How Important Is Removing Small Polyps Found on CT Colonography?

With the addition of CT colonography (so-called virtual colonoscopy) to colorectal cancer screening guidelines, there is concern about whether or not to remove small polyps found during the CTC exam.

Large polyps are 10 millimeters or bigger, and doctors agree that people who have at least one large polyp discovered by CT colonography (CTC) should be referred for an optical colonoscopy to have them removed right away.  However, it isn’t clear whether or not small polyps larger than 5 millimeters but not yet 10 millimeters need to be removed.  Because most colorectal polyps develop slowly, it is enough to wait and repeat the CTC test in three years?

Using a decision model that analyzed key information about colorectal cancer risk and development, researchers found that when only small polyps are found, waiting to repeat the CTC in three years has the most benefit with the least risk and cost.

Their analysis included information about polyp and cancer development, colorectal cancer risk and prevalence, CTC effectiveness, CTC costs, and patient risks during optical colonoscopy.  Risks include possible colon perforation.

Analysis showed expected colorectal cancer deaths within five years to be:

• 560 among every 10,000 people in the general screening population who are not screened.
• 3 per 10,000 who had a small (6 -9 mm) polyp found and waited to repeat CTC in three years.
• 2 per 10,000 with small polyps who were referred for an immediate optical colonoscopy to remove them.

So, saving one life from colorectal cancer would require an additional 9,997 colonoscopies with the potential of 10 perforations and an additional cost of over $372,850.

Dr. Perry Pickhardt, radiologist at the University of Wisconsin in Madison, and his colleagues concluded,

For patients with small (6- to 9-mm) polyps detected at CTC screening, the exclusion of large polyps ( 10 mm) already confers a very low risk of colorectal cancer. The high costs, additional complications, and relatively low incremental yield associated with immediate polypectomy of 6- to 9-mm polyps support the practice of 3-year CTC surveillance, which allows for selective noninvasive identification of small polyps at risk.

SOURCE: Pickhard et al., American Journal of Roentgenology, Volume 191, Issue 5, November 2008.