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Small and Diminutive Polyps Detected at Screening CT Colonography: A Decision Analysis for Referral to Colonoscopy

¹ Department of Radiology, University of Wisconsin Medical School, E3/311 Clinical Science Center, 600 Highland Ave., Madison, WI 53792-3252.
² Department of Radiology, Uniformed Services University of the Health Sciences, Bethesda, MD.
³ Gastroenterology and Digestive Endoscopy Unit, "Nuovo Regina Margherita" Hospital, Rome, Italy.
⁴ Department of Radiological Sciences, "Sapienza" - University or Rome, Polo Pontino, I.C.O.T. Hospital, Latina, Italy.
⁵ Department of Radiological Sciences, University of Rome La Sapienza "Policlinico Umberto I," Rome, Italy.

OBJECTIVE. The objective of this study was to assess the clinical and economic impact of colonoscopic referral for small and diminutive polyps detected at CT colonography (CTC) screening.

MATERIALS AND METHODS. A decision analysis model was constructed incorporating the expected polyp distribution, advanced adenoma prevalence, colorectal cancer (CRC) risk, CTC performance, and costs related to CRC screening and treatment. The model conservatively assumed that CRC risk was independent of advanced adenoma size. The number of diminutive ( 5 mm), small (6-9 mm), and large ( 10 mm) CTC-detected polyps needed to be removed to detect one advanced adenoma or prevent one CRC over a 10-year time horizon was calculated. The cost-effectiveness of polypectomy was also assessed.

RESULTS. The estimated 10-year CRC risk for unresected diminutive, small, and large polyps was 0.08%, 0.7%, and 15.7%, respectively. The number of diminutive, small, and large polyps needed to be removed to avoid leaving behind one advanced adenoma was 562, 71, and 2.5, respectively; similarly, 2,352, 297, and 10.7 polypectomies would be needed, respectively, to prevent one CRC over 10 years. The incremental cost-effectiveness ratio of removing all diminutive and small CTC-detected polyps was $464,407 and $59,015 per life-year gained, respectively. Polypectomy for large CTC-detected polyps yielded a cost-saving of $151 per person screened.

CONCLUSION. For diminutive polyps detected at CTC screening, the very low likelihood of advanced neoplasia and the high costs associated with polypectomy argue against colonoscopic referral, whereas removal of large CTC-detected polyps is highly effective. The yield of colonoscopic referral for small polyps is relatively low, suggesting that CTC surveillance may be a reasonable management option.

Keywords: colorectal cancer • colorectal polyps • CT colonography • CT colonography screening • health care costs