At the European Society for Vascular Surgery Annual Meeting (18–21 September 2013, Budapest, Hungary), Abeera Abbas, Academic Surgery Unit, Institute of Cardiovascular Sciences, University of Manchester, UK, presented the results from a pilot study which suggested that 3D contrast-enhanced ultrasound may be more sensitive to detect endoleaks when compared to both CT angiography and 2D contrast-enhanced ultrasound.
“EVAR surveillance is traditionally performed using CT angiography; however, CT angiography for is expensive and involves radiation exposure and nephrotoxic X-ray contrast agents. The other safe and inexpensive alternative is duplex imaging, but we cannot detect stent graft migration and fracture with this technique,” Abbas said. “In addition, some factors such as obesity and bowel gas can cause ultrasound technical. Moreover, we cannot perform 3D reconstruction using ultrasound imaging.”
She told delegates that, more recently, contrast-enhanced ultrasound imaging has been introduced, and that this technique has been reported to be more sensitive than CT angiography to detect endoleaks. Abbas said: “Three-dimensional (3D) contrast-enhanced ultrasound is a novel imaging technique that may be more sensitive to blood flow detection than CT angiography or 2D contrast-enhanced ultrasound. It utilises positional information from magnetic field emitters to assemble all ultrasound reflections into a high definition image.”
In the study, the investigators compared 3D contrast-enhanced ultrasound with CT angiography and 2D contrast-enhanced ultrasound for the detection of endoleak and aneurysm expansion following EVAR. They also aimed to assess the clinical utility of the new modality and to analyse the interobserver reliability to detect an endoleak.
The study recruited 23 EVAR surveillance patients in the University Hospital of South Manchester. All these patients had paired CT angiography performed as part of their routine surveillance programme. They had 3D contrast-enhanced ultrasound (Curefab) due to a clinical indication. The CT angiography was performed on a 16-slice helical scanner with a 1mm slice (Siemens), and 2D contrast-enhanced ultrasound was conducted with a Philips IU22.
Thirty paired 3D contrast-enhanced ultrasound and CT angiography images were analysed from the 23 patients. Endoleaks were detected in 17 images with CT angiography, 18 on 2D contrast-enhanced ultrasound and 18 on 3D contrast-enhanced ultrasound. The sensitivity, specificity, positive and negative predictive values of 3D contrast-enhanced ultrasound to detect endoleak were 100%, 92%, 94% and 100%, respectively. There was excellent correlation (r=0.935; p≤0.0001) between CT and 3D contrast-enhanced ultrasound for aneurysm sac diameter. Only 3D contrast-enhanced ultrasound builds an image of the route the endoleak takes and reliably shows the exit and entrance point in sac, detecting the inflow artery in all 18 scans with endoleak. Two-dimensional contrast-enhanced ultrasound detected the inflow in 16 (88.8%) and CT angiography on 12 (66.6%) images.
“The interobserver reliability analysis showed an almost perfect agreement between the two observers,” Abbas noted. “There was one ‘false positive’ result on 3D and 2D contrast-enhanced ultrasound, which is possibly a ‘true positive’ as this patient had an expanding aneurysm with oscillating thrombus in the sac, implying an intermittent endoleak which was thrombosed at the time of imaging. This endoleak was not seen on subsequent angiography but the clinical decision was to treat.”
Abbas stated that, in this study, only 3D contrast-enhanced ultrasound detected endoleaks in all cases, and concluded that this modality may be more sensitive to detect the source of an endoleak following EVAR than either 2D contrast-enhanced ultrasound or CT angiography. “It could also be safer and more cost-effective but before we adopt 3D contrast-enhanced ultrasound we need to perform a randomised controlled trial,” she said.