Ultrasonography, CT for Post-EVAR Surveillance Debated

Hank Russell

NEW YORK -- Two imaging modalities for the examination and surveillance of patients after endovascular aneurysm repair were debated at the Veith symposium on vascular medicine sponsored by Montefiore Medical Center.

Making the case for duplex ultrasonography was Dr. Geoffrey L. Gilling-Smith of Royal Liverpool (England) University Hospital. He argued that duplex and plain films could do the job just as well as computed tomography (CT).

Taking the counterpoint was Dr. Ali AbuRhama of the Charleston (W.Va.) Area Medical Center, who argued that CT is not only better than ultrasonography, but more essential.

"It's very important that we need to survey these patients," Dr. Gilling-Smith said. "We can't ignore them. But we're looking for something that is both cheap and effective."

In a study he conducted, 99 patients in whom both CT and ultrasonographic scans had been performed throughout the follow-up were surveyed for at least 1 year. For each patient, CT and ultrasonographic measurements of maximal aneurysm diameter (MAD) were plotted and independently examined by two observers.

At each follow-up interval, MAD was compared with first postoperative and most recent MAD to determine if the aneurysm remained stable or had any changes in size. A change of more than 5 mm was considered significant. CT and ultrasonographic findings were compared to determine level of agreement.

In three patients, CT revealed expansion when ultrasonography (US) did not, according to Dr. Gilling-Smith. In each case, US revealed expansion at the next follow-up interval. No cause for expansion was identified or intervention required prior to ultrasonographic diagnosis.

In 18 patients, US revealed expansion when CT did not; 6 of them revealed expansion after a follow-up CT. In the remaining patients, CT and US were concordant.

Dr. Gilling-Smith also concluded that the abolition of CT scanning has resulted in a significant saving so that the cost of endovascular repair plus surveillance up to 4 years is close to the cost of open surgical repair.

Besides the costs (according to Dr. Gilling-Smith, one CT scan can cost up to $450), he argued that CT scans are also time consuming and can cause more harm to the patient.

"The radiation dose is huge," he said. "It's the equivalent of between 300 and 400 chest x-rays; that's 4 years of background radiation. There are also hematologic malignancies involved, to which the elderly population is more susceptible."

Dr. AbuRhama agreed that ultrasonography has some advantages. "The pros of having color duplex ultrasound [are, first] it is definitely noninvasive," he said. "Second, there is no use of intravenous contrast, which means no worries about allergies; and third, there is no radiation. Of course, color duplex ultrasound is approximately one-third the cost of a CT scan."

But when it came to image quality in detecting endoleaks, CT was the modality of choice, Dr. AbuRhama said.

"The studies that we had were quite suboptimal on the color duplex ultrasound, which means it was not conclusive in determining the two objectives in the study," he said. "The major objective was the ability to detect endoleaks after doing endovascular aneurysm repair."

In his study, although color duplex ultrasonography was able to detect type I endoleaks more accurately than CT (87.5% vs. 50%) and was able to hold its own in measuring the size of abdominal aortic aneurysms, CT showed greater sensitivity, especially in detecting type II endoleaks.

"It came out with the conclusion CT scanning could become the common modality if you are trying to confirm the presence of endoleaks," Dr. AbuRhama said. "That does not mean color duplex ultrasound is worthless; it's just that we cannot rely upon it totally [for] finding endoleaks in these patients."