Histopathological studies on spontaneous occlusion of the circle of Willis (cerebrovascular Moyamoya disease)

Spontaneous occlusion of the circle of Willis (cerebrovascular Moyamoya disease; SOCW) was first described by Japanese surgeons and is thought to have a high incidence in the Japanese population. SOCW is characterized by the angiographical findings of the obstructive vascular lesions around the terminal portions of the internal carotid arteries and the formation of abnormal vascular networks visualized in the arterial phase without any definite underlying conditions. Here, we present a detailed histopathological observation of 31 autopsy cases with SOCW to discuss its etiology which is still a matter of dispute. The obstructive vascular lesion around the terminal portions of the internal carotid arteries which is thought to be the primary site affected in SOCW is due to multilayered eccentric intimal fibrous thickening suggestive of organized mural thrombi. In fact, we found thrombotic lesions frequently in the major cerebral arteries, including those of the circle of Willis, of autopsy cases with SOCW. This fact supports the idea that thrombi play an important role in establishment of the vascular lesions. Extracranial vessels are also shown to be involved and it is conceivable that the systemic etiologic factor, such as the systemic background to form thrombi, exists in patients with SOCW.