Background and study aims: Narrow band imaging (NBI) can accurately characterize colonic polyps using microvascular appearances. We aimed to assess whether the Kudo pit pattern classification is accurate when used with NBI (without dye-spray), and if microvascular appearances or NBI pit patterns maintain accuracy for polyp characterization at sizes < 10 mm.
Patients and methods: 116 polyps < 10 mm in size were detected in 62 patients undergoing surveillance colonoscopy. The polyps were prospectively assessed using NBI and magnification for Kudo pit pattern (III-V neoplastic, I-II non-neoplastic) and vascular pattern intensity (VPI), a measure of microvascular density (strong VPI, neoplastic; normal or weak VPI, non-neoplastic). Sensitivity, specificity, and accuracy were calculated and compared with results from histopathology.
Results: The mean polyp size was 3.4 mm (range 1 - 9 mm). Overall, NBI pit pattern sensitivity, specificity, and accuracy were 0.88, 0.91, and 89.6 %, respectively. Equivalent values for VPI were 0.94, 0.89, and 91.4 %. Results were similar when polyps were subdivided into diminutive polyps (size <or= 5 mm) and flat polyps. Combining both pit pattern and VPI improved the sensitivity (0.98, P = 0.06 versus NBI pit pattern alone). There was very good agreement between NBI pit pattern and VPI for prediction of dysplasia (kappa = 0.83). No evidence of a learning curve for VPI was found. The NBI pit pattern was better than the VPI at subclassifying hyperplastic from other non-neoplastic polyps (sensitivity 0.79 versus 0.56, respectively, P = 0.02), but accuracy was poor.
Conclusion: The NBI pit pattern and VPI are both highly accurate in characterizing neoplastic colonic polyps of < 10 mm, with VPI appearing to be simple to learn. NBI has the potential to replace conventional histology for small polyps.