Microsurgical clipping for the true posterior communicating artery aneurysm in the distal portion of the posterior communicating artery

BACKGROUND Aneurysms arising from the posterior communicating artery (PCoA) itself are rare in which aneurysms usually located in the proximal portion of the PCoA. The authors report a case of the true PCoA ruptured aneurysm in the distal portion of the PCoA. CASE DESCRIPTION The patient was an 83-year-old man who suffered subarachnoid hemorrhage. Cerebral angiography revealed a saccular aneurysm arising on the fetal type right PCoA itself in the distal portion of the PCoA. 2 days after the onset of symptoms, the patient underwent right interfascial pterional craniotomy, with anterior temporal approach. The aneurysm was successfully clipped with the preservation of both the PCoA and the thalamoperforating artery. CONCLUSION We speculated that blood flow into the PCoA gradually increased after occlusion of the left vertebral artery, which induced tortuosity of the PCoA. As a result, hemodynamic stress might increase near the curvature and cause aneurysm formation.