Endoleak, or persistent blood flow in the aneurysm sac outside of the endograft, is the most frequent complication after EVAR and has been reported in nearly one in four patients at some time during follow-up. There are four types of endoleaks:

• Type I endoleak occurs in the absence or loss of complete sealing at the proximal (Type IA) or distal (Type IB) end of the stent graft.
• Type II endoleaks are the most common form of endoleak and arise from retrograde filling of the sac by lumbar branches or the inferior mesenteric artery.
• Type III endoleaks arise from poorly seated modular connections or from disconnection and separation of components. Less often it is the result of fabric erosion related to material fatigue.
• Type IV endoleaks represents self-limiting blood seep- age through the graft material due to porosity and treatment is not required. Typically, this form of endoleak is only noted at the time of repair on post-implantation intra-operative angiography.