Because the vertebral arteries in the neck originate from the proximal subclavian arteries, disease of the subclavian or innominate arteries proximal to the vertebral artery origin can cause reduction of vertebral artery flow. SUBCLAVIAN AND INNOMINATE ARTERIES - Atherostenotic lesions of the innominate and subclavian arteries do cause arm ischemia and transient ischemic attacks (TIAs) but seldom cause strokes. Most infarcts in the posterior cerebral artery territory are due to embolism from the heart, aorta, or vertebral arteries. Unlike the vertebral and basilar arteries, atherosclerosis and dissection of the posterior cerebral arteries is not common.Dissection of the extracranial and intracranial vertebral arteries is another frequent cause of ischemia within the posterior circulation.(See "Intracranial large artery atherosclerosis: Epidemiology, clinical manifestations, and diagnosis", section on 'Epidemiology'.) Atherosclerosis of the intracranial vertebral arteries and of the basilar artery is also common. The proximal portion of the vertebral artery in the neck is the most common location of atherosclerotic occlusive disease within the posterior circulation.About one-third of posterior circulation strokes are caused by occlusive disease within the large neck and intracranial arteries, which are the vertebral arteries in the neck and the intracranial vertebral, basilar, and posterior cerebral arteries.Dolichoectasia (elongation and tortuosity) of the vertebral and basilar arteries is another occasional cause. SOURCE OF ISCHEMIA - The most common causes of posterior circulation large artery ischemia are atherosclerosis, embolism, and dissection. (See "Initial assessment and management of acute stroke" and "Approach to reperfusion therapy for acute ischemic stroke" and "Early antithrombotic treatment of acute ischemic stroke and transient ischemic attack".) The evaluation and management of acute ischemic stroke (including stroke involving the posterior circulation) are discussed separately. These arteries are the innominate and subclavian arteries in the chest, the vertebral arteries in the neck, and the intracranial vertebral, basilar, and posterior cerebral arteries. This topic will review the major clinical syndromes associated with posterior circulation ischemia related to stenosis or occlusion of the large aortic arch, neck, and intracranial arteries. INTRODUCTION - Twenty percent of ischemic events in the brain involve posterior circulation (vertebrobasilar) structures.
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