CT colonography can’t compete with colonoscopy on some high-risk polyps

Polyps characterized as both sessile and serrated lead to as many as 30 percent of all colorectal cancers, and they’re very good at avoiding detection by CT colonography—while quite readily giving themselves up to colonoscopy—according to a study published earlier this spring in the American Journal of Gastroenterology.

Joep Ijspeert, MD, of the University of Amsterdam in the Netherlands and colleagues compared the performance of the two modalities as applied to population screening for high-risk sessile serrated polyps (SSPs) in average-risk individuals.

Patients diagnosed by CT colonography with a lesion at least 10 millimeters in size were referred for colonoscopy.

Those with lesions of six to nine millimeters were offered surveillance CT colonography followed by colonoscopy when a lesion of six millimeters or more was detected.

The researchers aggregated data from both groups to mimic American College of Radiology CT colongraphy referral recommendations.

Of 8,844 patients invited to participate, 1,276 colonoscopy and 982 CT colonography invitees agreed.

In the colonoscopy arm, 4.3 percent of individuals were diagnosed with one or more high-risk SSP lesions, compared with 0.8 percent in the CT colonography arm, the authors report.

In total, 3.1 percent of patients in the colonoscopy arm were diagnosed with high-risk SSPs as the most advanced lesion, compared with 0.4 percent in the CTC arm.  

And the current CT colonography strategy yielded markedly lower detection for especially flat high-risk SSPs (17 vs. 0), high-risk SSP located in the proximal colon (32 vs. 1) and SSPs with dysplasia (30 vs. 1).

In their discussion, Ijspeert and team conclude that these shortcomings of CT colonography as compared with colonoscopy “might have implications for the value of CT colonoscopy as a primary colorectal cancer screening tool in opportunistic screening.”

They add that results from other large screening cohorts are needed “to elaborate our findings and to determine the performance of CT colonography in the detection of advanced neoplasia, including high-risk SSPs, compared with the performance of colonoscopy, both in an opportunistic as well as a population-based screening setting taking into account other variables such as participation.”