Minimal oculomotor nerve paresis secondary to unruptured intracranial aneurysm

In 12 patients with minimal oculomotor nerve deficits due to unruptured intracranial aneurysm, the nerve-related findings were incomplete and at least one element (ptosis, mydriasis, or extraocular muscle weakness) was spared in every patient. Although symptomatic, the affected cranial nerve III functions were only partially lost. Six patients had ptosis and mydriasis, three had ptosis and diplopia, two had mydriasis and diplopia, and one had mydriasis alone. Eleven patients had accompanying headaches that were remarkably variable and difficult to categorize. Cerebral angiography showed the aneurysms, but computed tomography missed one third of them. The symptomatic aneurysm arose from the internal carotid artery in six patients, and from the distal basilar artery in six. Fragments of a cranial nerve III palsy associated with recent onset and ipsilateral headache suggest an enlarging internal carotid or distal basilar artery aneurysm.