Which is the most common site of aneurysm formation within the Circle of Willis?

Explanation

## Aneurysm Sites in the Circle of Willis **Key Point:** The anterior communicating artery (AComm) is the most common site of saccular aneurysm formation, accounting for approximately 30–35% of all intracranial aneurysms. ### Anatomical Basis The anterior communicating artery is a small, short vessel connecting the two anterior cerebral arteries. It experiences high hemodynamic stress due to: - Asymmetry in flow from the two ACAs - Abrupt change in vessel caliber - Turbulent flow patterns at the junction ### Frequency Distribution of Aneurysms | Location | Frequency | Clinical Significance | | --- | --- | --- | | **Anterior communicating artery** | **30–35%** | **Most common; high risk of rebleeding** | | Posterior communicating artery | 30–35% | Second most common; often asymptomatic | | Middle cerebral artery bifurcation | 20–25% | Third most common | | Basilar artery tip | 5–10% | Rare; high mortality if ruptured | | Vertebral artery junction | 3–5% | Rare | **High-Yield:** The **"top 3 sites"** (AComm, PComm, MCA bifurcation) account for >85% of all saccular aneurysms. These are tested frequently in NEET PG. ### Clinical Pearl Aneurysms at the AComm are particularly prone to: - Intraventricular hemorrhage (due to proximity to the lamina terminalis) - Rebleeding within the first 2 weeks - Vasospasm and delayed cerebral ischemia **Warning:** Do not confuse the most common site with the most common *symptom*. AComm aneurysms present with SAH, headache, and neck stiffness — but the location itself (not the symptom) is what is being asked. [cite:Robbins 10e Ch 28]