Mechanism of moyamoya vessels secondary to intracranial atherosclerotic disease: angiographic findings in patients with middle cerebral artery occlusion.

Moyamoya vessels, which form a fragile collateral vascular network at the base of the brain, are associated with moyamoya disease and moyamoya syndrome. The mechanisms involved in their development remain unknown. This study evaluated the angiographic findings of the collateral vasculature in patients with moyamoya vessels secondary to atherosclerotic middle cerebral artery (MCA) occlusion. The study population comprised 26 patients with chronic atherosclerotic unilateral MCA occlusion who underwent digital subtraction angiography. We evaluated the presence of moyamoya vessels and intracranial arterial lesions and the degree of leptomeningeal anastomosis. We divided the patients into two groups, those with and those without moyamoya vessels, and compared clinical backgrounds and angiographic findings between the groups. Of the 26 patients, 17 had moyamoya vessels. The presence of moyamoya vessels was associated with ipsilateral or contralateral anterior cerebral artery stenosis to the occluded MCA (P = .004) and poor development of anterior leptomeningeal anastomosis (P = .012). It also was associated with vascular lesions involving more than one intracranial branch vessel in patients with moyamoya syndrome secondary to atherosclerosis. Our findings suggest that moyamoya vessels might be compensatory collateral vessels associated with poorly developed leptomeningeal collateral vessels.