The fetal variant of the circle of Willis and its influence on the cerebral collateral circulation

Cerebrovasc Dis. 2006;22(4):217-24. doi: 10.1159/000094007. Epub 2006 Jun 20.


In a fetal-type posterior circle of Willis (FTP) there is an embryonic derivation of the posterior cerebral artery (PCA) from the internal carotid artery (ICA). Besides the fact that a larger area is thus dependent on the ICA, leptomeningeal vessels cannot develop between the anterior and posterior circulation. The tentorium namely prevents cerebellar vessels from connecting to the PCA territory. Therefore patients with an FTP could be more prone to develop vascular insufficiency. An overview of the literature is given. We propose to define a partial FTP, in which a small P1 segment between the basilar artery and the postcommunicating part of the PCA is present, and a full FTP, in which the P1 segment is absent. Whether a full FTP is a risk factor for stroke should be subject of further investigation.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Aged
  • Brain / blood supply*
  • Carotid Artery, Internal / abnormalities*
  • Carotid Artery, Internal / physiopathology
  • Central Nervous System Vascular Malformations / complications*
  • Central Nervous System Vascular Malformations / epidemiology
  • Central Nervous System Vascular Malformations / physiopathology
  • Cerebrovascular Circulation*
  • Circle of Willis / abnormalities*
  • Circle of Willis / physiopathology
  • Collateral Circulation*
  • Humans
  • Male
  • Middle Aged
  • Posterior Cerebral Artery / abnormalities*
  • Posterior Cerebral Artery / physiopathology
  • Prevalence
  • Risk Factors
  • Stroke / etiology*
  • Stroke / physiopathology