Objective  To compare endoscopic morphologic characteristics and pathologic types of colorectal polyps between gas and water injection colonoscopies.

  Methods  Using the magnifying endoscopy narrow-band imaging (NBI) mode in 62 cases of gas injection colonoscopy and 53 cases of water injection colonoscopy for colorectal polyps in Fujian Provincial Cancer Hospital, the pathologic changes in vascular morphology and surface structure, application of international colorectal endoscopic classification (NICE) pathologic types, real-time prediction, and NBI endoscopic and pathologic histology diagnosis results were analyzed. Furthermore, the sensitivity, accuracy, and detection rates of flat polyps (Paris type 0-IIa) for both procedures were compared.

  Results  The detection rate of flat polyps in the water injection group was 44.64%, and the detection rates of the left and right hemicolon were 26.78% and 17.86%, respectively. The detection rate of flat polyps in the gas injection group was 40.00%, and the detection rates of the left and right hemicolon were 35.56% and 4.44%, respectively. The difference in detection rates between the two groups was statistically significant. The diagnostic sensitivity, specificity, and accuracy of overall NICE classification for colorectal neoplastic lesions were 91.95%, 96.61%, and 93.84%, respectively. The sensitivity, specificity, and accuracy of the gas injection enteroscopy group were 90.74%, 97.27%, and 93.33%, respectively, and those of the water injection enteroscopy group were 93.93%, 95.65%, and 94.64%, respectively. Two cases of sessile serrated adenoma were also found. There was no statistically significant difference in the examination results between the two groups.

  Conclusions  The accuracy of gas or water injection colonoscopy did not significantly differ in predicting the pathologic types of colorectal polyps. However, water injection colonoscopy can improve the detection of 0-IIa polyps in the right colon.