Hydrocephalus after posterior fossa operations.

Sixteen patients with hydrocephalus which developed after operations on the posterior fossa were studied by radioisotope ventriculography. The results indicate that postoperative hydrocephalus is of communicating type, and that block of the basal cisterns is always present. Mechanisms involved in its pathogenesis are discussed, and it is felt that pre-existent adhesions in basal cisterns, surgical bleeding and cerebrospinal fluid (CSF) extra-arachnoidal collections are possible causes of the hydrocephalus.