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H Ergaiey, A Rostom

Division of Gastroenterology, University of Ottawa, Ottawa, Ontario

BACKGROUND & AIM: Previous studies have looked at the effectiveness of performing flexible sigmoidoscopy (FS) versus a full colonoscopy for detection of colorectal neoplasia. However, when comparing the yield of these two procedures, many of these studies assumed that the yield of FS to be the “last” 60 cm of the colonoscopy and often estimated “on the way out”. This assumption may be problematic since the ability to remove a loop and accordion the bowel may differ between the two modalities. The aim of our study is to determine how much colonoscopy overestimates the yield of 60 cm FS.

METHODS: Consecutive patients who were referred for colonoscopy and mucosal biopsy for chronic diarrhea were included in the study and underwent full colonoscopy. On the way in we used proper techniques to ensure that minimal looping was introduced, and a set of left colon biopsies were taken at 60 cm. Upon reaching the cecum, the terminal ilial and colonic mucosa was visualized and biopsied as per standard of care during withdrawal of the scope. The new level of the biopsy marks that were taken at 60 cm on the “way in” was noted and recorded. A one sample T-test was used to compare the new position of the 60 cm mark on the “way out” compared to the original 60 cm position on the “way in”.

RESULTS: Twenty-four subjects (mean age 49.5) had a complete colonoscopy with biopsies taken at 60 cm “on the way in”. The Mean measure of the 60 cm mark on the way out was 37.5 cm (95% CI: 35.0-40.0 cm). The absolute range extended from a minimum of 30 cm to a maximum of 50 cm. The mean difference between 60 cm “on the way in” vs “on the way out” was 22.5 cm (95% CI: 20.07-25.01). This difference reached statistical significance (P <0.001).

CONCLUSIONS: Colonoscopy overestimates the expected colon surface seen with a standard 60 cm FS. This overestimation maybe by as much as 37% and likely occurs since insertion of a scope beyond the reach of a 60 cm FS allows greater loop reduction and “accordioning” of the bowel than with the shorter 60 cm scope. We therefore caution that the yield of sigmoidoscopy in actual practice may be lower than predicted by studies that used colonoscopy as a surrogate for sigmoidoscopy. This study is ongoing.

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