Twenty two autopsied cases with Moyamoya disease were examined clinicopathologically. Pathologically, fibrosing stenoses or occlusions involved the circle of Willis and its major branches in all cases. In 14 of 20 patients numerous collateral channels, muscular in type, paralleled the circle, bypassing the occluded natural passages. Fresh and massive cerebral hemorrhage was confirmed in 17 and cerebral infarcts in 4 among 22 patients. Among these 17 patients, massive hemorrhage was found in the basal ganglia, thalamus and hypothalamus of 12 patients, and in the thalamus, cerebral peduncle and midbrain of 5 patients. Rupture of dilated small muscular arteries was demonstrated in fresh hemorrhagic lesions in 5, and old hemorrhagic lesions in 1 of the 17 patients. Saccular aneurysm of cerebral arteries in the subarachnoid space was present in 2 of 22 patients. In one patient posterior cerebral-posterior communicating aneurysm was ruptured in the arachnoid space. No rupture involved the perforating arteries in the arachnoid space. These findings suggest that rupture of overgrown perforating arteries as collaterals in brain may be the main cause of single or repeated cerebral hemorrhage in Moyamoya disease.
On the other hand, stenosing lesions were found in perforating arteries. Elastofibrotic thickening of the intima and the media, edematous intimal thickening and luminal narrowing due to organized thrombi were observed. These stenotic lesions are an important factor in the occurrence of cerebral infarcts.
Coronary arteries and renal arteries were examined in 11 patients. In one patient, concentric intimal fibroplasia resembling intimal fibroplasia type of fibromuscular dysplasia caused marked stenoses in coronary and renal arteries. Eccentric fibrous intimal thickening or atheromatous lesions were present at the bifurcation of coronary and renal arteries in majority of adult cases. These findings suggest that systemic arterial involvement including intracranial vessels may exist in Moyamoya disease.
