[Hydrocephalus due to membranous obstruction of the fourth ventricle aperture].

Three cases of hydrocephalus due to membranous obstruction of the fourth ventricle aperture are reported. Patient's age was 4, 34 and 68 years old and they complained of slowly progressive cerebellar ataxia, gait disturbance and other hydrocephalic symptoms. CT scan revealed symmetrical dilatation of lateral ventricles, and, especially, the fourth ventricle aperture was confirmed by ventriculography or metrizamide CT cisternography. Suboccipital craniectomy was performed in all cases and cerebellum was of normal shape and semilucent membrane was found obliterating the foramen of Magendie. Histological finding of the membrane was chiefly composed of fibroblast, but inflammatory evidence suggesting any particular etiological process. The cause of membranous obstruction was undetermined and obsolete infectious or inflammatory change was suspected.