Intracranial aneurysms with superior division paresis of the oculomotor nerve.

Five patients with intracranial aneurysms had unilateral ptosis, limitation of supraduction, and normal pupillary reactivity. The most common aneurysm location for superior division paresis of the oculomotor nerve was the superior cerebellar-posterior cerebral artery junction, where aneurysms (3) of the basilar artery compressed and flattened the interpeduncular oculomotor nerve from below. A superior cerebellar artery aneurysm and brain stem infarction affected the intra-axial course of the oculomotor nerve producing superior division paresis. Only an aneurysm of the intracavernous carotid artery resulted in superior division paresis at the expected anatomic site of bifurcation of the oculomotor nerve into its superior and inferior divisions. Because the superior division supplies innervation exclusively to the superior rectus muscle and levator palpebrae, an aneurysm involving this branch does not affect the pupillo-constrictor fibers. Consequently, cerebral angiography should be considered in the initial evaluation of this ocular motor deficit.