Saturday 27 August 2011

Epidermoid cyst MRI

A 35 yo female with left side Trigeminal Neuralgia clinically.
Here is her MRI Brain Axial T1 T2 FLAIR and Diffusion. 
This MRI study of Brain shows:
A lobulated extra axial left Cp angle cystic space occupying lesion.
Signals hypo intense on T1, hyper intense T2w images, hypo intense on Flair but signal suppression of fluid is not complete, not as clear as csf.
Restricted diffusion on Dw images. 
Cyst is insinuating in cisternal spaces. Significant mass effect, adjacent left cerebellar hemisphere, brain stem and fourth ventricle are compressed, left side trigeminal nerve stretched.
No obvious parenchymal invasion.
Contrast enhanced T1w images not available.

Imaging diagnosis : left Cp angle Epidermoid cyst.

Closest differential is Arachnoid cyst which shows complete signal suppression of fluid on FLAIR, as clear as csf, no restricted diffusion on Dw images, an associated hypoplasia of adjacent brain parenchyma, mass effect if any is mild and not significant as in this case.

Left retro mastoid craniotomy perfomed. Epidermoid cyst confirmed by intraoperative and histopathological findings.


Belongs to a category of primary non neoplastic intracranial Cysts.

Intracranial epidermoids are congenital inclusion cysts, arise from ectodermal inclusions during neural tube closure. Acquired develops as a result of trauma and is very very rare.

EC contributes to 0.2-1.8% of all primary intracranial tumors.
4-9 times more common than dermoid.
EC is a most common congenital intracranial tumor and is third most common CPA/lAC mass, after vestibular schwannoma, meningioma.
Associated abnormalities may be occipital / naso frontal dermal sinus tract.

EC is a lobulated, irregular, "cauliflower-like" cystic mass with "fronds", insinuates cisterns and encases nerves/vessels. Restricted diffusion on MRI DWI is a diagnostic clue.

A. Intradural, in ~ 90% of cases, primarily in basal cisterns.
M/c is Cerebellopontine angle (40-50%), Fourth ventricle (~17%), Para sellar/middle cranial fossa (~10-15%), Rarely in cerebral hemispheres (~1.5%), Brain stem (rare), Intraventricular within tela choroidea of temporal horn, 3rd, or 4th ventricles.
B. Extradural, in ~ 10% , intradiploic to bony calvarium, spine.

Imaging findings
Often a round / lobulated mass, hypodense in more than 90% of cases, resembling a focal CSF density. In 10-25% an associated calcification noted.
"Dense" epidermoid – a rare variant secondary to hemorrhage, high protein, saponification of cyst debris to calcium soaps or iron-containing pigment.
Contrast enhancement is none. Very minimal enhancement may be present at its surface.
Intradiplioc epidermoid shows bony erosion with sharply corticated margins.

Signal on TlWI often slightly hyperintense to CSF.
Uncommonly hyperintense to brain ("white epidermoid") due to high triglycerides & unsaturated fatty acids
Uncommonly hypointense to CSF ("black epidermoid") due to presence of solid crystal cholesterol & keratin and lack of triglycerides & unsaturated fatty acids.
On T2WI, often isointense to slightly hyperintense to CSF.
Very rarely hypointense due to calcification, hydration, viscous secretions, iron pigments.
On FLAIR, hypo intense but slightly hyper intense than Csf due to incomplete suppression of fluid signals.
DWI, restricted diffusion is pathognomonic.
Post contrast Tl, usually none. Margin of cyst may show minimal enhancement.
MRS: lactate peaks.

EC grows by progressive desquamation with conversion to keratin/cholesterol crystals.
Gross features are outer surface often has shiny, glistening "mother of pearl" appearance ("beautiful tumor"), Cyst filled with soft, waxy, or flaky material. Lobulated excrescences. Soft and pliable, conforms to shape of adjacent local structures/spaces. Insinuating growth pattern (extends through cisterns, surrounds and encases vessels/nerves.
Microscopic Features are Cyst wall shows internal layer of simple stratified cuboidal squamous epithelium covered by fibrous capsule and contents is solid crystalline cholesterol, keratinaceous debris. No dermal appendages.

Clinical Presentation
Age of presentation is usually between 20-60 y with peak at 40; no gender preponderance.
Symptoms depend on location, growth pattern.
Headache is most common.
Cp angle lesion present with 5, 7,8 CN neuropathy.
Cerebellar signs.
Increased intracranial pressure rare due to 4th ventricular compression.
Less commonly hypopituitarism, diabetes insipidus.
Seizures if in Sylvian fissure/temporal lobe.
May remain clinically silent. Grows slowly.
Chemical meningitis possible from content leakage.
Rare malignant degeneration into squamous cell carcinoma (SCCa) reported.

Often surgical.
Complete resection often complicated by investment of local structures
Recurrence common if incompletely removed.
Subarachnoid dissemination of contents may occur during operative/postoperative course may cause chemical meningitis.
Rare malignant degeneration of resection bed into Sq Cell Ca reported, may occur years after surgical resection.

Reference: Diagnostic imaging Osborn.

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