Which endoleak type is characterized by retrograde flow from collateral vessels?

• A. Type I – leak at the proximal/distal seal
• B. Type III – graft fabric/connection failure
• C. Type IV – graft porosity
• D. Type II – retrograde flow from collateral vessels

Answer: (D)

Endoleaks after EVAR are categorized by how the aneurysm sac reaccumulates blood. The one driven by retrograde flow from collateral vessels fills the sac from branches like lumbar arteries or the inferior mesenteric artery. This backflow is typically low pressure and can be self-limiting, which is why many of these leaks are managed with observation and surveillance. On imaging, you’ll see the aneurysm sac lighting up due to backfilling from feeders rather than a direct seal breach. Intervention is reserved for sac enlargement or persistence, where targeted embolization of the feeding arteries or direct sac embolization can seal off the backflow. In contrast, other endoleaks arise from high-pressure leaks at the graft seals, or from graft material or porosity, which require distinctly different management.