Circle of Willis

The main sources of blood for the brain are a. carotis interna dextra et sinistra and a. vertebralis dextra et sinistra which together with other vessels create the circle of Willis (circulus arteriosus cerebri). This circle is named after English physician Thomas Willis. The circle is located in the subarachnoideal space - in the area around fossa interpeduncularis, corpora mammillaria and chiasma opticum. It made of five arteries, which connect together through anastomoses. The circle of Willis is not identical in all people. Anomalies appear in up to 50% of cases.

It is created by:

a. carotis comunis dx. et sin. → a. carotis interna dx. et sin. →


 * a. cerebri anterior dx. et sin.
 * a. communicans anterior
 * a. cerebi media dx. et sin.
 * a. communicans posterior dx. et sin.

a. vertebralis → a. basilaris → a. cerebri posterior

The circle of Willis branches into:
 * Cortical arteries, which is generally branching of a. cerebri anterior, media et posterior. They branch into short (cortical) and long (medullary) branches.
 * Aa. centrales, which branch into aa. centrales anteromediales, aa. centrales anterolaterales, aa. centrales posterolaterales.
 * Aa. choroideae – capsula interna, brain stem

The function of the circle of Willis is equalization of pulse waves from afferent vessels and equivalent filling of the artreries leaving the circle. The circle of Willis can partially substitute the function of blood supply to the brain of an afferent artery if it happens to get occluded.

Relevant articles

 * Arteries of the brain
 * Ischemia of the brain