CAMRT Radiography Practice Exam

Which of the following arteries is NOT part of the Circle of Willis?

1. Right and left internal carotid arteries

2. Right and left anterior cerebral arteries

3. Anterior communicating artery

4. Right and left vertebral arteries

The correct answer is: Right and left vertebral arteries

The Circle of Willis is a critical arterial structure located at the base of the brain that provides collateral circulation to ensure a consistent blood supply in the event of an occlusion or blockage in one of the major cerebral arteries. The components of the Circle of Willis include the right and left internal carotid arteries, the right and left anterior cerebral arteries, the anterior communicating artery, and the right and left posterior cerebral arteries along with the posterior communicating arteries. The right and left vertebral arteries, however, do not contribute to the Circle of Willis itself. Instead, they provide blood supply to the posterior aspects of the brain. They converge to form the basilar artery, which then branches off into the posterior cerebral arteries that are part of the Circle of Willis. This distinction is crucial; while vertebral arteries are essential for brain perfusion, they are positioned outside the Circle of Willis structure and therefore do not form part of it.