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CT Colonography Is Equal to Colonoscopy for Detecting Advanced Adenomas

Whether CTC is the better test for screening overall still is unclear.

Computed tomographic colonography (CTC) is a potential alternative to optical colon imaging for screening purposes. In a study from Madison, Wisconsin, the yield of CTC that was performed for screening in 3120 consecutive adults (mean age, 57) was compared with primary optical colonoscopy (OC) in 3163 similar consecutive adults. (The study was not randomized.) Patients were referred for OC after CTC if CTC identified any polyps 10 mm or 3 smaller (6–9 mm) polyps. Patients with one or two smaller polyps were offered same-day OC and polypectomy or follow-up CTC surveillance at 3 years.

During CTC, 123 advanced neoplasms (including 12 cancers) were found; during OC screening, 121 advanced neoplasms (including 4 cancers) were found. About 8% of CTC screenings resulted in referrals for OC. Proven advanced neoplasia was found in 3.4% of the OC group and in 3.2% of the CTC group (this percentage did not include 158 patients with 193 unresected CTC-detected smaller polyps who opted for surveillance). The total numbers of polypectomies in the CTC and OC groups were 561 and 2434, respectively. Seven perforations occurred in the OC group during screening, and none occurred in the CTC group.

Comment: The researchers reported the numbers of cancers and advanced adenomas detected in the two arms, as well as the number of polypectomies performed, but not the total number of adenomas detected. If advanced adenomas are the target of colorectal cancer screening, then these results support CTC as equal to OC as a primary screening method. In fact, the authors suggest CTC as a filter for OC therapy, because only 8% of patients who underwent CTC required OC follow-up procedures. The negligible perforation rate for CTC favors its inclusion as an option for primary screening.

The nonrandomized design of this study is problematic. The higher rate of cancer in the OC group suggests that the study populations were different: Perhaps a higher percentage of patients in the OC group had received previous negative screening test results — such testing would have selected for a lower rate of cancers and advanced adenomas in the OC group. Another potential explanation for a lower cancer rate in the OC group is that the quality of the colonoscopies was substandard. Indeed, evaluating the overall quality of the colonoscopies is difficult, because the overall rates of adenoma detection were not provided, and current recommendations for screening colonoscopy are based on overall adenoma detection rates. Finally, the rate of perforation in the OC arm was twice what is expected in a screening population. Thus, we need additional information to interpret this nonrandomized comparison before we can generalize the results to clinical practice.

— Douglas K. Rex, MD

Published in Journal Watch Gastroenterology October 3, 2007

Citation(s):

Kim DH et al. CT colonography versus colonoscopy for the detection of advanced neoplasia. N Engl J Med 2007 Oct 4; 357:1403.

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