Histopathologic and morphometric studies of leptomeningeal vessels in moyamoya disease.

To clarify the morphogenesis of vascular anastomoses in the leptomeninx, we examined the leptomeningeal vessels of six autopsied patients with moyamoya disease who died of cerebral hemorrhage. Sites examined in the brain (the frontal pole, frontoparietal convexity, and lateral occipital region) were selected by the presence of angiographic abnormalities on the convexity of the hemisphere. At all examined sites, neither the vascular density (number of blood vessels per unit length of underlying cortical surface) nor the arterial/venous ratio differed significantly between the patients and 14 controls. All patients showed dilatative changes of both arteries and veins; however, attenuation or disruption of the internal elastic lamina and fibrous intimal thickening were more prominent in those patients who had had moyamoya disease longer. Our results indicate that the leptomeningeal vessels of moyamoya disease are not newly formed but are merely dilated preexisting vessels and that the structural alteration of the vascular walls suggests their adaptability for participation in the collateral circulation at the cerebral surface.