What are the duplex ultrasound signs that characterize an "Unstable abdominal aortic aneurysm sac" after endograft implantation?

Introduction. - Classification of endoleak is determined by the mechanism by which the endograft fails to exclude the aneurysm. In some instances, the endoleak may be very subtle or not visible; yet, the aneurysm continues to expand. This report presents our experience in identifying unstable abdominal aortic aneurysm sacs associated with endoleaks or endotension in early and late monitoring using color duplex ultrasound (CDU) in a series of more than 1000 endograft patients. Aims. - We sought to (1) describe ultrasound features of atypical endoleaks and endoleaks from unusual sources and (2) characterize other CDU features that may be associated with endotension. Methods. - Philips HDI 5000 and IU22 machines were used during routine post-endograft surveillance scans of the abdominal aorta. Color, spectral, and power Doppler analysis were also performed to identify evidence of perigraft flow, graft stenosis, thrombus, kink, or migration. Secondary diagnostic maneuvers were conducted in the presence of perigraft flow to characterize the type of endoleak. Particular attention was also paid to the abdominal aortic aneurysm sac contents, size, and pulsatility. Correlation was made to angiography and computed tomography imaging in a series of 22 patients who underwent secondary endograft procedures or open conversion. Results. - Technically satisfactory studies were achieved in approximately 90% of patients. We detected type II endoleaks in 10% of patients assessed and graft migration in 12 cases. Endotension was characterized by sac enlargement and/or shape change without identifiable perigraft flow and correlated highly with device migration. Suggestive features of graft/sac instability included increased sac pulsatility, prominent areas of echolucency within the sac, and occasional low-amplitude atypical color signals within the sac thrombus close to the graft wall. Conclusion. - Reliable CDU assessment for late endograft follow-up requires careful scrutiny of the aneurysm sac contents and wall, as well as the graft device. Endoleak may not always be obvious yet CDU features can assist in identifying the source of endoleak or the presence of endotension. There are suspicious ultrasound features that may alert one to graft/sac instability and potentially dangerous outcome.