Circle of Willis is the joining area of several arteries at the bottom (inferior) side of the brain. At the Circle of Willis, the internal carotid arteries branch into smaller arteries that supply oxygenated blood to over 80% of the cerebrum. Blockage of blood flow to the brain for even a short period of time can be disastrous and cause brain damage or even death.
Stroke is the loss of brain function due to blocked blood circulation to the brain. Strokes may be caused by an uncommon type of narrowing, obstruction, or leak in the lining of the carotid artery. This leaking of blood into the artery wall (dissection) may cause a clot to form, reducing blood flow and raising the risk of stroke. The leak may arise from an injury to the neck, which means strokes caused by carotid dissection may occur in young people as well as older people.