Report from ARRS: Virtual colonoscopy gets an A for safety

May 4, 2006

As if CT colonography needed more good publicity, a multinational study of more than 20,000 procedures has found that the technique is safer than previously thought, with a serious complication rate of just .018%.

As if CT colonography needed more good publicity, a multinational study of more than 20,000 procedures has found that the technique is safer than previously thought, with a serious complication rate of just .018%.

The Working Group on Virtual Colonoscopy survey represents screening and diagnostic CTC experience at 16 medical centers in five countries since 1997. Results were presented at the American Roentgen Ray Society meeting on Tuesday.

To gauge safety, researchers recorded the symptomatic perforation rate and overall rate of significant complications, defined as events landing a patient in the hospital. Of 21,923 studies, only four cases of significant complications occurred.

Improving the safety profile in part is the automated carbon dioxide delivery technique for colonic distention, which was used in roughly 40% of the 20,000-plus procedures. This method is safer as well as easier than manual room air insufflation, according to presenter Dr. Perry Pickhardt, an associate professor of radiology at the University of Wisconsin Medical School.

Other studies that had reported higher complication rates made greater use of manual room air insufflation. Patient selection could also explain differences in complication rates.

The Working Group study found no reports of symptomatic perforation in patients who underwent automated carbon dioxide delivery or CTC for screening. All of the complications took place during diagnostic studies, which accounted for about 46% of the procedures.

As CTC becomes more established, treatment and follow-up of detected lesions are drawing greater attention. In another study, researchers said it might be possible to identify advanced adenomas - benign lesions that are most likely to progress to cancer - with CTC and follow those that appear to be less threatening, reducing the number of polypectomies.

Advanced adenomas form a small subset of colonic adenomas. They are defined as adenomas 10 mm or greater in size or those that have a villous component or high-grade dysplasia.

Researchers at the University of Wisconsin performed a retrospective review of two CTC databases, which included 3536 screening procedures of asymptomatic patients. The mean age was 57, and there was a roughly an equal gender split among patients. They assessed detection of advanced adenomas, which is main aim of colorectal screening.

Of the 325 adenomas over 6 mm in size, 208 were medium sized (6 to 9 mm), and 117 were large (greater than or equal to 10 mm), said Dr, David Kim, an assistant professor of abdominal imaging at Wisconsin.

Of the total, 124 were advanced adenomas. The mean size of advanced adenomas was large: 94% of lesions were greater than 10 mm, while only 5.6% were 6 to 9 mm. All cases of polyps with invasive carcinoma were in the 10 mm or greater category. Furthermore, there was only one advanced adenoma with high-grade dysplasia in the 6 to 9 mm group (prevalence of 0.028%).

Prevalence of advanced adenomas in the overall screening population was just 3.1%

The results indicate that size may be a useful surrogate marker for advanced adenomas and that follow-up surveillance with CTC may be an option for some patients with 6 to 9-mm polyps, given the very low occurrence of invasive carcinoma or high-grade dysplasia in this group, Kim said. The small number of lesions likely to turn into cancer could be removed at polypectomy, while most lesions would be stable or regress, avoiding unnecessary procedures.

It's unclear whether this concept will catch on with gastroenterologists, who have had a mixed reaction to the results, according to Kim. Awareness of potentially unnecessary polypectomies is growing, however, and sentiments about CTC surveillance could change.

"A tremendous number of polyps are being removed. All of these polypectomies carry procedural risks. If we could find a way to cut down on polypectomies without sacrificing our screening goals, that would be favorable," Kim said.