Vertebral artery hypoplasia is associated with a decrease in net vertebral flow volume.

The definition and clinical significance of vertebral artery hypoplasia (VAH) remain inconclusive. VAH has been proposed as a predisposing factor of posterior circulation ischemic stroke. The aim of this study was to determine a best cut-off diameter of vertebral artery (VA) for VAH and to investigate if unilateral VAH is associated with a decrease in net vertebral flow volume. Retrospective data of 1000 presumably healthy subjects free of cerebrovascular disease or apparent carotid atherosclerosis were analysed. We found that a VA diameter </=2.5mm is an ideal value to define VAH. The flow volume of the identified hypoplastic VA was remarkably low and the contralateral VA had only a slightly increased compensatory flow volume. The net VA flow volumes remained significantly and markedly lower in subjects with unilateral VAH (140.7+/-46.2mL/min) than those in subjects without VAH (190.1+/-54.5mL/min, p<0.001). Flow volume insufficiency of VA (defined as a net VA flow volume less than 100mL/min) occurred more frequently in individuals with VAH than in those without VAH (22.1% vs. 2.4%, p<0.001). Our study suggested that asymptomatic subjects with VAH had a significantly lower net VA flow volume and a higher frequency of VA flow insufficiency than the control group. (E-mail: hhhu@vghtpe.gov.tw).