Which of the following is the most common site of rupture in an abdominal aortic aneurysm (AAA)?

Explanation

## Rupture Sites in Abdominal Aortic Aneurysm **Key Point:** The posterolateral wall rupture into the retroperitoneal space is the most common presentation of AAA rupture, accounting for approximately 70–80% of cases. ### Why Posterolateral Rupture is Most Common The posterolateral wall of the abdominal aorta is the weakest point because: - The aorta lacks posterior peritoneal coverage in the infrarenal region - The posterior wall is in direct contact with the vertebral bodies and retroperitoneal tissues - Aneurysmal degeneration preferentially affects the posterolateral aspect due to hemodynamic stress - The retroperitoneal space acts as a natural tamponade, allowing temporary containment and survival to hospital ### Clinical Significance **High-Yield:** Posterolateral rupture into the retroperitoneal space allows the patient to reach hospital alive in ~50% of cases because the retroperitoneum provides temporary hemostasis. In contrast, rupture into the peritoneal cavity (anterolateral) is rapidly fatal. ### Rupture Site Comparison | Site | Frequency | Outcome | Clinical Presentation | |------|-----------|---------|----------------------| | Posterolateral (retroperitoneal) | 70–80% | Often survives to hospital | Flank pain, hypotension, pulsatile mass | | Anterolateral (peritoneal) | 15–20% | Rapidly fatal | Sudden collapse, massive hemorrhage | | Aortoduodenal | 5–10% | Hemodynamic instability | GI bleeding, sepsis (if contained) | | Other sites | <5% | Variable | Rare | **Clinical Pearl:** The "contained rupture" (posterolateral into retroperitoneum) is a critical concept — it represents a window of opportunity for emergency surgical or endovascular intervention before exsanguination occurs. [cite:Robbins 10e Ch 10]