Rank the arteries most to least likely to have a saccular (berry) aneurysm in the circle of Willis.

Rank the arteries most to least likely to have a saccular (berry) aneurysm in the circle of Willis.

• A. PCA, MCA, ICA, ACA
• B. ACA, MCA, ICA, PCA
• C. ACA, ICA, MCA, PCA
• D. MCA, ACA, PCA, ICA

Answer: (B)

Berry aneurysms most often form at arterial branching points where the vessel wall is weakest and hemodynamic stress is highest. In the circle of Willis, the anterior circulation carries the highest incidence, with the aneurysm most commonly at the junction where the anterior communicating artery meets the anterior cerebral arteries. That makes the anterior cerebral artery territory the most likely site. The next most common site is at the middle cerebral artery bifurcation, where a branch point also experiences significant flow and wall stress. Aneurysms along the internal carotid artery are less common than those in the ACA or MCA regions, and aneurysms involving the posterior circulation, including the posterior cerebral arteries, are the least common. Therefore the rank from most to least likely among the listed arteries is ACA, then MCA, then ICA, and finally PCA.

Berry aneurysms most often form at arterial branching points where the vessel wall is weakest and hemodynamic stress is highest. In the circle of Willis, the anterior circulation carries the highest incidence, with the aneurysm most commonly at the junction where the anterior communicating artery meets the anterior cerebral arteries. That makes the anterior cerebral artery territory the most likely site. The next most common site is at the middle cerebral artery bifurcation, where a branch point also experiences significant flow and wall stress. Aneurysms along the internal carotid artery are less common than those in the ACA or MCA regions, and aneurysms involving the posterior circulation, including the posterior cerebral arteries, are the least common. Therefore the rank from most to least likely among the listed arteries is ACA, then MCA, then ICA, and finally PCA.