Incidence and prognosis of > or = 50% symptomatic vertebral or basilar artery stenosis: prospective population-based study.

The higher risk of early recurrent stroke after posterior circulation transient ischaemic attack or minor stroke versus after carotid territory events could be due to a greater prevalence of large artery stenosis, but there have been few imaging studies, and the prognostic significance of such stenoses is uncertain. Reliable data are necessary to determine the feasibility of trials of angioplasty and stenting and to inform imaging strategies. In the first-ever population-based study, we determined the prevalence of > or = 50% apparently symptomatic vertebral and basilar stenosis using contrast-enhanced MRA in consecutive patients, irrespective of age, presenting with posterior circulation transient ischaemic attack or minor ischaemic stroke in the Oxford Vascular Study and related this to the 90-day risk of recurrent transient ischaemic attack and stroke. For comparison, we also determined the prevalence of > or = 50% apparently symptomatic carotid stenosis on ultrasound imaging in consecutive patients with carotid territory events. Of 538 consecutive patients, 141/151 (93%) had posterior circulation events and had vertebral and basilar imaging, of whom 37 (26.2%) had > or = 50% vertebral and basilar stenosis, compared with 41 (11.5%) patients with > or = 50% ipsilateral carotid stenosis in 357/387 (92%) patients with carotid events who had carotid imaging (OR = 2.74; 95% CI = 1.67-4.51; P = 0.002). Presence of > or = 50% vertebral and basilar stenosis was unrelated to age, sex or vascular risk factors and, in contrast to > or = 50% carotid stenosis was not associated with evidence of coronary/peripheral atherosclerosis. In patients with posterior circulation events, > or = 50% vertebral and basilar stenosis was associated multiple transient ischaemic attacks at presentation (22% versus 3%; OR = 9.29; 95% CI = 2.31-37.27; P < 0.001) and with a significantly higher 90-day risk of recurrent events (OR = 3.2; 95% CI = 1.4-7.0; P = 0.006), reaching 22% for stroke and 46% for transient ischaemic attack and stroke. The prevalence of > or = 50% vertebral and basilar stenosis in posterior circulation transient ischaemic attack or minor stroke is greater than the prevalence of > or = 50% carotid stenosis in carotid territory events, and is associated with multiple transient ischaemic attacks at presentation and a high early risk of recurrent stroke. Trials of interventional treatment are therefore likely to be feasible, but more data are required on the long-term risk of stroke on best medical treatment.