Subclavian steal despite ipsilateral vertebral occlusion.

In the classic subclavian steal syndrome, vertebrobasilar insufficiency is caused by reverse flow in the vertebral artery ipsilateral to a subclavian stenosis or occlusion. We present two patients with vertebrobasilar insufficiency and ipsilateral vertebral and subclavian occlusive disease. The postulated mechanism of vertebrobasilar insufficiency is reverse flow in collateral neck vessels. In both patients, symptoms were relieved by carotid subclavian bypass. Thus, vertebral occlusion ipsilateral to a subclavian stenosis does not preclude subclavian steal syndrome.