Background: Spontaneous middle cerebral artery occlusion associated with moyamoya phenomenon is distinct from moyamoya disease. The hemodynamic stress on the collateral channel occasionally leads to aneurysm formation, which may manifest as hemorrhage. The etiology of this disease has not been fully understood.
Case description: A 63-year-old woman presented with left putaminal hemorrhage. The cerebral angiogram revealed a significant stenosis in the proximal segment of the left middle cerebral artery. Collateral arteries originating from the horizontal segment of the ipsilateral anterior cerebral artery and the ambient segment of the ipsilateral posterior cerebral artery supplied the middle cerebral artery distal to the stenosis. Both of the collateral channels had associated aneurysms that were surgically obliterated. The aneurysm on the collateral artery from the posterior cerebral artery was responsible for the putaminal hemorrhage.
Conclusions: Spontaneous middle cerebral artery occlusion may lead to focal moyamoya phenomenon and aneurysmal intracerebral, intraventricular, or subarachnoid hemorrhage. The presence of a co-existing anomalous collateral artery in the present case suggests a congenital etiology of the focal middle cerebral artery occlusion.