The association between distal and proximal colorectal adenomas is undefined, and no preventive guidelines explicitly recommend colonoscopic examination for proximal lesions when a distal adenoma is found on sigmoidoscopic examination. Dave and colleagues performed a systematic review to determine the absolute risk of synchronous proximal neoplasia in the presence of distal hyperplastic polyps. They also measured the relative risk of proximal neoplasia associated with distal hyperplastic polyps compared with no polyps and with distal adenomatous polyps.

The authors performed a MEDLINE and EMBASE search of studies using proximal neoplasia and advanced neoplasia as outcome variables. Twelve screening studies and six case-finding studies were found. In the latter, colonic evaluation was performed because of the presence of risk factors or symptoms.

In the screening studies, proximal neoplasia was present in 16 percent of persons with no distal polyps, in 25 percent of those with distal hyperplastic polyps, and in 36 percent of those with distal adenomatous polyps. In a comparison subset of persons with no distal polyps, the absolute risk of finding proximal neoplasia was 21 percent for distal hyperplastic polyps and 40 to 47 percent for distal adenomatous polyps, while the relative risk was 1.3 and 2.5, respectively. Among all 12 screening studies, the risk of proximal neoplasia in persons with distal adenomatous polyps was 1.5 compared with distal hyperplastic polyps.

For case studies, the pooled absolute risk of proximal neoplasia in association with distal hyperplastic polyps was 35 percent. The prevalence of proximal neoplasia in persons with distal adenomatous polyps ranged from 30 to 51 percent, while the prevalence in those with no distal polyps varied from 3 to 23 percent.

The authors conclude that persons with distal hyperplastic polyps have a risk of proximal neoplasia that is intermediate between those persons with no distal polyps and those with distal adenomas. The risk of proximal neoplasia associated with distal hyperplastic polyps was lower in asymptomatic persons who underwent colonoscopy after screening sigmoidoscopy compared with those who underwent diagnostic colonoscopy for symptoms or risk factors for colorectal neoplasia. Clinically, this conclusion does not lead to recommendations for colonoscopic examination for all distal polyps. Further understanding of the neoplastic potential of distal hyperplastic polyps is necessary before deciding who requires colonoscopy after sigmoidoscopy.