CT Colonography Matches Colonoscopy for Detecting Advanced Polyps

MADISON, Wis., Oct. 3 -- CT colonography, the heir presumptive to optical colonoscopy, has won a clinical round here for detection of developing neoplasia.

The noninvasive modality, better known as virtual colonoscopy, equaled standard colonoscopy in a study of more than 6,000 patients, producing similar detection rates for advanced neoplasia, David H. Kim, M.D., of the University of Wisconsin, and colleagues reported in the Oct. 4 issue of the New England Journal of Medicine.

It was the latest chapter in the growing competition between the two modalities for initial colorectal cancer screening, a rivalry that may erupt into a major turf battle between gastroenterologists and radiologists.

In an interview Dr. Kim, a radiologist, said that despite suggestions of a turf war between radiologists and gastroenterologists, "I personally don't think this should happen."

He cited the potential pool of patients-some 40 million-- who need screening that is so large, a turf war this would be unlikely. "The choice of the two methods would bring in patients for screening who would otherwise remain on the sidelines," he said. "We need both methods at full capacity to get all who require screening. Use either method. Just pick one and do it."

To compare the diagnostic yield from parallel studies of CT colonography and optical colonoscopy, the researchers compared primary CT screening in 3,120 consecutive patients (mean age 57) with 3,163 consecutive primary colonoscopy patients (mean age, 58.1).

Colonoscopy followed CT colonography for removal of polyps of at least 6 mm. Referral for polypectomy during same-day therapeutic colonoscopy was offered to all patients with CT-detected polyps of at least 6 mm.

Patients with one or two small polyps (6 mm to 9 mm) were given the option of continued CT surveillance. However, during primary colonoscopy, nearly all detected polyps were removed, regardless of size, according to established practice guidelines

The researchers wrote that most very small polyps are not adenomatous and only a small fraction of all adenomas are advanced, suggesting a need for a more selective alternative to the practice of universal polypectomy.

Advanced neoplasia of the colon consisted of both adenocarcinomas and a subgroup of benign neoplasms referred to as advanced adenomas, but associated with a relatively high risk of progression to cancer, the researchers wrote.

An advanced adenoma iwas defined as an adenoma that meets one or more of the following criteria: at least 10 mm in size, a substantial villous component, and high-grade dysplasia.

During CT screening, 123 (14 invasive) advanced neoplasms were found, while for colonoscopy 121 (four invasive) advanced neoplasms were found. The referral rate for colonoscopy in the primary CT screening group was 7.9% (246 of 3,120 patients).

Advanced neoplasia was confirmed in 100 of the 3,120 patients in the CT group (3.2%) and in 107 of the 3,163 patients in the primary colonoscopy group (3.4%).

This did not include 158 patients with 193 unresected CT-detected polyps, 6 mm to 9 mm, who were undergoing surveillance.

However, the number of polypectomies performed to achieve these similar outcomes differed significantly between the two groups, with more than four times as many polyps removed in the colonoscopy patients group as in the CT patients (2,434 versus 561).

The rates of positive results for the two screening strategies were similar at the 10-mm and 6-mm thresholds, but the large disparity in polypectomies reflected the different management of diminutive lesions, the researchers said.

According to limited follow-up data for the 158 patients with one or two polyps (6 mm to 9 mm) undergoing surveillance, 54 returned for CT follow-up with findings of 70 small polyps.

Of this group, 67 polyps (96%) have remained stable or decreased in size at follow-up. Three polyps grew at least 1 mm but did not cross the 10-mm threshold, and were all removed. Histologic examination revealed tubular adenomas without high-grade dysplasia.

Serious adverse events during primary colonoscopy screening included colonic perforation in seven patients (0.2%) with surgical repair required for four.

There were no perforations or other serious complications from subsequent therapeutic colonoscopy after a positive CT examination, the researchers said.

A major limitation of the study was the lack of randomization posing a potential for selection bias, possibly leading to different prevalences of advanced adenomas.

The marked decrease in the use of colonoscopy and the lower rates of polypectomies in the CT patients suggests that this technique is a safe, clinically effective, and cost-effective filter for therapeutic colonoscopy, the researchers said.

Furthermore, by combining both methods, with the test choice driven by patient preference, the overall screening compliance for total colonic examination could substantially increase, they concluded.