Cerebral dissecting aneurysms in patients with moyamoya disease. Report of two cases.

Dissecting intracranial arterial aneurysms were identified in a 16-year-old girl and a 48-year-old man with moyamoya disease. Hemiplegia or tetraplegia rapidly developed. Angiography revealed bilateral stenoses or occlusion of the bifurcation of the internal carotid arteries (ICA's) and an unusual vascular network at the base of the brain. Autopsy confirmed massive hemorrhage from the thalamus and putamen, with intraventricular extension. The intracranial segments of both ICA's were markedly stenotic in both patients, due to eccentric fibroelastic intimal thickening. In one patient, a dissecting aneurysm was identified microscopically, involving the proximal segment of the left anterior cerebral artery. In the other patient, the right middle cerebral artery (MCA) was dissected beneath the internal elastic lamina along the entire length of the horizontal segment of the MCA. Thus, cerebral dissecting aneurysms may be present in patients with moyamoya disease.