Ruptured artery of Percheron aneurysm in moyamoya disease with thalamic hemorrhage and acute hydrocephalus: illustrative case.

backgroundIn moyamoya disease, fragile collateral networks such as periventricular anastomoses are associated with an increased risk of hemorrhage, particularly in the posterior circulation. Peripheral aneurysms arising from these vessels are rare, and those involving the artery of Percheron are exceptionally uncommon. OBSERVATIONS: A 55-year-old patient with a history of thalamic hemorrhage presented with headache and impaired consciousness. CT revealed a right thalamic hemorrhage with intraventricular extension and acute hydrocephalus. Emergency ventricular drainage was performed. Subsequent angiography identified a ruptured peripheral aneurysm arising from the artery of Percheron originating from the left P1 segment, along with right-dominant moyamoya vascular architecture. The aneurysm was successfully treated with N-butyl cyanoacrylate embolization to prevent rebleeding. Due to insufficient clearance of intraventricular hematoma, endoscopic evacuation was performed. The patient experienced no rebleeding, and follow-up angiography confirmed durable obliteration of the aneurysm. LESSONS: Peripheral aneurysms arising from the artery of Percheron in moyamoya disease are extremely rare but should be considered in cases of deep hemorrhage with intraventricular extension. Prompt endovascular embolization using liquid embolic agents, combined with endoscopic hematoma evacuation, may provide an effective and minimally invasive treatment strategy. https://thejns.org/doi/10.3171/CASE26356.