Endoleak Type II is most commonly due to retrograde flow from which vessels into the aneurysm sac?

• A. Visceral arteries
• B. Branch vessels such as lumbar or inferior mesenteric arteries
• C. External iliac arteries
• D. Renal arteries

Answer: (B)

Type II endoleaks occur when blood flows backward into the aneurysm sac from collateral branches after EVAR. The most common sources are branch vessels that originate from the aorta near the aneurysm, especially the lumbar arteries and the inferior mesenteric artery. These vessels can remain patent and feed the sac in a retrograde fashion despite the graft sealing the main inflow, leading to persistent sac pressurization. The other vessels listed are not typical sources of a Type II endoleak: visceral and renal arteries are primary branches that, if involved, relate to different leakage patterns or graft issues, and the external iliac arteries are not usually retrograde feeders into the sac. So the classic culprits are the lumbar arteries and the inferior mesenteric artery feeding the sac.