Screening Colonoscopy and the Right Side of the Colon

By William B. Ershler, MD

Abstract & Commentary

Synopsis: In an analysis of community-performed colonoscopies in southwestern Germany, the prevalence of left-sided advanced colorectal neoplasms, but not right-sided neoplasms, was strongly reduced within a ten-year period after colonoscopy.

Source: Brenner H, et al. Protection from right- and left-sided colorectal neoplasms after colonoscopy: Population-based study. J Natl Cancer Inst. 2010;102:89–95.

Screening colonoscopy is a well-established method for reducing the risk of death from colorectal cancer. The National Polyp Study1 demonstrated colonoscopy to be associated with a 76% to 90% risk reduction for colorectal cancer among people with colorectal polyps. The curious clinical observation has been made that a greater proportion of colorectal cancer is right sided among those who have had a previous colonoscopy when compared to the general population.2,3 This raises the possibility that colonoscopy is more effective in detecting and removing left-sided colonic lesions. Yet, evidence on the magnitude of overall protection, and protection according to anatomical site through colonoscopy, performed in the community setting is sparse.

To address this, Brenner et al from southwestern Germany assessed whether receiving a colonoscopy in the preceding 10-year period, compared with no colonoscopy, was associated with prevalence of advanced colorectal neoplasms (defined as cancers or advanced adenomas) at various anatomical sites. They performed a statewide cross-sectional study among 3,287 participants in screening colonoscopy between May 1, 2005, and December 31, 2007, from the state of Saarland in Germany, who were aged 55 years or older. Prevalence of advanced colorectal neoplasms was ascertained by screening colonoscopy and histopathologic examination of any polyps excised. Previous colonoscopy history was obtained by standardized questionnaire, and its association with prevalence of advanced colorectal neoplasms was estimated, after adjustment for potential confounding factors.

Advanced colorectal neoplasms were detected in 308 (11.4%) of the 2,701 participants with no previous colonoscopy, compared with 36 (6.1%) of the 586 participants who had undergone colonoscopy within the preceding 10 years. After adjustment, overall and site-specific adjusted prevalence ratios for previous colonoscopy in the previous 10-year period were as follows: Overall, 0.52 (95% confidence interval [CI] = 0.37 to 0.73); cecum and ascending colon, 0.99 (95% CI = 0.50 to 1.97); hepatic flexure and transverse colon, 1.21 (95% CI = 0.60 to 2.42); right-sided colon combined (cecum to transverse colon), 1.05 (95% CI = 0.63 to 1.76); splenic flexure and descending colon, 0.36 (95% CI = 0.16 to 0.82); sigmoid colon, 0.29 (95% CI = 0.16 to 0.53); rectum, 0.07 (95% CI = 0.02 to 0.40); left colon and rectum combined (splenic flexure to rectum), 0.33 (95% CI = 0.21 to 0.53).

Commentary

Thus, the prevalence of left-sided advanced colorectal neoplasms, but not right-sided advanced neoplasms, was strongly reduced within a 10-year period after colonoscopy. The findings are notable because endoscopies were performed at community sites and may more accurately reflect results for the majority of individuals who are screened outside of a tertiary referral center or on a clinical trial.

An explanation for the lack of colonoscopy efficacy for protecting from right sided cancers is not immediately clear. It may simply be technical (i.e., the result of less than adequate preparation or the greater difficulty of reaching all the way to the cecum in some cases). However, it's also possible that because adenomas are different on the right side, and more likely to be sessile or flat, they may, thus, be more likely to be missed or excised.4 However, to the extent that these technical factors are modifiable, enhanced efforts should be undertaken to improve colonoscopy results. In the meantime, clinicians should be aware that although colonoscopy is highly effective in preventing death from colorectal cancer, it is primarily from left-sided lesions that this effect is realized. A prior "negative" screening colonoscopy does not preclude the appearance of colon cancer, particularly on the right side.

References

1. Winawer SJ, et al. Prevention of colorectal cancer by colonoscopic polypectomy. The National Polyp Study Workgroup. N Engl J Med. 1993;329:1977-1981.

2. Farrar WD, et al. Colorectal cancers found after a complete colonoscopy. Clin Gastroenterol Hepatol. 2006;4:1259-1264.

3. Singh H, et al. Risk of developing colorectal cancer following a negative colonoscopy examination: evidence for a 10-year interval between colonoscopies. JAMA. 2006;295:2366-2373.

4. Heresbach D, et al. Miss rate for colorectal neoplastic polyps: a prospective multicenter study of back-to-back video colonoscopies. Endoscopy. 2008;40: 284-290.