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CT Colonography vs. Colonoscopy

Initial CTC screening performed as well as universal colonoscopy in the detection of advanced neoplasia — and minimized the risk for perforation.

In earlier studies, the accuracy of computed tomographic colonography (CTC) screening has varied compared with conventional colonoscopy. This latest study from the University of Wisconsin compared two groups: In a "primary CTC" group, 3120 people underwent initial CTC screening, and those with polyps of at least 6 mm were offered colonoscopy the same day; in a "primary colonoscopy" comparison group, 3163 people directly underwent colonoscopy. Patients were not randomized but rather were referred by physicians for one procedure or the other. Mean age and male/female ratio were similar in the two groups.

Only 8% of CTC patients proceeded to colonoscopy; thus, many fewer polyps were removed in the primary CTC group than in the primary colonoscopy group (561 vs. 2434). However, the number of advanced adenomas (adenomas 10 mm, and smaller adenomas with villous features or high-grade dysplasia) was similar in the two groups (109 and 117). Invasive cancers were diagnosed in 14 primary CTC patients and 4 primary colonoscopy patients. Colonic perforation occurred in 7 primary colonoscopy patients (4 of whom required surgery), and in no primary CTC patients.

Comment: In this study, initial CTC screening (followed by selective colonoscopy) compared favorably with universal colonoscopy in the detection of advanced neoplasia, and it minimized the risk for perforation. However, CTC patients with only one or two polyps measuring 6 to 9 mm were offered CTC follow-up instead of immediate colonoscopy; for the 5% of CTC patients who accepted this offer, long-term follow-up isn’t yet available. Several other caveats apply. First, the accuracy of CTC will vary from center to center, depending on technique and experience. Second, some authorities have expressed concern about radiation exposure, especially with repeated CTC follow-up studies. And third, it’s unclear whether the incidental identification of extracolonic findings at CTC will confer net benefit or harm in screened populations.

— Allan S. Brett, MD

Published in Journal Watch General Medicine 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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