittal graphic shows a multilobulated epidermoid primarily within the prepontine cistern. Significant mass effect displaces the pons, cervicomedullary junction, and upper cervical spine.

Gross pathology shows an epidermoid cyst extending anterosuperiorly from the cerebellopontine angle (CPA) cistern, insinuating within the prepontine cistern and encasing the basilar artery . Note its typical pearly appearance. (Courtesy E. Hedley-Whyte, MD.)

Axial NECT shows a typical epidermoid cyst (EC) in an expanded right CPA cistern. Note that the EC is slightly more dense than the adjacent CSF and has a frothy, cauliflower-like surface.

MR shows CPA epidermoid cyst that resembles CSF on T1 and T2 but typically does not suppress on FLAIR and demonstrates moderate restricted diffusion .

Sagittal T1 MR in a 39-year-old woman with a history of attempted resection of a posterior fossa EC shows a large mass infiltrating the prepontine cistern and wrapping around the cervicomedullary junction . The mass is nearly isointense with CSF.

Axial PD MR in the same patient shows a lobulated mass in the right CPA cistern that is nearly isointense with CSF in the cistern and 4th ventricle .

Axial T2 MR in the same patient shows the mass is nearly as hyperintense as fluid in the CPA cistern and 4th ventricle .

Coronal T2 MR shows the lobulated, hyperintense mass encases and displaces the basilar artery . CSF in the right middle fossa is a cavity from prior attempted resection.

Axial FLAIR MR demonstrates that the lobulated, cauliflower-like mass in the right CPA and prepontine cistern does not suppress.

The mass restricts on DWI MR. This is a classic EC that infiltrates and insinuates CSF cisterns, encasing vessels (like the basilar artery) and cranial nerves (in this case, cranial nerves VII and VIII).

Additional Images

Gross pathology nicely shows the typical shiny, glistening, pearly appearance of an epidermoid residing within the prepontine cistern, which was also encasing the basilar artery (not shown).

Axial T2 MR shows a nearly CSF isointense epidermoid within the left anterior middle cranial fossa.

Axial DWI MR shows restricted diffusion within a left anterior middle cranial fossa epidermoid.

Axial T2 MR shows an extraaxial left occipital mass that scallops the skull and displaces the dura inwardly .

Axial T1 C+ FS MR in the same patient shows the mass does not enhance . DWI (not shown) clinched the diagnosis as an EC. This is an atypical location for epidermoid.

Axial bone CT in the same patient reveals significant yet benign-appearing remodeling and scalloping of the inner calvarial table .

Bone CT in a 16-year-old girl with nonspecific headaches shows a smoothly marginated, lytic, expansile mass centered on the diploic space of the calvarium.

Axial NECT in the same patient shows the calvarial cyst is hypodense relative to cortex. This is a classic EC of the skull and was an incidental finding in this asymptomatic patient.

Axial bone CT demonstrates the typical appearance of a large intradiploic epidermoid as an expansile lesion with sharply corticated margins .

Axial T2 MR in the same patient shows the lobulated, hyperintense mass scallops the skull . Intradiploic EC was removed at surgery.

Axial T1 (upper left), T2 (upper right) and FLAIR (lower left) MR show an extensive intradiploid EC. Coronal T1 C+ MR (lower right) shows mild enhancement around the cyst margin.

Axial T2 (upper left), FLAIR (upper right), T1 C+ (lower left), and DWI (lower right) MR show a recurrent EC that appears intraaxial, but the original surgery 24 years prior disclosed an EC of the quadrigeminal cistern.