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Neuroradiology Case of the Week

Case 361

November 2008

Hisao Nakamura, MD

Clinical Presentation: Patient is a 33-year old man with worsening headaches over a two month duration.

Imaging Findings: Epidermoid cyst with remote hemorrhage and gliosis.

Diagnosis: Epidermoid cyst

Discussion: Intracranial epidermoid tumors are congenital cystic lesions that arise from epithelial inclusions at the time of neural tube closure or during formation of the secondary cerebral vesicles. They are most common in the cerebellopontine angle and suprasellar and parasellar regions. The cysts are consistently circumscribed, with a smooth or irregular nodular capsular surface, and are usually filled with soft, white material, which is the result of progressive desquamation and breakdown of keratin from the epithelial lining. Epidermoid tumors are depicted by MR imaging as slightly hyperintense relative to CSF on T1-, T2-, and proton density-weighted sequences. DWI shows clear depiction. MR signals depend on the relative composition of cholesterol and keratin of the cystic contents. This case is high signal on T1 WI because the cysts include high protein concentration, mild calcification, and paramagnetic effects. This case is intermediate signal intensity on T2 WI. The signal intensity decreases with increasing protein concentration. Depending primarily on the percentage of protein and free water it contains, the proteinaceous fluid of epidermoids can have variable signal intensity on T2-weighted images. We assumed that a relatively high protein concentration was the major factor of signal intensity on MRI.

References:

1. Ochi M, Hayashi K, Hayashi T, et al. Unusual CT and MR appearance of an epidermoid tumor of the cerebellopontine angle. AJNR Am J Neuroradiol. 1998 Jun-Jul;19(6):1113-5. [PubMed]