[An epithelial cyst at the frontal convexity].

We report a rare case of an epithelial cyst at the right frontal convexity. A 60-year-old woman came to our hospital suffering from dysarthria and gait disturbance. Computed tomography (CT) of the brain on admission showed a round low-density area, 6 cm in diameter, at the right frontal convexity. Midline shift and displacement of the lateral ventricle are seen. There is no contrast enhancement effect. Excision of the cyst wall and fenestration into the subarachnoid space was carried out and the patient was discharged with no neurological deficits. After 5 years, regrowth of the cyst was seen. Cyst-peritoneal shunt was performed and she was discharged uneventfully. Light microscopy showed the cyst wall consisted of a monolayer of flat epithelium and loose connective tissue. An electronmicrograph of the cyst wall showed a non-ciliated epithelial layer with microvilli and basement membrane. The epithelial cells connecting with each other through desmosome have numerous endoplasmic reticulum and mitochondria. Interdigitation of the cytoplasmic membrane was not seen. The term "epithelial cyst" seems ambiguous. We discuss the pathogenesis and the nomenclature for intracranial benign cystic lesions based on the previous literature.