Diagnosis and management of vertebral artery stenosis.

Introduction Approximately one-quarter of ischaemic strokes involve the posterior or vertebrobasilar circulation. 1,2 Stenosis of the vertebral artery can occur in either its extra-or intracranial portions, and may account for up to 20% of posterior circulation ischaemic strokes. 3–6 Stenotic lesions, particularly at the origin of the vertebral artery, are not uncommon. In an angiographic study of 4748 patients with ischaemic stroke, some degree of proximal extracranial vertebral artery stenosis was seen in 18% of cases on the right and 22.3% on the left. 7 This was the second most common site of stenosis after internal carotid artery stenosis at the carotid bifurcation. Such stenotic lesions are now potentially treatable by endovascular techniques. 8 In marked contrast with carotid artery stenosis, the optimal management of vertebral artery stenosis has received limited attention, and is poorly understood. This partly reflects difficulties in imaging the vertebral artery adequately, and limited surgical treatment options. Recent improvements in imaging and the arrival of vertebral artery angioplasty, however, have opened up new opportunities for intervention in this disease. We review vertebral artery anatomy, what is known of the natural history of vertebral artery disease , the role of imaging in the diagnosis of ver-tebral artery stenosis, and treatments for vertebral artery stenosis. Anatomy The vertebral artery arises from the supraposterior aspect of the first part of the subclavian artery. In 6% of cases, the left vertebral artery arises directly from the aortic arch. Unlike the internal carotid artery, which is an almost direct extension of its parent vessel the common carotid artery, the vertebral artery branches almost at right angles to its feeding vessel. The vertebral artery, being 3–5 mm in diameter, is of much smaller relative calibre than the subclavian, with only a small amount of subclavian blood flow normally being directed into each vertebral. These differences in anatomy may well reflect in dissimilar flow dynamics between the origins of the carotid and vertebrobasilar cerebral circulations, with a consequent predilection to forming a different type of atherosclerotic plaque. Plaque disease at the vertebral artery origin has been thought to be 'smoother' and less prone to ulcerate with secondary thrombus formation. 9 Differences between carotid and vertebral artery plaque morphology have been inferred from angiographic appearances, but there are few published pathological data to support this. 10 Anatomically, the vertebral artery can be divided into three extracranial parts and an intracranial portion (Figure 1). Part …