Ventral brain-stem compression from a subarachnoid ependymal cyst.

A case of ventral brain-stem compression by a congenital subarachnoid ependymal cyst in an infant is presented. Marsupialization of the cyst provided effective decompression and clinical improvement. Immunohistochemical staining demonstrated the glial nature of the epithelium. The fact that these cysts may be congenital, as demonstrated here, supports the hypothesis that they arise from glial elements that have been displaced during development.