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Some studies have found that computed tomography colonography (CTC) detects large adenomas (≥1 cm) as effectively as standard optical colonoscopy (OC). But, results for polyps 6–9 mm have been more variable, and radiologists typically do not attempt to read polyps ≤5 mm.
To investigate the relative impact of CTC and OC on subcentimeter polyp detection and resection, investigators compared the yield of subcentimeter adenomas from 1700 OC tests and 1307 CTC tests of average-risk patients referred by the same group of primary care providers to the University of Wisconsin health center.
Results were as follows:
Subcentimeter adenomas were detected in more patients in the OC group than in the CTC group (18.1% vs. 2.7%; P<0.001). This difference was attributed mostly to the higher rate of detection of adenomas ≤5 mm in the OC group (10.3% vs. 0.4%; P<0.001), although the rate of detection of adenomas 6–9 mm was also greater in the OC group (7.8% vs. 2.2%; P<0.001).
Detection of subcentimeter advanced lesions was similar in the OC and CTC groups (0.7% and 0.3%).
Detection of nonadenomatous subcentimeter polyps was more common in the OC group (27.1% vs. 4.1%; P<0.001).
Resection of subcentimeter adenomas was more common in the OC group than in the CTC group (P<0.001).
Resection of advanced subcentimeter lesions was similar in the two groups.
Benson M et al. A comparison of optical colonoscopy and CT colonography screening strategies in the detection and recovery of subcentimeter adenomas. Am J Gastroenterol 2010 Sep 14; [e-pub ahead of print]. (http://dx.doi.org/10.1038/AJG.2010.362)
Comment
These findings show that the rates of detection and resection of subcentimeter adenomas are significantly lower with CTC than with OC. However, the clinical consequences of this difference are uncertain. The authors' statement that about two thirds of screening tests conducted at the University of Wisconsin are still done by colonoscopy is notable, given the renowned expertise in CTC at this center. In a prior study from the University of Wisconsin, the authors suggested that referring physicians were concerned by the extracolonic findings and radiation risk for patients undergoing screening CTC (N Engl J Med 2007; 357:1403). The CTC approach of not resecting subcentimeter adenomas is likely a concern for some referring physicians, but whether that concern is warranted is unknown.