During a cadaveric dissection, a medical student identifies the most common site of abdominal aortic aneurysm (AAA) formation. Which segment of the abdominal aorta is the most frequent location?

Explanation

## Abdominal Aortic Aneurysm: Anatomical Distribution **Key Point:** The infrarenal abdominal aorta is the most common site of AAA formation, accounting for 90% of all abdominal aortic aneurysms. ### Anatomical Classification of AAA by Location | Segment | Frequency | Key Features | Clinical Relevance | |---------|-----------|--------------|-------------------| | **Infrarenal** | ~90% | Below renal arteries; most common | Standard surgical/endovascular repair | | Suprarenal | ~5% | Above renal arteries; involves renal ostia | Complex repair; higher morbidity | | Juxtarenal | ~3% | At renal artery level; involves renal arteries | Requires renal artery reconstruction | | Iliac | ~2% | Isolated iliac aneurysm | Often extends from AAA | **High-Yield:** Infrarenal AAA is the classic presentation. When a patient presents with AAA, assume infrarenal unless otherwise specified. ### Why Infrarenal Segment is Most Common 1. **Hemodynamic factors:** The infrarenal aorta experiences greater turbulent flow and shear stress due to the aortic bifurcation 2. **Structural weakness:** The infrarenal aorta has fewer elastic fibers and less muscular support compared to the suprarenal segment 3. **Atherosclerotic burden:** Atherosclerosis is more prevalent in the infrarenal aorta, a major risk factor for AAA formation 4. **Genetic predisposition:** Familial AAA (10% of cases) also predominantly affects the infrarenal segment **Clinical Pearl:** Infrarenal AAA can be repaired with standard techniques (tube graft or bifurcated graft) without renal artery involvement. Suprarenal AAA requires more complex reconstruction and carries higher perioperative morbidity and mortality. ### Risk Factors for AAA - Atherosclerosis (most common) - Smoking (strongest modifiable risk factor) - Male gender (5–10:1 male predominance) - Age >65 years - Hypertension - Family history - Connective tissue disorders (Marfan, Ehlers-Danlos) **Mnemonic:** **AORTA** — Atherosclerosis, Age, Older males, Rupture risk, Tobacco — key risk factors and features of AAA.