Oculomotor nerve palsy caused by arterial displacement due to subarachnoid hemorrhage from a ruptured duplicated middle cerebral artery aneurysm: illustrative case.

BACKGROUND: A duplicated middle cerebral artery (DMCA) is a rare variant of the middle cerebral artery (MCA), arising between the anterior choroidal artery and distal end of the internal carotid artery. Despite its rarity, DMCA is clinically significant due to its association with aneurysm formation and high risk of rupture. No case of oculomotor nerve palsy related to DMCA aneurysm has been reported.

OBSERVATIONS: A 49-year-old woman presented with sudden severe headache (Hunt and Kosnik grade III) and left pupil dilation. Imaging showed a diffuse, left predominant subarachnoid hemorrhage and four aneurysms. Based on the hematoma location and clinical findings, the left DMCA aneurysm was suspected as the rupture point. She underwent left frontotemporal craniotomy with clipping of three aneurysms. Intraoperative evaluation revealed that the DMCA was displaced by perianeurysmal hematoma, compressing the left oculomotor nerve. After aneurysmal neck clipping, removal of the hematoma surrounding the DMCA was performed. Her postoperative course was uneventful and left pupillary dilation returned to normal within a few days postoperatively.

LESSONS: This case demonstrates that a hematoma from a ruptured DMCA aneurysm can displace the DMCA and cause oculomotor nerve palsy. Hence, DMCA aneurysm should be recognized as one of the possible causes of oculomotor nerve palsy. https://thejns.org/doi/abs/10.3171/CASE25651.