Pathology of so-called "spontaneous occlusion of the circle of Willis".

Abnormal cerebral vascular networks (Moyamoya blood vessels) are now recognized on cerebral angiograms as collaterals caused by chronic obstruction of the internal carotid arteries due to various conditions. After exclusion of cases in which the etiology is clear, there still remain a considerable number of cases characterized by bilateral involvement of the terminal portions of the internal carotid arteries, and by onset at early childhood due to unknown etiology. These cases should be called "spontaneous occlusion of the circle of Willis." This entity is a part of the "Moyamoya" syndrome. Further investigation is necessary to elucidate the exact cause of this entity.