Mechanism of stroke. Strokes were classified as: 1)strokes attributable to pre-defined atherosclerotic lesions
(atherosclerotic strokes); and 2)strokes arising from other causes (other strokes).Atherosclerotic stroke was defined as an ischemic stroke occurring in a vascular territory that had stenosis (>=50%) demonstrated on pre-operative MRA. In such patients, ischemic stroke was regarded as directly related to the underlying atherosclerotic lesion. Patients with an ischemic lesion outside the territory of a pre-existing steno-occlusive artery were defined as having other strokes.