Follow-up of aortic stent grafts: comparison of the volumetric analysis of the aneurysm sac by ultrasound and CT.

BACKGROUND

The long-term follow-up of patients with endovascular aneurysm repair (EVAR) and a normal surgical risk was defined by the French National Authority for Health (Haute Autorité de Santé) in 2009. The monitoring of the volume of the aneurysm sac theoretically avoids the bias related to the measurement of its diameter alone. The objective of this study was to evaluate how reliable and reproducible the volumetric measurement of the aneurysm sac by ultrasound was compared with computerized tomography angiography (CTA).

METHODS

We carried out a retrospective diagnosis study of 75 consecutive patients treated with EVAR in our institution who were monitored with 3-dimensional ultrasonography (3DU) and CTA between January 2010 and December 2012. The measurement of the volume (cm(3)) of the aneurysm sac with a Toshiba Aplio XG ultrasound system equipped with a 3-MHz 3-dimensional probe was compared with the volume obtained by CTA. Interoperator reproducibility was studied in the last 45 enrolled patients; 2 different blinded operators made 2 volumetric measurements on the same patients, on the same day. An analysis of a 48-patient subgroup in which at least two 3DU were performed during follow-up was also carried out to determine the threshold value of the increase in the volume of the aneurysm sac, making it possible to suspect the presence of an endoleak.

RESULTS

A total of 116 pairs of examinations were compared (the patients who had the longest postoperative follow-up had 4 pairs of compared examinations). The correlation between volumetric ultrasound and CTA measurements was excellent (r = 0.931; P < 0.0001) in the 116 pairs of examinations, and so was the reproducibility of volumetric echography (r = 0.949; P < 0.0001) in 45 patients. The subgroup study highlighted the fact that a 6.5-cm(3) increase of the aneurysm sac made it possible to suspect the presence of an endoleak in comparison with CTA as the gold standard (sensitivity and specificity were 85.7% and 85.3%, respectively). The area under the curve was 0.854 (95% confidence interval, 0.793-0.915). In the 116 examinations, a good correlation between volume and diameter was calculated with CTA (r = 0.733; P < 0.0001) and between ultrasound volumetric and CTA diameter (r = 0.660; P < 0.0001).

CONCLUSIONS

Volumetric echography is comparable with CTA for the evaluation of the aneurysm sac after EVAR, reproducible and inexpensive. When a significant increase of the volume of the sac is detected by ultrasound, the examination can be supplemented by an injection of ultrasound contrast agent or by CTA to visualize an endoleak.