Splitting and Penetration of the Optic Nerve by an Unruptured Aneurysm arising from the Anterior Communicating Artery

Abstract

A 54-year-old man presented with an unusual case of splitting and penetration of the optic nerve by a cerebral aneurysm. He suffered sudden onset of headache. Computed tomography showed subarachnoid hemorrhage. Cerebral angiography revealed aneurysms on the right middle cerebral artery, right internal carotid artery-posterior communicating artery bifurcation, and anterior communicating artery. Right frontotemporal craniotomy revealed the right middle cerebral artery aneurysm was covered with hematoma and presumably ruptured, and the unruptured right internal carotid artery-posterior communicating artery bifurcation aneurysm. Both aneurysms were clipped. The unruptured anterior communicating artery aneurysm was then revealed to have penetrated the left optic nerve. This aneurysm was clipped without detachment from the optic nerve. Postoperatively, visual field testing demonstrated enlarged Mariotte's blind spots in both eyes and lower medial quadrant hemianopsia in the left eye. No visual field deficit had been detected 3 years previously. The left quadrant hemianopsia had probably been present preoperatively, since no optic nerve damage occurred during the operation. The anterior communicating artery aneurysm had probably grown slowly and eventually penetrated the optic nerve, resulting in the visual field deficit.