Chemical Analysis of an Epidermoid Cyst
Chemical Analysis of an Epidermoid Cyst with Unusual CT and MR Characteristics
Authors: F. A. Timmer, M. Sluzewski, M. Treskes, W. J. J. van Rooij, J. L. J. M. Teepen, and D. Wijnalda
Summary: Chemical analysis of the contents of a so-called bright epidermoid of the posterior fossa with unusual CT and MR imaging characteristics suggested that a combination of high protein content and high viscosity were responsible for the atypical imaging findings.
Epidermoid tumors are rare congenital lesions of the brain that account for 0.2% to 1% of all intracranial neoplasms (1). We report a case of an epidermoid tumor with an unusually dense appearance on CT scans, high signal intensity on T1-weighted MR images, and low signal intensity on T2-weighted MR images. The results of pathologic examination and chemical analysis of the contents of the cyst are discussed.
Case Report
A 47-year-old woman had a 10-year history of bilateral facial nerve paresis, deafness, and tongue atrophy. More recently, the symptoms had worsened and she reported difficulty swallow- ing. CT scans showed a dense mass in the posterior fossa of the left cerebellar hemisphere (Fig 1A). At MR imaging, the lesion showed high signal intensity on T1-weighted sequences and low signal intensity on T2-weighted sequences (Fig 1B and C). A small nodule was present at the periphery of the lesion. No enhancement was seen after administration of gadopentetate dimeglumine. On both the CT and MR studies, an arachnoid cyst was seen on the right side of the posterior fossa. The epidermoid showed mass effect on the brain stem. There was no hydrocephalus.
At surgery, a dark brown cyst with highly viscous, toffeelike contents was found and removed. The arachnoidal cyst was also evacuated. At pathologic examination, the cystic wall was composed of fibrous tissue lined with stratified squamous epithelium, consistent with the diagnosis of epidermoid. The cystic wall was partly disintegrated by chronic inflammation, with foreign-body reaction and reactive fibrous proliferation. This proliferation corresponded to the peripheral nodule seen at MR imaging.
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