title: Hemodynamic impact of fetal-variant Willisian circle on cerebral circulation: a duplex ultrasonography study.
abstract: OBJECTIVE
  The Willisian circle can redistribute the vertebrobasilar flow and the reduction of flow is attributable to orthrostatic presyncope. To evaluate this hemodynamic aspect, we investigated anterior and posterior cerebral blood flow (CBF) volume distributions according to the variation of the Willisian circle, and compared those between controls and patients with presyncope.
  
  
  METHODS
  Subjects underwent cerebral CT angiography and color-coded duplex sonography measuring flow volumes of the internal carotid artery (ICAs) and vertebral artery (VAs). According to clinical manifestations and Willisian configurations, CBF volume patterns were analyzed.
  
  
  RESULTS
  Between the presyncope (n = 25) and control groups (n = 76), the prevalence of fetal-variant Willisian configuration (48% vs. 21%, p = 0.004) and posterior CBF volume (126 ± 85 vs. 165 ± 64 ml/min, p = 0.015) was significantly different, but A1 morphology, anterior CBF, and total CBF volumes were not. Total CBF volume was 769 ± 176 ml/min (80% ICAs and 20% VAs). The posterior CBF volume lowered significantly (172 ± 70 vs. 122 ± 62 vs. 92 ± 44 ml/min; p < 0.001) toward the two-sided fetal type variation, although total CBF volume is similar among the three groups (p = 0.742).
  
  
  CONCLUSIONS
  The present study suggests that Willisian configuration contributes to orthostatic presyncope and flow distribution of the cerebral circulation.
authors: Department of Neurology, Ajou University School of Medicine, Suwon, Kyunggi-do, South Korea. dacda@hanmail.net
authors: Ji Man
authors: JM
authors: Hong
authors: Jin Soo
authors: JS
authors: Lee
authors: Dong Hoon
authors: DH
authors: Shin
authors: Seok Woo
authors: SW
authors: Yong