Paradoxical association of moyamoya syndrome with large middle cerebral artery aneurysm and subarachnoid hemorrhage

A 69-year-old woman was admitted to our hospital because of fluctuating dysarthria during the past 2 months. Magnetic resonance imaging revealed old cerebral infarction of the left cerebral hemisphere with acute subarachnoid hemorrhage in the left sylvian fissure. Cerebral angiography showed a large saccular aneurysm, 14 mm in diameter, at the bifurcation of the left middle cerebral artery (MCA) in association with moyamoya vasculopathy with atherosclerosis, including steno-occlusive changes at the bilateral terminal internal carotid arteries and abnormal net-like vessels at the base of the brain. She underwent microsurgical neck clipping of the large aneurysm followed by superficial temporal artery- MCA anastomosis without complication. Intraoperative findings showed no evidence of aneurysm rupture, suggesting that the subarachnoid hemorrhage was due to the intrinsic pathology of moyamoya vasculopathy. The postoperative course was uneventful, and the patient was discharged without neurological deficit. Association of moyamoya syndrome with large MCA aneurysm is extremely rare, and formation of large aneurysm at the vascular territory of an occluded vessel is apparently unique.