Arachnoid cysts of the posterior fossa.

A series of 6 patients with arachnoid cysts of the posterior fossa who were treated surgically is presented. The diagnosis of the nature of the lesion and of the exact location within the posterior fossa could not be established on a clinical basis. CT scanning is the best method for diagnosing the lesion and for observing the postoperative evolution. Treatment consisted of removing the cyst walls, shunting the cyst to the peritoneum, or both. The differential diagnosis of arachnoid cysts of the posterior fossa from other cerebrospinal fluid collections, such as the megacisterna magna or the Dandy-Walker malformation, are discussed.