What percentage of people have a complete circle of Willis?

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Explore the Hemispheres 3.0 Level I Brain Anatomy and Physiology Test. Study with detailed questions, answers, and hints. Enhance your knowledge and boost your preparation for success!

Multiple Choice

What percentage of people have a complete circle of Willis?

Explanation:
Completeness of the Circle of Willis varies among people, and a fully connected ring is relatively uncommon. In about one-fifth to one-quarter of individuals, all the major arteries form a complete circle, roughly 20–25%. This is because the posterior communicating arteries and other connections are often hypoplastic or absent in many people, leading to an incomplete circle. The other percentage ranges are not consistent with anatomical studies: 5–10% is too low, while 50–60% and 75–85% are too high to reflect real variation.

Completeness of the Circle of Willis varies among people, and a fully connected ring is relatively uncommon. In about one-fifth to one-quarter of individuals, all the major arteries form a complete circle, roughly 20–25%. This is because the posterior communicating arteries and other connections are often hypoplastic or absent in many people, leading to an incomplete circle. The other percentage ranges are not consistent with anatomical studies: 5–10% is too low, while 50–60% and 75–85% are too high to reflect real variation.

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