The circle of Willis (also called the cerebral arterial circle, arterial circle of Willis, or circulus arteriosus cerebri) is a circle of arteries that supply the brain. It is named after Thomas Willis (1621-1673), an Englishphysician.Uston C. Dr. Thomas Willis' famous eponym: the circle of Willis. J Hist Neurosci. 2005 Mar;14(1):16-21. PMID 15804755. [Free Full Text].
The basilar artery and middle cerebral arteries, though they supply the brain, are not considered part of the circle.Moore KL, Dalley AR. Clinically Oriented Anatomy, 4th Ed., Lippincott Williams & Wilkins, Toronto. Copyright 1999. ISBN 0-683-06141-0.
Physiologic significance
The arrangement of the brain's arteries into the Circle of Willis creates redundancies in the cerebral circulation. If any one of the arteries in the circle become blocked or narrowed (stenosed) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other blood vessels can usually maintain cerebral perfusion.
The redundancies that the circle of Willis introduce can also lead to reduced cerebral perfusion.Klingelhofer J, Conrad B, Benecke R, Frank B. Transcranial Doppler ultrasonography of carotid-basilar collateral circulation in subclavian steal. Stroke. 1988 Aug;19(8):1036-42. PMID 3041649.Lord RS, Adar R, Stein RL. Contribution of the circle of Willis to the subclavian steal syndrome. Circulation. 1969 Dec;40(6):871-8. PMID 5377222. In subclavian steal syndrome, which results from a proximalstenosis (narrowing) of the subclavian artery (a vessel that supplies a vessel that feeds the circle of Willis), blood is "stolen" from the circle of Willis to preserve blood flow to the upper limb.
Origin of arteries
The left and right internal carotid arteries arise from the right and left common carotid arteries.
