A 58-year-old man from rural Maharashtra presents to the emergency department with sudden onset of severe abdominal pain radiating to the back, associated with hypotension (BP 88/54 mmHg) and tachycardia (HR 118/min). He has a history of hypertension and smoking. On examination, a pulsatile abdominal mass is palpated. CT angiography with contrast shows a 6.5 cm infrarenal aortic aneurysm with acute dissection and retroperitoneal hematoma. Which of the following anatomical relationships explains why rupture at this level presents with retroperitoneal bleeding rather than intraperitoneal bleeding?

Explanation

## Anatomical Basis of Retroperitoneal Rupture in Infrarenal AAA ### Retroperitoneal Location of Infrarenal Aorta **Key Point:** The infrarenal abdominal aorta lies **posterior to the peritoneum** within the retroperitoneal space, bounded anteriorly by the peritoneum and posteriorly by the vertebral bodies and psoas muscles. ### Clinical Significance When an infrarenal aortic aneurysm ruptures: - Blood accumulates in the **retroperitoneal space** (between peritoneum and posterior abdominal wall) - This is in contrast to suprarenal aortic ruptures, which may rupture into the peritoneal cavity - The retroperitoneal location initially contains bleeding, allowing time for hemostasis and emergency intervention ### Anatomical Layers (Superior to Inferior) | Structure | Layer | | --- | --- | | Visceral organs | Intraperitoneal | | Peritoneum | Peritoneal boundary | | **Infrarenal aorta** | **Retroperitoneal** | | Psoas major, vertebral bodies | Posterior abdominal wall | **High-Yield:** Retroperitoneal bleeding from AAA rupture may present with flank ecchymosis (Grey Turner's sign) and is often more survivable than intraperitoneal rupture because the retroperitoneal space provides temporary tamponade. **Clinical Pearl:** The classic triad of ruptured AAA is hypotension, pulsatile abdominal mass, and flank pain—all present in this patient. [cite:Standring Anatomy 41e Ch 62]