Arachnoidal cyst invading the orbit.

Ipsilateral glaucoma developed in a 51-year-old man with a left-sided temporal lobe arachnoidal cyst. Ultrasonic examination disclosed a cystic orbital lesion adjacent to the optic nerve. Following intracranial decompensation of the arachnoidal cyst, the intraocular pressure dropped markedly. Ultrasonography showed a collapse of the presumed optic nerve sheath cyst. While the exact mechanism producing glaucoma in this patient remains unclear, there was an apparent relationship between the elevated intraocular pressure and the arachnoidal cyst.