Prepontine epithelium-lined cyst. Case report.

A 30-year-old woman presented with recurrent episodes of severe headache associated with visual disturbances. Neurological examination showed minimal neurological defects. Angiography, computerized tomography, and radioisotope cisternography revealed a large cyst in the prepontine region, which did not communicate with either the subarachnoid space or the ventricular system. Histologically, the cyst was lined by columnar and/or cuboidal cells, which contained materials positive on periodic acid-Schiff staining. Ultrastructurally, there were two types of cells, ciliated and noncillated. Characteristic findings were continuous basement membrane, microvilli covered with electron-dense material, several intercellular junctional devices, and an open intercellular space which was occasionally filled with a migrating cell. These findings would support the view that the epithelial cyst with such features was derived from endodermal tissues rather than from neuroepithelium. Electron microscopic examination is indispensable in making a correct diagnosis of intracranial cysts.