Re. “Contrast Enhanced Ultrasound Can Replace Computed Tomography Angiography for Surveillance After Endovascular Aortic Aneurysm Repair”

Abstract

Re. "Contrast Enhanced Ultrasound Can Replace Computed Tomography Angiography for Surveillance After Endovascular Aortic Aneurysm Repair" We read with interest the paper by Bredahl et al. comparing the use of contrast enhanced ultrasound (CEUS) with duplex ultrasound (DUS) in the detection of post-EVAR leak, with the outcomes from those two groups benchmarked against computed tomography angiography (CTA). 1 The authors concluded that CEUS can potentially replace CTA for postoperative EVAR surveillance programmes based on similar detection rates of leaks that required re-intervention. Although a well-written paper, there are certain weaknesses with the methodology, implying that the conclusion should be taken with caution. The study lacked any mention of the cost in time, expenses, and personnel required to complete each scanning modality, although that was not the objective of the study. Based on our own observation, CEUS can have a learning curve and be time-consuming. Another limitation to external validity of this study is the need for referring all patients to a central unit staffed by individuals well-trained in performing the CEUS scans, unlike CTAs which can be performed in satellite hospitals and the images linked to be reported by the vascular radiology consultants based in the main tertiary unit. Also, we feel that one operator performing both ultrasound modalities in the same session, in the same sequence every time, would undoubtedly bias the results in favour of CEUS. In addition, with one individual performing all ultrasound scans the risk of an intra-observer error is not stratified, although we accept this has probably limited the risk of inter-observer error. On page 4, "In 278 patients, McNemar's chi-square test rejected the hypothesis that CEUS and CTA were diagnostically equivalent (p ¼ .002.), as opposed to CEUS compared with CTA (p ¼ .827)." The authors need to clarify which two tests are compared as they have CEUS and CTA in both. Lastly, the study lacked any form of power calculations, and therefore it is not fully clear if the sample size was adequate for analysis, or indeed to draw any conclusions. We feel that this study certainly generated some interesting hypotheses with regards to post-EVAR surveillance protocols; however, more evidence should be sought before recommending any change in practice.