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The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis that supplies blood to the brain and surrounding structures in reptiles, birds and mammals, including humans. [1] It is named after Thomas Willis (1621–1675), an English physician. [2]
Willis was a pioneer in research into the anatomy of the brain, nervous system and muscles. His most notable discovery was the "Circle of Willis", a circle of arteries on the base of the brain. Willis's anatomy of the brain and nerves, as described in his Cerebri anatome of 1664, is minute and elaborate.
In case of narrowing of other arteries of the circle of Willis or the arteries supplying the circle, the anterior communicating artery can provide a way to supply blood to the opposite (affected) side of the circle. This can often preserve the cerebral blood supply well enough to avoid the symptoms of ischemia. [7]
The anterior and posterior circulations meet at the circle of Willis, pictured here, which rests at the top of the brainstem. Inferior view. The posterior cerebral circulation is the blood supply to the posterior portion of the brain, including the occipital lobes, cerebellum and brainstem. It is supplied by the following arteries:
There are many examples of normal arterio-arterial anastomoses in the body. Clinically important examples include: Circle of Willis (in the brain) Coronary: anterior interventricular artery and posterior interventricular artery of the heart; Scapular anastomosis (for the subclavian vessels)
Saccular aneurysms are almost always the result of hereditary weaknesses in blood vessels and typically occur within the arteries of the circle of Willis, [20] [26] in order of frequency affecting the following arteries: [27] Anterior communicating artery; Posterior communicating artery; Middle cerebral artery; Internal carotid artery; Tip of ...
Collateral circulation is the alternate circulation around a blocked artery or vein via another path, such as nearby minor vessels. [1] It may occur via preexisting vascular redundancy (analogous to engineered redundancy), as in the circle of Willis in the brain, or it may occur via new branches formed between adjacent blood vessels (neovascularization), as in the eye after a retinal embolism ...
Partial anterior circulation infarct (PACI) is a type of cerebral infarction affecting part of the anterior circulation supplying one side of the brain.. Partial anterior circulation stroke syndrome (PACS) refers to the symptoms of a patient who clinically appears to have had a partial anterior circulation infarct, but who has not yet had any diagnostic imaging (e.g. CT Scan) to confirm the ...