Aneurysm at an Extremely Proximal Posterior Communicating Artery Origin Treated With Flow Diverter-Assisted Coiling: A Case Report.

The posterior communicating artery (Pcom) arises from the supraclinoid internal carotid artery (ICA), just proximal to the anterior choroidal artery. Although caliber variations of the Pcom are common, marked proximal displacement of its origin is extremely rare. We report a case of an aneurysm initially diagnosed as a paraclinoid ICA aneurysm that was subsequently identified as a branch-incorporated internal carotid-posterior communicating artery (IC-PC) aneurysm associated with an aberrant Pcom arising from the ICA siphon proximal to the ophthalmic artery. A man in his 60s underwent magnetic resonance imaging/magnetic resonance angiography for headache evaluation, which revealed a 7.5-mm saccular aneurysm in the left paraclinoid ICA. Digital subtraction angiography and three-dimensional rotational angiography demonstrated that a branch arising from the aneurysm base coursed posteriorly and continued to the P1/P2 segment of the posterior cerebral artery. An Allcock test confirmed retrograde opacification of this vessel and the aneurysm from the posterior circulation. These findings established the diagnosis of an aneurysm incorporating an extremely proximal Pcom rather than a simple paraclinoid ICA aneurysm. Because another aneurysm with an irregular shape was also present at the ipsilateral ICA-anterior choroidal artery junction, flow diversion was selected to treat both lesions simultaneously. After dual antiplatelet therapy, Pipeline Flex placement with adjunctive coil embolization was performed successfully. The postoperative course was uneventful. Follow-up magnetic resonance angiography at six months showed complete disappearance of the intra-aneurysmal signal. This case highlights the importance of meticulous preoperative vascular assessment in distinguishing rare branch-incorporated aneurysms from paraclinoid ICA aneurysms and in planning safe endovascular treatment.