447 lines
25 KiB
Markdown
447 lines
25 KiB
Markdown
---
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title: "Epidermoid Cyst"
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docid: "704c5ddf-e1f7-4a5d-a1b8-5b0e603170d9"
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authors:
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- key: "5cff4116-3654-4b3a-bb75-5ebe0b8c9850"
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value: "Anne G. Osborn, MD, FACR"
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breadcrumbs:
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-
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name: "Brain"
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slug: "brain"
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treeNodeId: "6d8829f1-14d7-45af-8675-255189aa526a"
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-
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name: "Diagnosis"
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slug: "diagnosis"
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treeNodeId: "51c00394-446e-4a38-94af-d3b1d14d34e8"
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-
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name: "Pathology-Based Diagnoses"
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slug: "pathology-based-diagnoses"
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treeNodeId: "d9d3a8ed-f21b-4831-8c77-591a3500ef77"
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-
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name: "Primary Nonneoplastic Cysts"
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slug: "primary-nonneoplastic-cysts"
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treeNodeId: "8037bffe-f61e-4433-b841-a263bcfbe056"
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-
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name: "Epidermoid Cyst"
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slug: "epidermoid-cyst"
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treeNodeId: null
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category: "Brain"
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documentVersionId: "4092685b-a22f-42ca-b14b-6a21122b651f"
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imageCount: 22
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lastUpdated: "06/12/20"
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pageDescription: "Epidermoid Cyst"
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pageKeywords: "Brain, Diagnosis, Pathology-Based Diagnoses, Primary Nonneoplastic Cysts, Epidermoid Cyst"
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pageTitle: "Epidermoid Cyst | STATdx"
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enhancedTitle: "Epidermoid Cyst"
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type: "DX"
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references: true
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breadcrumbs:
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- "Brain"
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- "Diagnosis"
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- "Pathology-Based Diagnoses"
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- "Primary Nonneoplastic Cysts"
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- "Epidermoid Cyst"
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---
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# KEY FACTS
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- ## Terminology
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- Intracranial epidermoids ("pearly" tumor)
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- Congenital ectodermal inclusion cysts, not true neoplasm
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- ## Imaging
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- CSF-like mass that insinuates cisterns and encases neurovascular structures
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- Morphology: Lobulated, irregular, cauliflower-like mass with "fronds"
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- FLAIR: Usually does not completely null
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- DWI: Diffusion restriction definitively distinguishes from arachnoid cyst
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- ## Top Differential Diagnoses
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- Arachnoid cyst
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- Inflammatory cyst (i.e., neurocysticercosis)
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- Cystic neoplasm
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- Dermoid cyst
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- ## Pathology
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- Arise from ectodermal inclusions during neural tube closure, 3rd to 5th week of embryogenesis
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- ## Clinical Issues
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- Symptoms depend on location and effect on adjacent neurovascular structures
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- Most common symptom: Headache
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- Cranial nerves V, VII, VIII neuropathy common
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- 0.2-1.8% of all primary intracranial tumors
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- Rare malignant degeneration into squamous cell carcinoma
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- Treatment: Microsurgical resection
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- Recurrence common if incompletely removed
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- ## Diagnostic Checklist
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- Insinuates CSF spaces, surrounds arteries, CNs with minimal displacement
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- Incomplete nulling on FLAIR; DWI hyperintense
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# TERMINOLOGY
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- ## Synonyms
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- Ectodermal inclusion cyst
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- "Pearly" tumor
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- ## Definitions
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- Intracranial epidermoids are congenital inclusion cysts (not "tumors")
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- Benign, slow-growing congenital lesions derived from ectodermal remnants sequestrated during embryogenesis
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- CSF-like mass that insinuates cisterns and encases neurovascular structures
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- ### Location
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- Intradural (90%), strong predilection for basal cisterns
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- Cerebellopontine angle (CPA) (40-50%)
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- 4th ventricle (17%)
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- Parasellar/middle cranial fossa/sylvian fissure (10-15%)
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- Parenchymal (i.e., cerebral hemispheres) rare (1.5%)
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- Brainstem exceedingly rare
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- Extradural (10%)
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- Skull (intradiploic within frontal, parietal, occipital, sphenoid skull) as well as spine
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- ### Size
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- Variable; extradural intradiploic variants can become huge with minimal/no neurologic deficits
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- Grow slowly by desquamation of normal cells into cystic cavity
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- ### Morphology
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- Lobulated, irregular, cauliflower-like excrescences
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- Insinuates without mass effect unless large
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- ## Radiographic Findings
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- ### Radiography
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- Diploic space epidermoids
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- May alter scalp, outer/inner skull tables, and epidural space appearance
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- Typically round or lobulated
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- Well delineated with sclerotic rim
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- ## CT Findings
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- ### NECT
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- Round/lobulated mass
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- > 95% hypodense, resembling CSF
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- 10-25% contain calcifications
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- Rare variant = "dense" epidermoid
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- 3% of intracranial epidermoids
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- Secondary to hemorrhage, high protein, saponification of cyst debris to calcium soaps or iron-containing pigment
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- ### CECT
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- Usually none, though margin of cyst may show minimal enhancement
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- ### Bone CT
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- May have bony erosion; sharply corticated margins when intradiploic
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- ## MR Findings
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- ### T1WI
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- Often (~ 75%) slightly hyperintense to CSF
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- Lobulated periphery may be slightly more hyperintense than center
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- Uncommonly hyperintense to brain ("white epidermoid") due to high triglycerides and unsaturated fatty acids
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- Uncommonly hypointense to CSF ("black epidermoid")
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- Presence of solid crystal cholesterol and keratin
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- Lack of triglycerides and unsaturated fatty acids
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- ### T2WI
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- Often isointense (65%) to slightly hyperintense (35%) to CSF
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- Very rarely hypointense due to calcification, ↓ hydration, viscous secretions, and iron pigments
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- ### FLAIR
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- Usually does not completely null
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- ### DWI
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- Characteristic hyperintensity
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- High fractional anisotropy due to diffusion along 2D geometric plane
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- Attributed to microstructure of parallel-layered keratin filaments and flakes
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- In comparison to white matter, which also shows high fractional anisotropy, due to diffusion along single direction
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- ADC = brain parenchyma
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- ### T1WI C+
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- Usually none, though margin of cyst may show minimal enhancement (25%)
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- Enhancing tumor is sign of malignant degeneration
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- ### MRS
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- Resonances from lactate
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- No NAA, choline, or lipid
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- ## Angiographic Findings
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- Conventional
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- Depending on location and size, may show avascular mass effect
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- ## Nonvascular Interventions
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- ### Myelography
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- Cisternography contrast delineates irregular lobulated tumor borders, extends into interstices
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- ## Imaging Recommendations
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- ### Best imaging tool
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- MR
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- ### Protocol advice
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- FLAIR will often distinguish, whereas conventional sequences may not
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- Diffusion restriction definitively distinguishes from arachnoid cyst
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# DIFFERENTIAL DIAGNOSIS
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- [Arachnoid Cyst](/document/arachnoid-cyst/d25aaeb3-5b3c-4483-99dc-2757468eedb9)
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- Usually isointense to CSF on all standard sequences
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- Completely nulls on FLAIR
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- Hypointense diffusion: Contains highly mobile CSF, ADC = stationary water
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- Rather than insinuate and engulf local structures, arachnoid cysts displace them
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- Smooth surface, unlike lobulations of epidermoids
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- [Inflammatory Cyst](/document/neurocysticercosis/6a45835f-6d7c-443e-874a-f33131d3def1)
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- i.e., neurocysticercosis
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- Often enhances
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- Density/signal intensity usually not precisely like CSF
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- Adjacent edema, gliosis common
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- [Cystic Neoplasm](/document/pilocytic-astrocytoma/7eca92f5-6caa-4300-9afe-1b733b4473b2)
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- Attenuation/signal intensity not that of CSF
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- Often enhances
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- [Dermoid Cyst](/document/dermoid-cyst/9b7aeb04-2cb3-405d-8c51-dd13297dd67c)
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- Usually at or near midline
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- Resembles fat, not CSF, and contains dermal appendages; often ruptured
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Congenital: Embryology
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- Arise from ectodermal inclusions during neural tube closure, 3rd to 5th week of embryogenesis
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- Congenital intradural CPA epidermoids derived from cells of 1st branchial groove
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- Acquired: Develop as result of trauma
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- Uncommon etiology for intracranial tumors
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- More common as spine etiology following LP
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- ### Genetics
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- Sporadic
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- ### Associated abnormalities
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- May have occipital/nasofrontal dermal sinus tract
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- ## Gross Pathologic & Surgical Features
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- Outer surface often has shiny, glistening, mother-of-pearl appearance ("beautiful tumor")
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- Soft and pliable
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- Conforms to shape of adjacent local structures/spaces
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- Lobulated excrescences
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- May invaginate into brain
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- Insinuating growth pattern, extends through cisterns, surrounds and encases vessels/nerves
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- Cyst filled with soft, waxy, creamy, or flaky keratinaceous material
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- ## Microscopic Features
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- Cyst wall = internal layer of simple stratified cuboidal squamous epithelium covered by fibrous capsule
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- Cyst contents = solid crystalline cholesterol, keratinaceous debris; no dermal appendages
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- Grows by progressive desquamation with conversion to keratin/cholesterol crystals, forming concentric lamellae
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- Symptoms depend on location and effect on adjacent neurovascular structures
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- Most common symptom: Headache
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- Cranial nerves V, VII, VIII neuropathy common
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- 4th ventricular cerebellar signs common, yet increased intracranial pressure rare
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- Less commonly hypopituitarism, diabetes insipidus
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- Seizures if in sylvian fissure/temporal lobe
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- May remain clinically silent for many years
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- ## Demographics
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- ### Age
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- Presents between 20-60 years with peak at 40 years
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- Presentation is uncommon in childhood
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- ### Sex
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- M = F
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- CT hyperdense variant lesions have female predominance (M:F = 1:2.5)
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- ### Epidemiology
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- Epidermoids make up 0.2-1.8% of all primary intracranial tumors
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- Much more common than dermoid cyst (4-9x higher incidence)
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- Most common congenital intracranial tumor
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- 3rd most common CPA/IAC mass, after vestibular schwannoma and meningioma
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- ## Natural History & Prognosis
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- Grows slowly: Epithelial component growth rate commensurate to that of normal epithelium
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- Chemical meningitis possible from content leakage
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- Rare malignant degeneration into squamous cell carcinoma (SCCa) reported
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- Postulated prolonged or reparative process from foreign material leads to cellular atypia and neoplasia
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- Often predated by frequent recurrences
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- May occur years after surgical resection
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- Mean age at presentation: 52 years with male preponderance
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- ## Treatment
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- Microsurgical resection
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- Complicated by investment of local structures
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- Recurrence common if cyst capsule incompletely removed
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- Subarachnoid dissemination of contents may occur during operative/postoperative course
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- May cause chemical meningitis
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- CSF seeding and implantation reported
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- Rare malignant degeneration of resection bed into SCCa reported
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- Epidermoid if insinuates CSF spaces, surrounds arteries/CNs with minimal displacement
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- ## Image Interpretation Pearls
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- Resembles CSF on imaging studies, except usually incomplete nulling on FLAIR
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- DWI hyperintensity is diagnostic
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da5731a9-6c09-4bf5-99d9-fdefe09d5800
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## References
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# Selected References
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1. [Pons Escoda A et al: Imaging of skull vault tumors in adults. Insights Imaging. 11(1):23, 2020](http://www.ncbi.nlm.nih.gov/pubmed/?term=32056014%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=31121364%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=31143618%5Bpmid%5D)
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1. [Ma J et al: Primary intradiploic epidermoid cyst: a case report with literature review. Clin Neuropathol. 38(1):28-32, 2019](http://www.ncbi.nlm.nih.gov/pubmed/?term=30526818%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=30036548%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=30937095%5Bpmid%5D)
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1. [Twede JV et al: Intraosseous epidermoid cyst of the skull: case study and radiological imaging considerations. Dermatol Online J. 24(7), 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=30261578%5Bpmid%5D)
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1. [Vaz-Guimaraes F et al: Endoscopic endonasal surgery for epidermoid and dermoid cysts: a 10-year experience. J Neurosurg. 1-11, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29547084%5Bpmid%5D)
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1. [Aboud E et al: Giant intracranial epidermoids: is total removal feasible? J Neurosurg. 1-14, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25594324%5Bpmid%5D)
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1. [Law EK et al: Atypical intracranial epidermoid cysts: rare anomalies with unique radiological features. Case Rep Radiol. 2015:528632, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25667778%5Bpmid%5D)
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1. [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](http://www.ncbi.nlm.nih.gov/pubmed/?term=25010368%5Bpmid%5D)
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1. [Vellutini EA et al: Malignant transformation of intracranial epidermoid cyst. Br J Neurosurg. 28(4):507-9, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24345076%5Bpmid%5D)
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1. [Velamati R et al: Meningitis secondary to ruptured epidermoid cyst: case-based review. Pediatr Ann. 42(6):248-51, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23718247%5Bpmid%5D)
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1. [Ren X et al: Clinical, radiological, and pathological features of 24 atypical intracranial epidermoid cysts. J Neurosurg. 116(3):611-21, 2012](http://www.ncbi.nlm.nih.gov/pubmed/?term=22175719%5Bpmid%5D)
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1. [Li F et al: Hyperdense intracranial epidermoid cysts: a study of 15 cases. Acta Neurochir (Wien). 149(1):31-9; discussion 39, 2007](http://www.ncbi.nlm.nih.gov/pubmed/?term=17151831%5Bpmid%5D)
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## Images
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### Selected Images
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*Sagittal graphic shows a multilobulated epidermoid primarily within the prepontine cistern. Significant mass effect displaces the pons, cervicomedullary junction, and upper cervical spine.*
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*Gross pathology shows an epidermoid cyst extending anterosuperiorly from the cerebellopontine angle (CPA) cistern, insinuating within the prepontine cistern and encasing the basilar artery <img src='img/arrows/BO.png'/>. Note its typical pearly appearance. (Courtesy E. Hedley-Whyte, MD.)*
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*Axial NECT shows a typical epidermoid cyst (EC) in an expanded right CPA cistern. Note that the EC <img src='img/arrows/WS.png'/> is slightly more dense than the adjacent CSF <img src='img/arrows/WC.png'/> and has a frothy, cauliflower-like surface.*
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*MR shows CPA epidermoid cyst that resembles CSF on T1 and T2 <img src='img/arrows/WS.png'/> but typically does not suppress on FLAIR <img src='img/arrows/BO.png'/> and demonstrates moderate restricted diffusion <img src='img/arrows/WO.png'/>.*
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*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 <img src='img/arrows/BO.png'/> and wrapping around the cervicomedullary junction <img src='img/arrows/WC.png'/>. The mass is nearly isointense with CSF.*
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*Axial PD MR in the same patient shows a lobulated mass <img src='img/arrows/BS.png'/> in the right CPA cistern that is nearly isointense with CSF in the cistern and 4th ventricle <img src='img/arrows/BO.png'/>.*
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*Axial T2 MR in the same patient shows the mass <img src='img/arrows/WS.png'/> is nearly as hyperintense as fluid in the CPA cistern and 4th ventricle <img src='img/arrows/WO.png'/>.*
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*Coronal T2 MR shows the lobulated, hyperintense mass <img src='img/arrows/WS.png'/> encases and displaces the basilar artery <img src='img/arrows/WO.png'/>. CSF in the right middle fossa <img src='img/arrows/WC.png'/> is a cavity from prior attempted resection.*
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*Axial FLAIR MR demonstrates that the lobulated, cauliflower-like mass <img src='img/arrows/WS.png'/> in the right CPA and prepontine cistern does not suppress.*
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*The mass <img src='img/arrows/WS.png'/> 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).*
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### Additional Images
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*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).*
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*Axial T2 MR shows a nearly CSF isointense epidermoid within the left anterior middle cranial fossa.*
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*Axial DWI MR shows restricted diffusion within a left anterior middle cranial fossa epidermoid.*
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*Axial T2 MR shows an extraaxial left occipital mass that scallops the skull <img src='img/arrows/WO.png'/> and displaces the dura inwardly <img src='img/arrows/WS.png'/>.*
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*Axial T1 C+ FS MR in the same patient shows the mass does not enhance <img src='img/arrows/WS.png'/>. DWI (not shown) clinched the diagnosis as an EC. This is an atypical location for epidermoid.*
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*Axial bone CT in the same patient reveals significant yet benign-appearing remodeling and scalloping of the inner calvarial table <img src='img/arrows/WO.png'/>.*
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*Bone CT in a 16-year-old girl with nonspecific headaches shows a smoothly marginated, lytic, expansile mass <img src='img/arrows/WC.png'/> centered on the diploic space of the calvarium.*
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*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.*
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*Axial bone CT demonstrates the typical appearance of a large intradiploic epidermoid as an expansile lesion with sharply corticated margins <img src='img/arrows/BS.png'/>.*
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*Axial T2 MR in the same patient shows the lobulated, hyperintense mass scallops the skull <img src='img/arrows/WS.png'/>. Intradiploic EC was removed at surgery.*
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*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 <img src='img/arrows/WS.png'/> around the cyst margin.*
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*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.*
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