Symptomatic neuroepithelial cysts in the posterior cranial fossa. Immunohistochemical and electron-microscopic studies.

A 2-year-old boy had increased intracranial pressure and convulsions because of two extraventricular cysts in the posterior cranial fossa. Releasing the watery cyst contents resulted in disappearance of such clinical manifestations. Immunohistochemically, the epithelial cytoplasm of the cyst was strongly positive for glial fibrillary acidic protein. Electron-microscopically, the cells that lined the cysts had microvilli which were coated with finely granular material to represent "fuzzy" coat, intercellular junctions linking the plasma membranes of adjacent cells, and numerous cytoplasmic glial filaments. The strong positivity for glial fibrillary acidic protein, then, is well correlated with an abundance of the latter. Cilia were also identified. Thus, the cysts were unequivocally neuroepithelial (ependymal) cysts. Only nine cases of neuroepithelial cysts in the posterior cranial fossa, including the current one, have been reported. Three patients were children; six were adults. The age of the patients ranged from 7 months to 60 years. The average age was 21.7 years The sex was known in eight patients with a male to female ratio of 3:5. The pathogenesis of these neuroepithelial cysts was proposed as related to developmental anomalies.