Pupil sparing oculomotor nerve paresis after anterior communicating artery aneurysm rupture: False localizing sign or acute microvascular ischemia?

BACKGROUND: We describe a rare case of solitary pupil sparing oculomotor nerve paresis following rupture of anterior communicating artery (ACom) aneurysm and discuss the pertinent literature. Oculomotor nerve paresis caused by an ACom aneurysm rupture is an uncommon occurrence. Also, partial paresis affecting only fibers of superior division of oculomotor nerve is never reported before. CASE DESCRIPTION: A 55-year-old female, known hypertensive presented 5 days after an episode of acute severe headache, with Glasgow Coma Scale (GCS) of E2V2M5, left ptosis, normal pupils, paraparesis, and computed tomography (CT) scan showed diffuse subarachnoid hemorrhage (SAH). CT angiography revealed ACom aneurysm pointing antero-superiorly toward right. Patient later underwent endovascular coiling of the aneurysm. Subsequently there was partial improvement of ptosis in 3 weeks. CONCLUSION: Though pupil sparing oculomotor nerve paresis may not have much localizing value, it helps to understand acute microvascular spasm with potential therapeutic implications.