a Most endoleaks fed by an inferior mesenteric artery are high-ow endoleaks. In the case shown, peak systolic velocity (PSV) is 138cm. Such high-ow endoleaks rarely close spontaneously, even if only a small portion of the excluded aneurysm sac shows ow signals. b The CT angiogram conrms that ow is conned to a small portion of the aneurysm sac; however, ow into the sac is already seen during the arterial phase. Follow-up 3months later conrmed a persistent high-ow endoleak (based on duplex ultrasound criteria) and an 8-mm increase in the diameter of the residual aneurysm sac (not shown). Endoleak embolization was performed. c Follow-up 6months later shows a new low-ow endoleak with a PSV of 27cm/s (fed by a lumbar artery, ow coded in blue). The endoleak is located more peripherally, posterior to one of the iliac limbs. There is a mirror artifact with red-coded ow (same ow direction as within the stent graft). The waveform demonstrates to-and-fro ow with systolic inow (S) and diastolic outow (D), conrming the endoleak (as this is a ow pat­tern that does not occur physiologically). This small endoleak requires monitoring but no treatment. d In the CT angiogram, the small endoleak cannot be identied with certainty. In addition, there is a small posterior plaque, which may be mistaken for an endoleak (in conjunction with the ndings of contrast-enhanced ultrasound (CEUS)). Note that, in contrast-enhanced CTA, an endoleak fed by a patent lumbar artery may be opacied rather late, i.e., during the venous phase or even later (due to longer transit time of the contrast microbubbles through lumbar arteries). As a result, such endoleaks may even be missed by CTA. e The type II endoleak identied by color duplex imaging in this patient and fed by a lumbar artery is more conspicuous in the CEUS examination (arrow) compared with CTA.