Circle of Willis

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Willis circle (also called Willis Circle , circle from Willis , cerebral artery circle , and Willis polygon ) is a circulating anastomosis that supplies blood to the brain and surrounding structures. Named after Thomas Willis (1621-1675), a British doctor.

Video Circle of Willis

Structure

The circle of Willis is part of the cerebral circulation and consists of the following arteries:

• The anterior cerebral artery (left and right)
• Anterior communicates arteries
• Internal carotid artery (left and right)
• Posterior cerebral artery (left and right)
• Posterior communicative artery (left and right)

The central cerebral artery, supplying the brain, is not considered part of the circle.

Arterial origin

The left and right internal carotid arteries arise from the common left and right carotid arteries.

The posterior communicative artery is released as a branch of the internal carotid artery before it is divided into terminal branches - the anterior and middle cerebral arteries. The anterior cerebral artery forms the anterolateral part of the Willis circle, whereas the cerebral artery of the media does not contribute to the circle.

The right and left posterior cerebral arteries arise from the basilar artery, which is formed by the left and right vertebral arteries. The vertebral artery emerges from the subclavian artery.

The anterior communication arteries connect two anterior cerebral arteries and can be said to arise either from the left or right side.

All the involved arteries secrete cortical and central branches. The central branches supply the inside of the Willis circle, more specifically, the Interpeduncular fossa. The cortical branches are named for the area they supply. Since they do not directly affect the Willis circle, they are not addressed here.

Variations

Sufficient anatomical variation is present in the Willis circle. Based on a study of 1413 brains, the classical anatomy of the circle was seen only in 34.5% of cases. In one general variation the proximal portion of the posterior cerebral artery is narrow and the posterior ipsilateral communicative artery is large, so the internal carotid artery supplies the posterior cerebrum. In another variation the anterior communications artery is a large vessel, so a single internal carotid supplies both anterior cerebral arteries.

Maps Circle of Willis

Function

The arrangement of the brain arteries into the circle of Willis creates redundancy (analogous to engineered redundancy) for the collateral circulation in the cerebral circulation. If one part of the circle becomes blocked or stenosed or one of the arteries supplying the circle is obstructed or narrowed, blood flow from other blood vessels can often retain cerebral perfusion well enough to avoid ischemic symptoms.

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Clinical interests

Aneurysms

Subclavian stealing syndrome

Redundancy introduced by the Willis circle can also lead to reduced cerebral perfusion. In subclavian steal syndrome, blood is "stolen" from the Willis circle to maintain blood flow to the upper limb. Subclavian steal syndrome results from proximal stenosis (narrowing) of the subclavian artery, an artery supplied by the aorta which is also the same blood vessel that eventually feeds the Willis circle through the vertebral artery.

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Additional images

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References

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See also

• Cerebral circulation
• Leptomeningeal collateral circulation

Source of the article : Wikipedia