A 58-year-old man from rural India presents to the emergency department with a 6-hour history of sudden-onset severe epigastric pain radiating to the back, associated with nausea and diaphoresis. Blood pressure is 92/58 mmHg, heart rate 118/min. Physical examination reveals a pulsatile abdominal mass. CT angiography shows a 6 cm infrarenal abdominal aortic aneurysm with rupture into the retroperitoneum. The surgeon notes that the aneurysm extends from just below the renal arteries to the aortic bifurcation. Which of the following branches of the abdominal aorta would be at highest risk of compromise during emergency repair of this aneurysm?

Explanation

## Anatomical Course of Infrarenal Aortic Aneurysm **Key Point:** An infrarenal abdominal aortic aneurysm (AAA) lies between the renal arteries (which arise at L1–L2) and the aortic bifurcation (at L4–L5). The infrarenal segment gives off the testicular/ovarian arteries and the lumbar arteries, but the major visceral branches have already originated proximal to this level. ## Vascular Anatomy of the Abdominal Aorta | Branch | Origin Level | Relationship to Infrarenal AAA | |--------|--------------|--------------------------------| | Celiac trunk | T12–L1 | **Proximal** — above the aneurysm | | Superior mesenteric artery (SMA) | L1 | **Proximal** — above the aneurysm | | Renal arteries | L1–L2 | **Proximal** — above the aneurysm | | Inferior mesenteric artery (IMA) | L3 | **Within or at margin** of infrarenal AAA | | Aortic bifurcation | L4–L5 | **Distal** — below the aneurysm | **High-Yield:** The IMA typically arises at the level of L3, which falls squarely within the infrarenal aortic segment. During emergency repair (cross-clamping and graft placement), the IMA origin is often ligated or compromised, especially if the aneurysm is large or extends to the bifurcation. ## Clinical Consequence of IMA Compromise **Clinical Pearl:** Ligation of the IMA during AAA repair can lead to ischemic colitis, particularly if the inferior hemorrhoidal arteries and marginal artery of Drummond are not patent. The left colon and sigmoid colon rely on IMA blood supply; if collaterals are inadequate, transmural necrosis may occur. This is a recognized complication in 2–10% of AAA repairs and carries significant morbidity. **Warning:** Do not confuse the level of origin with the risk of compromise. The celiac and SMA arise well above the infrarenal segment and are typically not directly involved in the aneurysm itself, though they may be affected if the aneurysm extends proximally (juxtarenal or suprarenal AAA). ## Why the Other Branches Are Not at Highest Risk - **Celiac trunk & SMA:** Arise proximal to the renal arteries (at T12–L1 and L1, respectively); the aneurysm is infrarenal, so these are anatomically distant and not directly at risk during standard repair. - **Renal arteries:** Arise at the proximal margin of the infrarenal segment; they are typically preserved during repair because they supply the kidneys and are critical for renal function. [cite:Standring Anatomy 41e Ch 61]