Pupil-sparing oculomotor palsy caused by fusiform arteriosclerotic aneurysm of the basilar artery--a case report.

Paresis of the oculomotor nerve is a very rare complication of an unruptured arteriosclerotic fusiform aneurysm of the basilar artery. A handful of cases are described in the world literature. A fifty-four-year-old man with a history of hypertension and diabetes mellitus presented with painless partial oculomotor palsy of sudden onset. A cerebral angiogram demonstrated a tortuous fusiform deformity of the basilar artery and the origin of the posterior cerebral arteries, indicative of an arteriosclerotic aneurysmal dilation. A sudden onset of a pupil-sparing ophthalmoplegia is the typical history of a microvascular infarct of the third nerve, whereas pupillary sparing in aneurysmal oculomotor paresis is a very rare event. Special emphasis has been placed on the pupillary size as a guide for the indication of arteriography. The many exceptions to this rule suggest that cerebral arteriography may be indicated more often than generally believed.