Spontaneous occlusion of the circle of Willis (moyamoya syndrome).

Three young autopsy and four temporal artery biopsy cases with an arteriographically typical moyamoya syndrome were studied by histologic, electron microscopic, and immunofluorescence methods. In all autopsy cases the intracranial segment of the internal carotid arteries showed concentric intimal thickening with severe stenosis or obstruction of the lumen, folding of the internal elastic lamina, and shrinkage of the external diameter of the vessel. Inflammatory infiltration was absent. Abnormal networks of thin-walled vessels, interpreted as secondary collaterals, were seen at the base and on the convexity of the brain. Degenerative changes, including a ruptured coronary aneurysm in one case, were also noted in the coronary and temporal arteries. In both the intra- and extracranial arteries repeated endothelial damage was indicated by the presence of redundant subendothelial basement membrane-like material. Lipid or calcium deposits were exceptional, and no evidence for the presence of immunoglobulins or components of the complement could be obtained by immunofluorescence. These pathologic alterations, distinct from atherosclerosis, fibromuscular dysplasia, and the established types of arteritis, seem to be identical in children and adults, in spite of different clinical manifestations of the moyamoya syndrome in these age groups. We suggest that a humoral factor, associated with infections, may induce repeated endothelial damage and intimal thickening in the intracranial arteries of genetically predisposed children in analogy with recent observations made in the coronary arteries of young subjects.