Background/Aims: Narrow band imaging (NBI) is an optical endoscopic technique for predicting polyp histology during colonoscopy. However, it has not been elucidated the impact of polyp characteristics on the diagnostic capabilities of NBI. We aimed to evaluate which polyp characteristics can influence the diagnostic accuracy of NBI for discriminating neoplastic from non-neoplastic colorectal polyps. Methodology: A total of 232 colorectal polyps from 134 patients undergoing screening or surveillance colonoscopy were retrospectively analyzed. White light imaging (WLI) and NBI images of polyps were assessed by two experienced endoscopists and two trainees and then compared with histopathology. Results: When classified according to polyp morphology, NBI as well as WLI had a significantly lower sensitivity and diagnostic accuracy for non-polypoid lesions than for polypoid lesions in both experienced and trainee groups. In contrast, the specificity of NBI and WLI for non-polypoid lesions was higher than that for polpyoid lesions. As for polyp size, the diagnostic accuracy of NBI for polyps ≤5mm was significantly lower than for polyps of 6 to 9mm or ≤10mm in the experienced group. Conclusions: NBI had a significantly lower diagnostic accuracy for predicting polyp histology in non-polypoid or diminutive colorectal lesions.
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