A ruptured aneurysm located at a collateral artery that extended from the proximal A2 segment to the M1 segment, associated with an anomalous branch of the anterior choroidal artery and middle cerebral artery hypoplasia: case report.

We here describe the first case of a ruptured aneurysm located at a collateral artery that extended from the proximal A2 segment to the M1 segment, which was associated with an anomalous branch of the anterior choroidal artery and middle cerebral artery (MCA) hypoplasia. The aneurysm was revealed by angiograms and intraoperative findings. No previous accounts have been published of such an extremely rare vessel anomaly. In practice, this case highlights the urgent need to preoperatively recognize such vascular anomalies, as well as to better understand the collateral blood supply in cerebral ischemia associated with these MCA anomalies. Such knowledge will be helpful for planning optimal surgical procedures.