Sigmoidoscopy, is it Enough as a Screening Tool? -Undetectable colorectal adenomas by sigmoidoscopy-

ABSTRACT

BACKGROUND: It is generally accepted that most colorectal cancers develop from adenomas, so the detection and removal of them can reduce the incidence of colorectal cancers. Sigmoidoscopy is the effective tool for detecting and removing adenomatous polyps in the rectosigmoid region, but its major limitation is that sigmoidoscopy alone can not detect considerable portion of colorectal adenomas. METHODS: From October, 1996 to August, 1997, we performed 2017 sigmoidoscopies and 1683 colonoscopies. We analysed the anatomical distribution of adenomas and compared the detection rate of adenomas between two groups. In 32 cases, adenomas detected by sigmoidoscopy were followed by colonoscopy in less than 2 months. RESULTS: We found 125 cases of adenomas in 2017 sigmoidoscopies and 281 cases of adenomas in 1683 colonoscopies. In 281 cases of adenomas found by colonoscopy, 151 cases had rectosigmoid adenomas only and 25 cases had rectosigmoid and proximal adenomas, 105 cases had proximal adenomas only. The detection rate of adenomas by sigmoidoscopy was significantly lower than that by colonoscopy in the rectosigmoid region(6.1% vs. 10.5%, p=0.002). In 32 cases of adenomas found by sigmoidoscopy that were followed by colonoscopy, 7 cases of proximal adenomas and 6 cases of additional rectosigmoid adenomas were detected. CONCLUSION: Sigmoidoscopy cannot detect adenomas in the proximal colon beyond the sigmoid, it also can miss a significant portion of adenomas in the rectosigmoid.