Intracavernous sinus arachnoid cyst with optic neuropathy.

An 18-year-old man experienced progressive decreased visual acuity associated with a redness of the right eye for 1 month. An arachnoid cyst was identified within the right cavernous sinus and fenestration to the basal cistern was performed with the aid of a neuroendoscope. Visual acuity improved dramatically after the operation. Intracavernous sinus arachnoid cyst is a rare congenital intracranial lesion and surgical decompression may benefit symptomatic patients.