Compared with optical colonoscopy, CT colonography achieves similar outcomes with a fraction of the number of polypectomies, according to a study of more than 6,200 patients from the University of Wisconsin Medical School.

Perry Pickhardt, MD, associate professor of radiology at Wisconsin, and colleagues reported results in The New England Journal of Medicine in October (Kim et al: 357:1403-1412, 2007). Their experience supports CTC surveillance for polyps sized 6 to 9 mm, rather than polypectomy, according to the authors.

"The 10-mm threshold for polypectomy at asymptomatic screening would probably capture the vast majority of clinically relevant lesions," they said.

The NEJM publication followed on the heels of the release of results from the American College of Radiology Imaging Network (ACRIN) screening trial, which found similar sensitivity and specificity for the two screening techniques (see discussion below). And European trial results were presented only weeks after publication of the Wisconsin data (see below). Supporters hope these studies will help virtual colonoscopy take off in mainstream screening.

NEJM study

In the NEJM study, researchers compared the screening techniques in two different groups of about 3,100 consecutive asymptomatic, average-risk adults. They assessed detection rates of advanced adenomas, defined as polyps ≥ 10 mm or polyps below that size with high-grade dysplasia or a prominent villous component.

CTC detected 123 advanced adenomas (in 3.2% of patients), including 14 invasive cancers. Optical colonoscopy yielded 121 advanced adenomas (in 3.4% of patients), including 4 invasive cancers.

Polyps were placed into three categories: diminutive (≤ 5 mm), small (6 to 9 mm), or large (≥ 10 mm). In the CTC group, polyps 10 mm or larger were removed during subsequent therapeutic optical colonoscopy, but patients with polyps sized 6 to 9 mm were given the option of CTC surveillance. The optical colonoscopy screening protocol called for removal of all polyps, including diminutive findings. Consequently, the total number of polyps removed was much larger in the optical colonoscopy group than in the CTC group (2,434 vs 561).