Which artery located inferior to the IMA and superior to the aortic bifurcation is a source of collateral flow to the lower extremity?

• A. Median Sacral Artery
• B. Lumbar Artery
• C. Inferior Phrenic Artery
• D. Superior Mesenteric

Answer: (A)

The main idea is that collateral blood flow to the lower extremity can come from a midline aortic branch that sits between the inferior mesenteric artery and the aortic bifurcation. The median sacral artery fits this spot: it arises from the posterior aspect of the aorta just below the origin of the inferior mesenteric artery, then travels downward along the midline toward the sacrum and forms connections with the lateral sacral and pelvic/iliac arteries. Through these connections, it can contribute to collateral circulation to the lower limbs when primary routes are blocked.

Other arteries listed either originate higher or take a different path. The lumbar arteries are paired lateral branches of the aorta supplying the posterior abdominal wall rather than serving as a midline conduit to the legs. The inferior phrenic artery and the superior mesenteric artery are located well above the aortic bifurcation and are not the midline route described for pelvic-to-limb collateral flow.