Circle of Willis 244346 222456459 2008-06-29T12:48:29Z DOI bot 6652755 Citation maintenance. Added: author, year. Formatted: title, volume, pages. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Infobox Artery | Name = {{PAGENAME}} | Latin = circulus arteriosus cerebri | GraySubject = 147 | GrayPage = 574 | Width = 335<!--omit "px" or image will fill page--> | Image = Circle of Willis en.svg | Caption = Schematic representation of the '''circle of Willis''', arteries of the brain and [[brain stem]]. | Image2 = Arteries_beneath_brain_Gray_closer.jpg | Caption2 = The [[brain]] and arteries at base of the brain. Circle of Willis is formed near center. The [[temporal lobe|temporal]] pole of the [[cerebrum]] and a portion of the [[cerebellum|cerebellar]] hemisphere have been removed on the right side. Inferior aspect (viewed from below). | BranchFrom = | BranchTo = | Vein = | Supplies = | MeshName = Circle+of+Willis | MeshNumber = A07.231.114.228.351 }} The '''circle of Willis''' (also called the '''cerebral arterial circle''' or '''arterial circle of Willis''') is a circle of [[artery|arteries]] that supply blood to the [[brain]]. It is named after [[Thomas Willis]] ([[1621]]-[[1673]]), an [[England|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. [http://journals.tubitak.gov.tr/medical/issues/sag-04-34-4/sag-34-4-9-0402-10.pdf Free Full Text].</ref> ==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 one part of the circle becomes blocked or narrowed ([[stenosis|stenosed]]) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other [[blood vessel]]s can often preserve the cerebral perfusion well enough to avoid the symptoms of [[ischemia]].<ref>{{cite journal | author = Boorder, Michiel J.| title = Spect measurements of regional cerebral perfusion and carbondioxide reactivity: Correlation with cerebral collaterals in internal carotid artery occlusive disease | journal = J Neurol | volume = 253| issue = | pages = 1285| year = 2006| pmid = 17063318| doi = 10.1007/s00415-006-0192-1}}</ref> ==Anatomic variation== Considerable [[anatomic variation]] exists in the circle of Willis. Based on a study of 1413 brains, the "textbook version" of the circle is only seen in 34.5% of cases.<ref>Bergman RA, Afifi AK, Miyauchi R, Circle of Willis. [http://www.vh.org/adult/provider/anatomy/AnatomicVariants/AnatomyHP.html Illustrated Encyclopedia of Human Anatomic Variation], URL: [http://www.anatomyatlases.org/AnatomicVariants/Cardiovascular/Text/Arteries/CircleofWillis.shtml http://www.anatomyatlases.org/AnatomicVariants/Cardiovascular/Text/Arteries/CircleofWillis.shtml]. Accessed on November 6, 2005.</ref> In one common variation the proximal part of the [[posterior cerebral artery]] is narrow and its ipsilateral [[posterior communicating artery]] is large, so the [[internal carotid artery]] supplies the posterior cerebrum. In another variation the anterior communicating artery is a large vessel, such that a single internal carotid supplies both anterior cerebral arteries. ==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 is supplied by the same vessel (the [[Aorta]]) that eventually feeds the circle of Willis via the [[Common carotid artery]]), blood is "stolen" from the circle of Willis to preserve blood flow to the [[upper limb]]. ==Origin of arteries== [[Image:Cerebral angiography, arteria vertebralis sinister injection.JPG|right|thumb|250px|Cerebral angiogram showing a anterior/posterior projection of the [[vertebral artery|vertebro]][[basilar artery|basilar]] and [[posterior cerebral]] circulation, i.e. the posterior aspect of the circle of Willis and one of its feeding vessels.]] The left and right internal carotid arteries arise from the right and left [[common carotid artery|common carotid arteries]]. The posterior communicating artery is given off as a branch of the internal carotid artery just before it divides into its terminal branches - the anterior and middle cerebral arteries. The anterior cerebral artery forms the anterolateral portion of the Circle of Willis, while the middle cerebral artery does not contribute to the Circle. The right and left [[posterior cerebral artery|posterior cerebral arteries]] arise from the [[basilar artery]], which is formed by the left and right [[vertebral artery|vertebral arteries]]. The [[vertebral artery|vertebral arteries]] arise from the [[subclavian artery|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. All arteries involved give off cortical and central branches. The central branches supply the interior of the Circle of Willis, more specifically, the Interpeduncular fossa. The cortical branches are named for the area they supply. Since they do not directly affect the Circle of Willis, they are not dealt with here. ==References== {{reflist|2}} {{Arteries of head and neck}} [[Category:Arteries]] [[Category:Head and neck]] [[da:Circulus arteriosus cerebri]] [[de:Circulus arteriosus cerebri]] [[es:Polígono de Willis]] [[fr:Polygone de Willis]] [[it:Poligono di Willis]] [[la:Circulus arteriosus cerebri]] [[nl:Cirkel van Willis]] [[no:Willis' arterielle sirkel]] [[nds:Circulus arteriosus cerebri]] [[pl:Koło tętnicze mózgu]] [[pt:Círculo arterial cerebral]] [[fi:Aivojen valtimokehä]]