Prevalence of proximal adenomas after an adenoma is found on flexible sigmoidoscopy

Background: Adenomatous polyps are a precursor of colorectal cancer and a frequent finding on screening flexible sigmoidoscopy (FS). Performance of colonoscopy when a diminutive (<6 mm) adenoma is found on FS has been the subject of considerable debate. Methods: We retrospectively reviewed the data from our colorectal cancer screening program for patients with adenoma(s) found on FS. Patients were divided into three groups based on FS findings: (1) an adenoma <6 mm in size, (2) multiple non-advanced adenomas or an adenoma 6–10 mm in size, or (3) advanced adenoma defined as an adenoma >10 mm or with villous histology or high-grade dysplasia or cancer. A comparison of the proximal findings was then made. Results: 5291 FS reports were reviewed with 606 (12%) patients having at least one adenoma. Colonoscopy reports were available in 550 patients. Of the 258 patients with a diminutive distal adenoma, 69 (27%) had a proximal adenoma and 13 (5%) had an advanced proximal adenoma on colonoscopy. Of the 164 patients with an adenoma 6–10 mm or multiple non-advanced adenomas, 59 (36%) had a proximal adenoma and 13 (8%) had an advanced proximal adenoma. Of the 128 patients with a distal advanced adenoma, 58 (45%) had a proximal adenoma and 15 (12%) had an advanced proximal adenoma. The increase in proximal adenomas across the three groups was significant (P=0.001), and there was a trend for increased prevalence of advanced adenomas (P=0.061). Conclusions: The prevalence of proximal adenomas increased significantly with more advanced lesions found distally at FS, and there was a trend towards a higher prevalence of advanced proximal adenomas. Based on current guidelines, flexible sigmoidoscopy is a screening option that can be used to identify average-risk patients at increased risk of proximal neoplasia.