Background: The need for colonoscopy in patients with adenomas 5 mm or less in diameter that are detected by sigmoidoscopy is controversial.
Methods: We prospectively determined the prevalence of proximal colonic neoplasms in asymptomatic patients at average risk for colorectal cancer, each of whose index lesion on screening fiberoptic sigmoidoscopy was a benign adenoma. Polyps found on sigmoidoscopy underwent biopsy, and colonoscopy was recommended to all patients with neoplastic polyps. Rectosigmoid adenomas were classified as diminutive (< or = 5 mm in diameter), small (6 to 10 mm in diameter), or large (> or = 11 mm in diameter).
Results: Of 3496 consecutive patients referred for sigmoidoscopy, 311 had neoplastic rectosigmoid polyps; 108 of these patients were excluded from the analysis because of a history of colonic neoplasia, symptoms, prior colonic evaluation, or incomplete follow-up data. The remaining 203 patients made up the study group, and all underwent colonoscopy. Neoplasms were found in the proximal colon in 40 of 137 patients (29 percent) with diminutive index polyps, 15 of 52 patients (29 percent) with small index polyps, and 8 of 14 patients (57 percent) with large index polyps. Advanced neoplasms (adenomas > or = 10 mm in diameter, adenomas with a villous component or moderate-to-severe dysplasia, carcinoma in situ, or frank carcinoma) were found in 8 patients (6 percent), 5 patients (10 percent), and 4 patients (29 percent), respectively. Two patients with diminutive index polyps had proximal carcinoma in situ, and two had proximal stage I carcinomas; one patient with a large index polyp had proximal stage III carcinoma.
Conclusions: The substantial prevalence of proximal colonic neoplasms, including advanced lesions, in asymptomatic average-risk patients with rectosigmoid adenomas < or = 5 mm in diameter warrants colonoscopy in these patients.