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.
Brain Aneurysm Imaging: T1-weighted magnetic resonance image (MRI) of a middle-aged woman with progressive headaches, aphasia, and right-sided hemiparesis. A large intracerebral mass with a significant amount of surrounding edema is depicted. The lesion is a giant internal carotid artery aneurysm.