[A case of arachnoid cyst in the middle cranial fossa presenting with trigeminal neuralgia].

A 50-year-old man had been suffering from left trigeminal neuralgia for 30 years. CT scan revealed an arachnoid cyst occupying the anterior two-thirds of the left middle cranial fossa. Cerebral angiography showed elevation of the left middle cerebral artery and medial shift of the left posterior cerebral artery. Metrizamide CT showed that the cyst was not communicating with the subarachnoid space. Air CT revealed the root of the left trigeminal nerve in contact with the arachnoid cyst. The patient became completely free from the trigeminal neuralgia 6 months after cystoperitoneal shunt. This case seems to be a very rare case of trigeminal neuralgia caused by an arachnoid cyst.