A Comparative Study of Ultrasound and Computed Tomography Scan for the follow-up of Abdominal Aortic Aneurysms after Endovascular Repair

Abstract

Objective

To date, computed tomography (CT) scanning has been the gold standard for follow-up of abdominal aortic aneurysms (AAA) after endovascular repair (EVR). However, with increasing durability of the minimally invasive procedure and longer survival of patients, there is concern over the expense of CT and its associated risks. For this reason, many now believe that ultrasound (US) may be an adequate substitute for surveillance of patients after EVR. The aim of this study was to compare ultrasound and CT scan in our practice to ascertain whether ultrasound alone would be sufficient for follow-up of AAA patients after EVR.

Materials and Methods

A total of 121 patients underwent EVR of AAAs during a 6-year period. All patients were followed up annually using both CT scanning and US. The parameters assessed included the presence/absence of endoleaks, as well as diameters of the aneurysm sac and neck. Results were plotted graphically to determine the change in size of aneurysms over time, and patients with endoleaks were compared with those who had no endoleaks. The sensitivity, specificity, positive, and negative predictive values for detecting endoleaks was also calculated for US and CT. Normally distributed data were analyzed using the Student's t-test and the Wilcox-signed rank test was used for nonparametric data.

Results

A total of 573 (CT and US) scans were analyzed. Of these, 391 scans (91 patients) did not show endoleaks. There were 64 scans (18 patients) in which both CT and US detected endoleaks; 6 scans (6 patients) in which CT detected leaks and US did not; and 5 scans (4 patients) in which US detected leaks and CT did not. The aneurysm sac size increased over time in the endoleak group and decreased over time in the nonendoleak group, whereas neck sizes did not change in either patient group. The sensitivity, specificity, positive, and negative predictive values of US and CT scan for detecting endoleak were 92.7%, 98.5%, 91.4%, and 98.7%; and 91.4%, 98.7%, 92.7%, and 98.5% respectively.

Conclusion

In our practice, US was comparable with CT scan for the detection of endoleaks, and similar trends were seen over time with regard to changes in aneurysm neck and body sizes for both modalities. We believe that US should be the primary modality for follow-up of patients after EVR and that CT scan should be reserved for confirmation of endoleak where this is suspected.