Subclavian Steal

Notice on the early image that the left vertebral artery (dashed arrow) is less enhanced than the right vertebral artery and that there is occlusion of the origin of the left subclavian artery (solid arrow) with decreased enhancement of the left subclavian artery. The vertebral arteries originate from the subclavian arteries, so the left vertebral artery is not receiving normal flow because its parent vessel is occluded. In the later phase the occlusion persists (solid arrow) but the vertebral artery and the left subclavian have enhancement very similar to the rest of the arteries. Flow in the left vertebral artery is retrograde, or reversed, in this case. It is "stealing" flow from the right vertebral artery and posterior circulation and sending it downward to the left subclavian artery. Patients with subclavian steal can be asymptomatic, can have symptoms that are elicited with arm exercise (arm claudication) or can have more serious symptoms attributable to verebrobasilar insufficiency such as dizziness, vertigo, drop attacks, vision issues, paresthesias, dysarthria or dysphagia. Rarely they can present with brainstem, cerebellar, or posterior circulation infarct.