A unique anatomic variant: Left anterior choroidal artery arising proximal to fetal posterior communicating artery.

Anomalous vascular variants pose unique challenges in clinical management, especially in the context of neuroendovascular intervention. We present a case report detailing an extremely rare anatomic variant involving the left anterior choroidal artery, which arises proximal to the fetal posterior communicating artery. Our patient presented with confusion and speech abnormalities following a benzodiazepine overdose. Subsequent computed tomography of the head revealed an aneurysm originating from the left supraclinoid carotid artery. This aneurysm was located 2 mm more proximal to the origin of the left posterior communicating artery and was initially misidentified as originating from the left posterior communicating artery due to its proximity. Further diagnostic cerebral angiography revealed an extremely rare anatomical variant where the left anterior choroidal artery anomalously arose proximal to a fetal posterior communicating artery, with the aneurysm being correctly identified as arising from the left anterior choroidal artery. The patient underwent successful detoxification and has since shown remarkable improvement, with plans for elective endovascular flow diversion treatment under dual antiplatelet therapy. Considering the critical role of the anterior choroidal artery in supplying vital cerebral structures, awareness of such variants is paramount to prevent inadvertent vascular injury and optimize patient outcomes. This case highlights the necessity of meticulous pre-procedural imaging and multidisciplinary collaboration in managing neurovascular anomalies effectively.