What does sigmoidoscopy really miss?: Lewis JD, Kimmie NG, Hung KE, et al., Detection of proximal adenomatous polyps with screening sigmoidoscopy—a systematic review and meta-analysis of screening colonoscopy, Arch Intern Med 2003;163:413–20

Abstract

The relative effectiveness of flexible sigmoidoscopy compared with colonoscopy to screen for colorectal cancer depends on the magnitude of the association between findings in the proximal and distal colon and the false-negative rate of screening sigmoidoscopy for proximal neoplasia. Lewis et al. performed a systematic review and meta-analysis of screening colonoscopy studies. Published studies through July 31, 2000 of asymptomatic patients undergoing screening colonoscopy were identified from the MEDLINE database. The authors generated pooled estimates of the odds ratio for the association between findings in the distal and proximal colon and the prevalence of isolated proximal adenomatous neoplasia. With the sigmoid–descending colon junction used to identify the beginning of the distal colon, the pooled odds ratio for the association between distal adenomatous polyps and any proximal neoplasia was 2.40 (95% confidence interval [Cl] = 1.42–4.05). Diminutive distal adenomatous polyps were also associated with proximal neoplasia (odds ratio = 2.36; 95% CI = 1.30–4.29). Distal hyperplastic polyps were not associated with proximal neoplasia (odds ratio = 1.44; 95% CI = 0.79–6.62). The prevalence of isolated advanced proximal neoplasia in the three studies was 2%, 3%, and 5%, respectively. When the sigmoid–descending colon junction is used to identify the beginning of the distal colon, this yields a pooled estimate of isolated proximal neoplasia of 16.3% (95% CI = 13.6%–19.1%). Distal adenomatous polyps, including diminutive distal adenomatous polyps, are associated with an increasing prevalence of synchronous proximal neoplasia. From 2% to 5% of patients undergoing screening colonoscopy might have isolated advanced proximal neoplasia.