Epidermoid diagnostic via imaging
Discussion: There are congenital and acquired epidermoid cysts. Congenital type is a non-neoplastic inclusion of ectoderm during neural tube closure or formation of secondary cerebral vesicles. Acquired type is implanted epidermis, usually by nonstylet needle punctures (as in lumbar puncture). Grossly, it is a well-defined lobulated cystic lesion, which insinuates along CSF cisterns.
The interior is filled with keratohyalin from continued desquamation by the epithelium. It encases vessels and nerves and can invaginate deeply into the brain. It does not contain hair follicles or sebaceous glands (dermoid cyst). Age=20-60. 0.2 to 1% of all primary intracranial neoplasm/neoplastic-like growths. 90% are intradural. Off-midline sites are common. 40-50% are in the CPA cisterns. Intraaxial type tends to be in the fourth ventricle. Local recurrence is common. No metastases (not really a neoplasm). NCE CT appearance is a lucent lobulated mass, 10-25% calcify. MRI appearance is a lobulated mass mostly confined to and insinuating in basilar cisterns. Rim signal can be slightly higher; contents have signal similar to CSF. If iso- or hypointense to brain on T1W, it is labelled a “white epidermoid” because of high lipid content. Diffusion weighting can potentially differentiate an arachnoid cyst (ADC like water) from epidermoid (ADC like brain parenchyma).
References:
- Osborn, Anne G., Diagnostic Radiology, Mosby, St. Louis, MO, pp.631-35, 1994.
- Mafee, M.F. et al, Epidermoid cysts…, Neuroimaging Clinics of North America, 4(3): 561-78, 1994 Aug.
Findings:
Image 1:(T1W Sagittal) Invagination of the brainstem and cerebellum by a lobulated structure filled with material close to CSF intensity.
Image 2: (T2W Axial) Structure follows CSF intensity. Insinuates around normal structures (vessels, nerves). Compresses cerebral aqueduct. Located in left CPA and extends midline.
Image 3: (T1W Axial pre-con) Mass is centered in left CPA and may enter IAC.
Image 4: (T1W Axial post-con) essentially non-enhancing.
Image 5: (T1W Coronal post-con) Left greater than right ventriculomegaly–probably chronic obstruction at cerebral aqueduct by the mass with compensation. Again, no enhancement. Another view of the mass insinuating around normal structures and invaginating the brainstem.
Diagnosis: Extraaxial Epidermoid
Diagnostic Method: Imaging
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Source: Teaching File Case P0432, University of Colorado Health Sciences Center
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