As part of the National Polyp Study, colonoscopic examination and barium enema were compared in paired surveillance examinations in those who had undergone a prior colonoscopic polypectomy. The proportion of examinations in which adenomatous polyps were detected by barium enema was related to the size of the adenoma (P = .009); the rate was 32% for colonoscopic examinations in which the largest adenomas detected were no larger than 5 mm, 53% for those in which the largest adenomas detected were 6 mm to 10 mm, and 48% for those in which the largest adenomas detected were larger than 10 mm. In patients who have undergone colonoscopic polypectomy, colonoscopic examination is a more sensitive method of surveillance than double-contrast barium enema.
Because there are no RCTs of colonoscopy, evidence of benefit is indirect. Most indirect evidence is about detection rate of lesions that may be clinically important (like early CRC or advanced adenomas). Some case-control results are available. One RCT of colonoscopy has been initiated.
Evidence about lesion detection rate
In a colonoscopic study of 3,121 predominantly male U.S. veterans (mean age: 63 years), advanced neoplasia (defined as an adenoma that was ?10.0 mm in diameter, a villous adenoma, an adenoma with high-grade dysplasia, or invasive cancer) was identified in 10.5% of the individuals. Among patients with no adenomas distal to the splenic flexure, 2.7% had advanced proximal neoplasia. Patients with large adenomas (?10.0 mm) or small adenomas (<10.0 mm) in the distal colon were more likely to have advanced proximal neoplasia than were patients with no distal adenomas (OR = 3.4; 90% CI, 1.8-6.5 and OR = 2.6; 90% CI, 1.7-4.1, respectively). One-half of those with advanced proximal neoplasia, however, had no distal adenomas. In a study of 1,994 adults (aged 50 years or older) who underwent colonoscopic screening as part of a program sponsored by an employer, 5.6% had advanced neoplasms. Forty-six percent of those with advanced proximal neoplasms had no distal polyps (hyperplastic or adenomatous). If colonoscopic screening is performed only in patients with distal polyps, about half the cases of advanced proximal neoplasia will not be detected.
A study of colonoscopy in women compared the yield of sigmoidoscopy versus colonoscopy. Among 1,463 women, cancer was found in one woman and advanced colonic neoplasia in 72 women or 4.9% (about one-half the prevalence compared with men). The authors focused, however, on RR (i.e., RR of missing an advanced neoplasm) as the outcome, instead of absolute risk of such neoplasms, which is substantially lower in women. In addition, the natural history of advanced neoplasia is not known, so its importance as an outcome in studies of detection is not clear.