Narrow Band Imaging (NBI) Influences the Learning Curve for Conventional Endoscopy - Final Results of a Prospective Randomized Study in the Detection of Colorectal Adenomas

Background: Results concerning staining and the use of the novel technology of narrow band imaging for the detection of colorectal adenomas are conflicting. It is well known from tandem colonoscopy studies that 15-20% of - mostly small - adenomas are missed. Staining has been proposed to increase the yield of especially flat adenomas, and intermediate results of Narrow Band Imaging (NBI), a new technique using different light filtering to increase contrast, have been encouraging with significantly more adenomas been found. Methods: Consecutive patients presenting for diagnostic colonoscopy with symptoms (pos. hemoccult, pain, diarrhea), for surveillance after polypectomy or for screening (cases with known tumors or IBD were excluded) were randomly allocated to NBI or conventional colonoscopy (Olympus Corp., Hamburg, Germany) according to availability of the instrument. The instrument was introduced as usual and on withdrawal from the cecum the control group (C) was examined conventionally with the NBI function not being activated, whereas the study group (NBI) was examined with NBI exclusively, with an option to switch back to normal imaging in case of uncertainty. These instances however were recorded and the reasons given. Polyp detection rate including polyp details as well as withdrawal time were recorded in both groups. Results: 401 patients (53% male, mean age 59 years) have been included; 5 cases with cancers were found but are excluded from this analysis. The overall rates of adenomas and hyperplastic polyps found were 19.7% and 19.9%, respectively. In the NBI group adenomas were detected in 22.7% compared to 16.7% in the control group, but this difference was statistically not significant (p = 0.129), neither in the entire group nor in any of the various subgroups (location, size, form). The number of colonoscopies to be performed to find one additional patient with adenoma would be 17 on the basis of the present adenoma difference. However, when comparing the first and the last 100 cases of the study, an initial significant different in adenoma rates ((NBI 26%, controls 8%, p = 0.015) was not sustained in the last 100 cases (27% vs. 19%, P = 0.33). Hyperplastic polyps were found more frequently in the NBI group than in controls (28.3% and 11.66%, p < 0.001). Conclusions: The new technique of NBI seems enhances the polyp detection rate in a high risk population, but this effect was present for adenomas only in the initial study period. Since the percentage of adenomas found in the control group increased with this rate being stable in the control group, a learning effect from NBI for conventional endoscopy could be postulated.