Unusual neuro-ophthalmic presentation of anterior communicating artery aneurysm with third nerve paresis.

Paresis of the oculomotor nerve associated with subarachnoid haemorrhage is considered a hallmark of aneurysms located at the junction of the internal carotid artery and posterior communicating artery. Third nerve palsy can also be caused by those aneurysms located in the intracavernous part of the internal carotid artery, basilar artery, posterior cerebral artery and superior cerebellar artery. However, oculomotor nerve paresis caused by an anterior communicating artery aneurysm is a very uncommon occurrence. We report a case of an elderly female with sudden severe headache who developed an acute third nerve paresis. Angiography revealed an anterior communicating artery aneurysm. Management and the pertinent literature are reviewed along with the mechanism of third nerve compression.