Five aneurysms in the posterior circulation associated with moyamoya disease: illustrative case.

backgroundThe prevalence of aneurysm formation in adults with moyamoya disease (MMD) is higher than that in the general population. The treatment strategy is often individualized based on the patient's disease characteristics. OBSERVATIONS: The authors report the case of a man who presented with an intraparenchymal hemorrhage. Cerebral angiography showed a typical MMD pattern characterized by occlusion and severe stenosis at the terminal portions of the bilateral internal carotid arteries, accompanied by moyamoya-like vasodilation. The bilateral posterior cerebral arteries (PCAs) had collateral blood supply to the anterior circulation, and 5 aneurysms were observed, which is rare. Considering that revascularization through bypass surgery could alter the hemodynamic stresses associated with MMD, the authors performed bilateral extracranial-intracranial bypass surgeries to reconstruct the anterior circulation and reduce the blood flow burden on the vertebrobasilar system. Follow-up imaging demonstrated improved cerebral perfusion in both hemispheres. Importantly, 3 of the 5 aneurysms remained stable, 1 aneurysm had shrunk, and the other had completely resolved. LESSONS: For stable patients with cerebral hemorrhage, CT angiography is recommended before treatment. In surgery of patients with MMD-associated hemorrhage, avoid using artificial dura mater as it can hinder external carotid circulation and complicate future bypass procedures. https://thejns.org/doi/10.3171/CASE24848.