Compressive optic neuropathy and ependymoma of the third ventricle.

Progressive monocular visual loss was the presenting manifestation of a cystic ependymoma arising from the third ventricle. Extracerebral extension of the tumor into the prechiasmatic cistern compressed the right optic nerve. Subfrontal extension caused erosion of the planum sphenoidale. Subtotal excision of the tumor was followed by cranial irradiation, and no further visual loss occurred. Extracerebral growth of primary intracerebral gliomas may cause optic neuropathy that is indistinguishable from other compressive neuropathies.