Arachnoid cysts of the posterior fossa.

The clinical symptoms and signs of four patients with arachnoid cysts in the posterior fossa are discussed. In three patients, the cyst was in the internal auditory canal; one patient had an acoustic neuroma and two large cysts in the cerebellum. Whereas the conventional diagnostic tests for acoustic neuroma cannot differentiate between neuromas and arachnoid cysts, the newer thin section body scanners can show a lesion with no enhancement in the case of the cyst. Surgical approaches for removal of this lesion must take into consideration the preservation of hearing in the involved ear.