Radiology: Contrast-enhanced US could cut EVAR follow-up risks

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Abdominal aortic aneurysm (AAA) stents with bilateral iliac arteries - 86.91 Kb
Digital CT showing endovascular stenting of an abdominal aortic aneurysm with bilateral iliac aneurysms, using a techniques that preserves flow into both internal iliac arteries (purple arrows) Source: The Cleveland Clinic

Contrast-enhanced ultrasound may complement CT angiography surveillance of patients following endovascular repair of abdominal aortic aneurysms (EVAR) and help curb the risk of kidney toxicity, according to a study published online May 15 in Radiology.

Although EVAR has improved perioperative mortality compared with open repair of abdominal aortic aneurysms, patients outcomes may be comprised by an endoleak. Endoleak, or arterial perfusion of the aneurysm sac, has been reported in 4 to 30 percent of EVAR patients and can predict post-EVAR aortic rupture. Thus, routine post-EVAR surveillance is essential. CT angiography serves as the standard, but radiation exposure and contrast agent nephrotoxicity represent ongoing concerns with the approach.

Neither MRI nor first-generation color Doppler ultrasound provides a widely effective alternative for surveillance. Second-generation ultrasound contrast agents offer expanded diagnostic capability and may enable surveillance of EVAR patients.

“The main advantage of contrast-enhanced ultrasound is that it offers the possibility of real-time exploration of EVAR-treated patients, without the exposure to ionizing radiation or the risk of damage to the kidneys,” study author Rosa Gilabert, MD, PhD, from the diagnostic imaging center at University of Barcelona in Spain, said in a statement. “To avoid the potential risk of kidney toxicity is particularly important, because impaired renal function is not uncommon in these patients.”

Thus, Gilabert and colleagues devised a prospective study to evaluate the accuracy of contrast-enhanced ultrasound in the detection and classification of endoleaks using CT angiography as a reference standard.

The researchers enrolled 35 EVAR patients (34 men, one woman) between January 2004, and December 2006. Participants underwent CT angiography and abdominal radiography at one, six and 12 months after EVAR, and then annually if there were no complications. Contrast-enhanced ultrasound was performed on the same day or within one month of CT angiography.

Two radiologists blinded to other imaging data conducted color Doppler and contrast-enhanced ultrasound and reviewed images for the presence or absence of an endoleak.

After a mean patient follow-up of 18.6 months, Gilabert et al analyzed 126 paired CT angiography and contrast-enhanced ultrasound datasets.

Among the 35 patients, 16 were diagnosed with an endoleak. CT angiography showed the endoleak in 34 studies. Contrast-enhanced ultrasound identified 33 of the 34 endoleaks and delivered sensitivity, specificity, positive and negative predictive values, and accuracy of 97 percent, 100, percent, 100 percent, 98 percent and 99 percent, respectively.   

“[Contrast-enhanced ultrasound] enables real-time study of blood flow, and its minimal invasiveness and good tolerability are in keeping with the necessity of avoiding the deleterious effect on renal function that CT angiographic contrast agent injection has in these patients,” wrote Gilabert et al.

The researchers explained that contrast-enhanced ultrasound could complement CT angiography in EVAR follow-up and suggested that the exam replace CT angiography one year after EVAR in patients with stable or decreasing aneurysm sac size and no evidence of an endoleak on CT angiography.