Circle of Willis
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- There is also a band by this name, see Circle of Willis (band).
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 English physician.<ref>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.</ref>
Contents |
Components
- Anterior cerebral artery (left and right)
- Anterior communicating artery
- Internal carotid artery (left and right)
- Posterior cerebral artery (left and right)
- Posterior communicating artery (left and right)
The basilar artery and middle cerebral arteries, though they supply the brain, are not considered part of the circle.<ref>Moore KL, Dalley AR. Clinically Oriented Anatomy, 4th Ed., Lippincott Williams & Wilkins, Toronto. Copyright 1999. ISBN 0-683-06141-0.</ref>
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.
Anatomic variation
Considerable anatomic variation exists in the circle of Willis. The "textbook version" of the circle, based on a series of 1413 brains, is only seen in 34.5% of cases.<ref>Bergman RA, Afifi AK, Miyauchi R, Circle of Willis. Illustrated Encyclopedia of Human Anatomic Variation, URL: http://www.anatomyatlases.org/AnatomicVariants/Cardiovascular/Text/Arteries/CircleofWillis.shtml. Accessed on November 6, 2005.</ref>
Subclavian steal and the circle of Willis
The redundancies that the circle of Willis introduce can also lead to reduced cerebral perfusion.<ref>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.</ref><ref>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.</ref> In subclavian steal syndrome, which results from a proximal stenosis (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 perserve 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.
The anterior cerebral arteries and posterior communicating arteries arise from the internal carotid arteries' trifurcations.
The right and left posterior cerebral arteries arise from the basilar artery, which is formed by the left and right vertebral arteries. The vertebral arteries arise from the subclavian arteries.
The anterior communicating artery connects the two anterior cerebral arteries and could be said to arise from either the left or right side.
References
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External links
- Variations of Circle of Willis and Related Vessels - Illustrated Encyclopedia of Human Anatomic Variation
- Picture of the Circle of Willis (cadaver) - North Harris College
Template:BloodVesselsde:Circulus arteriosus cerebri fr:Polygone de Willis