Pupillary sparing in oculomotor palsy from internal carotid aneurysm

The authors report a patient with a carotid-posterior communicating artery aneurysm; although the oculomotor palsy accompanying such an aneurysm is almost universally recognized as being complete, with pupillary involvement, this patient had pupillary sparing the absence of subarachnoid bleeding. A few similar cases have appeared in the literature. The mechanism of pupillary sparing appears to be based on the position of the parasympathetic pupilloconstrictor fibers within the subarachnoid portion of the third nerve and on the anatomic relationship between the third nerve and the junction of the carotid and posterior communicating arteries.