IS COLONOSCOPY INDICATED FOR SMALL ADENOMAS FOUND BY SCREENING FLEXIBLE SIGMOIDOSCOPY

Background: There is controversy over whether patients who have a smal l tubular adenoma on screening flexible sigmoidoscopy should undergo c olonoscopic examination of the proximal colon. Objective: To prospecti vely determine the prevalence of advanced polyps in the proximal colon among patients who have small adenomas on screening sigmoidoscopy. De sign: Prospective cohort study. Setting: A health maintenance organiza tion and a Veterans Affairs medical center. Patients: Asymptomatic pat ients older than 50 years of age who had no risk factors for colon can cer and underwent sigmoidoscopy. Intervention: At the time of sigmoido scopy, all polyps were biopsied and characterized. All patients with d istal adenomas were offered colonoscopy. Measurements: The size and hi stology of polyps identified by sigmoidoscopy and colonoscopy were not ed. Polyps were considered advanced if they were larger than 10 mm or were tubulovillous, villous, or malignant. The prevalence of advanced proximal polyps was determined, and patients were stratified by the si ze and number of distal polyps found by sigmoidoscopy. Results: Among 4490 patients who underwent sigmoidoscopy, a neoplastic lesion was det ected in 401 (8.9%) and colonoscopy was done in 301 (75%). Of 90 patie nts with a single tubular adenoma 1 to 5 mm in diameter in the distal colon, 0% (95% CI, 0.0% to 4.0%) had an advanced proximal polyp compar ed with 5.4% (CI, 2.4% to 10.4%) of those who had multiple distal poly ps 1 to 5 mm or 6 to 10 mm in diameter and 7.9% (CI, 2.6% to 17.6%) of those who had advanced distal polyps (P = 0.013 for trend). The low-r isk group with a single tubular adenoma 1 to 5 mm in diameter represen ted 44% of all patients with distal adenomas or cancers found at flexi ble sigmoidoscopy. Conclusions: Among patients undergoing screening si gmoidoscopy, those with single tubular adenomas of 5 mm or less had a low prevalence of advanced proximal polyps. These patients may not ben efit from colonoscopy.