The polygon of Willis is a system of arteries, schematically shaped like a circle. It ensures the vascularization (thus the oxygenation) of the brain. This arterial circle is located in the center of the brain/skull. The polygon of Willis has the particularity of linking the different arteries reaching the brain, namely the carotid arteries and the vertebro-basilar system. This anastomosis system allows the brain to receive blood even if one of the arteries of the neck is stenotic.
The Willis polygon is composed of:
It is well demonstrated in magnetic resonance imaging (MRI) by the time-of-flight technique. Reconstructions obtained by the maximum intensity projection (MIP) technique provide images that resemble those obtained by catheter angiography. The images can be rotated in all directions and overprojections can be avoided, clearing each arterial segment.