The subclavian steal phenomenon: a common vascular disorder with rare neurologic deficits.

Three hundred twenty-four patients with reversed vertebral artery blood flow were reviewed for cerebrovascular events. Neither the presence nor the type of vertebral artery steal (permanent, n = 204; intermediate, n = 120) determined neurologic symptoms, which rather were related to coincidental carotid obstructions or abnormal flow velocity patterns in the basilar artery. Most patients (n = 209; 64%) had no neurologic symptoms. Hemispheric events (n = 99; 31%) occurred most frequently in patients with additional carotid lesions and nonhemispheric events in a few patients (n = 16; 5%) often with bilateral vertebral steal. Intracranial Doppler studies from the vertebral and basilar arteries excluded spontaneous retrograde basilar artery perfusion in any of a subgroup of 50 patients examined in addition. Thus, blood flow reversal in extracranial arteries is a marker for atherosclerotic vascular disease in general, rather than an indicator of a patient's risk to develop cerebrovascular events from hemodynamic insufficiency in the territory affected. Surgical treatment is discouraged for most patients with this benign flow abnormality.