Epidermoid tumor of cerebello-pontine angle (ET), also known as cholesteatoma or pearly tumor, is a benign slow-growing congenital lesion. It is 0.7 - 1.8% of all intracranial tumors. Its most frequent localization is in the cerebellopontine angle (CPA) and it comprises 4.6% to 6.3% of all masses in this region. ET originates from ectopic inclusions of epithelial cells during neural tube closure (3rd - 5th weeks of embryogenesis). Lumbar punctures may, albeit rarely, cause epidermoid cysts to develop. Macroscopically, the outer surface of the cyst is shiny, and the wall avascular and adherent to vessels, nerves, meninges, and the choroid plexus. Focal calcification of the capsule may be present. Histologically, it has a stratified squamous epithelium, and contains keratin, cellular debris, and cholesterol.
Best imaging tools: brain MR with FLAIR, DWI & enhanced T1 sequences. MR findings: T1WI - isointense or slightly hyperintense to cerebrospinal fluid (CSF), white epidermoid has a high T1 signal; T2WI - isointense to hyperintense compared to CSF, white epidermoid has a low T2 signal; FLAIR - lack of any attenuation or “incomplete attenuation” on FLAIR is suggestive of ET of CPA; DWI - high signal on diffusion scans makes diagnosis; T1 C+ - no enhancement is a rule, only a peripheral enhancement occurs in 25% of cases.
Clinical presentation: neuropathy, cerebellar signs, and progressive hemiparesis. The trigeminal nerve and the acoustic-facial bundle may be involved causing hemifacial spasm and/or trigeminal neuralgia. A history of Mollaret meningitis may be present (recurrent aseptic meningitis). Complete surgical removal is the goal treatment. Total removal is possible in < 50% of the cases. Near total removal is often the better surgical choice because there are often dense adhesions between the tumor capsule and the neuro-vascular structures of the CPA. In cases or recurrence, it takes many years to grow.
Best imaging tools: brain MR with FLAIR, DWI & enhanced T1 sequences. MR findings: T1WI - isointense or slightly hyperintense to cerebrospinal fluid (CSF), white epidermoid has a high T1 signal; T2WI - isointense to hyperintense compared to CSF, white epidermoid has a low T2 signal; FLAIR - lack of any attenuation or “incomplete attenuation” on FLAIR is suggestive of ET of CPA; DWI - high signal on diffusion scans makes diagnosis; T1 C+ - no enhancement is a rule, only a peripheral enhancement occurs in 25% of cases.
Clinical presentation: neuropathy, cerebellar signs, and progressive hemiparesis. The trigeminal nerve and the acoustic-facial bundle may be involved causing hemifacial spasm and/or trigeminal neuralgia. A history of Mollaret meningitis may be present (recurrent aseptic meningitis). Complete surgical removal is the goal treatment. Total removal is possible in < 50% of the cases. Near total removal is often the better surgical choice because there are often dense adhesions between the tumor capsule and the neuro-vascular structures of the CPA. In cases or recurrence, it takes many years to grow.
References
- Handbook of Neurosurgery - fifth edition - Mark S. Greenberg - ed. Thieme.
- Ross JS, Brant-Zawadzki M, Moore KR, et al.. Diagnostic Imaging Spine. First edition - Amirsys - Elsevier Saunders - 2004.
- Bikmaz K. Management of cerebellopontine angle epidermoid tumors. Contemporary Neurosurgery 26;(14): July 15, 2004.
