Diffuse and uncontrolled vascular smooth muscle cell proliferation in rapidly progressing pediatric moyamoya disease.

Moyamoya disease is a rare stroke syndrome of unknown etiology resulting from stenosis or occlusion of the supraclinoid internal carotid artery (ICA) in association with an abnormal vascular network in the basal ganglia. Although the highest incidence of moyamoya disease is in pediatric patients, pathology reports have been primarily limited to adult samples and describe occlusive fibrocellular lesions in the intimae of affected arteries. We describe the case of a young girl with primary moyamoya disease who presented at 18 months of age with right hemiparesis following an ischemic stroke. Angiography showed stenosis of the distal left ICA, left middle cerebral artery, and right ICA. An emergent left-sided dural inversion was performed. Recurrent strokes and alternating hemiplegia necessitated a right dural inversion 6 months later. Nonetheless, her aggressive disease proved uniquely refractory to surgical revascularization, and she succumbed to recurrent strokes and neurological deterioration at 2.5 years of age. Pathological specimens revealed a striking bilateral occlusion of the anterior carotid circulation resulting from intimal proliferation of smooth muscle cells (SMCs). Most strikingly, the ascending aorta and the superior mesenteric artery demonstrated similar intimal proliferation, along with SMC proliferation in the media. The systemic pathology involving multiple arteries in this extremely young child, the first case of its kind available for autopsy, suggests that globally uncontrolled SMC proliferation, in the absence of environmental risk factors and likely resulting from an underlying genetic alteration, may be a primary etiologic event leading to moyamoya disease.