A 68-year-old man with a history of hypertension and smoking presents to the emergency department with sudden-onset severe back pain and hypotension. Imaging confirms a ruptured abdominal aortic aneurysm. What is the most common site of rupture in an abdominal aortic aneurysm?

Explanation

## Anatomical Site of AAA Rupture **Key Point:** The **left posterolateral wall below the renal arteries** is the most common site of rupture in abdominal aortic aneurysms (AAAs). This is a well-established anatomical fact in vascular surgery. ### Pathophysiological Basis 1. **Infrarenal predilection**: The vast majority (~95%) of AAAs are infrarenal. Below the renal arteries, the aortic wall loses the support of the paired renal artery ostia and has a relative deficiency of vasa vasorum, leading to medial degeneration and aneurysm formation (Rutherford's Vascular Surgery). 2. **Left posterolateral predominance**: Asymmetric expansion of the aneurysm sac preferentially stresses the **left posterolateral wall** due to the anatomical curvature of the infrarenal aorta and the eccentric distribution of intraluminal thrombus, which paradoxically does NOT protect the wall from rupture. 3. **Retroperitoneal containment**: Rupture through the left posterolateral wall dissects into the **left retroperitoneal space**, which can temporarily tamponade the hemorrhage — explaining why some patients survive long enough to reach the hospital ("contained rupture"). ### Why NOT the Other Options? - **Option A (Right lateral wall above renal arteries)**: Suprarenal AAA rupture is genuinely rare; the suprarenal aorta is reinforced by the renal artery origins and has better medial support. - **Option C (Anterior wall at SMA level)**: Anterior rupture leads to free intraperitoneal hemorrhage and rapid exsanguination; it is less common (~15–20%) and occurs at a different level. - **Option D (Posterolateral at the level of renal arteries)**: While posterolateral is correct, the rupture characteristically occurs **below** (infrarenal), not at the level of, the renal arteries. ### Clinical Significance **High-Yield:** The classic triad of contained retroperitoneal rupture: - Sudden severe **back or flank pain** - **Hypotension** (often relative initially due to retroperitoneal tamponade) - **Pulsatile abdominal mass** (palpable in ~50%) **Clinical Pearl:** Grey Turner sign (flank ecchymosis) is a late finding of retroperitoneal hematoma tracking along fascial planes. Anterior rupture into the peritoneal cavity causes rapid cardiovascular collapse with near-100% pre-hospital mortality. ### Comparison of Rupture Sites | Site | Frequency | Space | Outcome | |------|-----------|-------|---------| | **Left posterolateral (infrarenal)** | **~70–80%** | Retroperitoneal | Contained → relative stability | | Anterior wall | ~15–20% | Intraperitoneal | Free hemorrhage, rapid shock | | Right posterolateral | Less common | Retroperitoneal | Similar to left | | Suprarenal / at renal level | Rare | Variable | Depends on extent | [cite: Rutherford's Vascular Surgery 9e; Schwartz's Principles of Surgery 11e Ch 23]