The water exchange (WE) colonoscopy method significantly improves detection of missed adenomas, especially those in the proximal colon or with flat shapes, in patients undergoing selective polypectomy, according to the results of a study published in Digestive and Liver Disease.

Researchers sought to determine whether the WE method could increase the detection of missed adenomas compared with standard air-insufflated (AI) colonoscopy. Patients aged 18 to 80 years who had polyps identified during index colonoscopy (AI method) and who underwent selective polypectomy within 6 months were eligible for the prospective, patient-blinded, randomized controlled trial. The primary end point was the adenoma miss rate (AMR), which was defined as the number of patients with 1 or more additional adenomas during the polypectomy procedure divided by the total number of patients in each group.

The investigators included 450 patients in the trial, with 225 in each procedure group. The mean age of the cohort was 55 years, and the median number of polyps found in the index colonoscopy was 2. The time interval from index colonoscopy to polypectomy was approximately 2.5 months.

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A total of 933 adenomas were detected and resected, of which 300 were newly detected. The AMRs were 45.8% (103/225) in the WE group and 35.6% (80/225) in the AI group (P = .035), and the average numbers of missed adenomas were 0.76 and 0.58, respectively.

A higher proportion of patients in the WE group had at least 1 missed adenoma in the proximal colon (38.2% vs 24.4%, P = .002). The adenoma-level miss rate was also higher among WE group participants (35.1% vs 29.0%, P = .036). The ratio of missed advanced adenoma between the 2 groups was comparable.

The proximal polyp miss rate was higher in the WE group than in the AI group (47.6% vs 36.9%, P = .028). The polyp-level miss rate was also higher in the WE group (41.1% vs 34.2%, P = .006). A subgroup analysis found that patients in the WE group had more missed adenomas located in the proximal colon or with flat shapes.

“The improved detection of missed adenomas located in the proximal colon by the WE method may be clinically important,” stated the study authors. “These adenomas are more likely to be at high risk for interval colorectal cancer, as reported in previous studies.”

The researchers noted that their study had 2 limitations: the endoscopists were not blinded owing to the different insertion methods, and the study was conducted in a single tertiary center.

“This study confirmed that cecal intubation was necessary, and WE colonoscopy could find more missed adenomas than traditional air colonoscopy in patients admitted for polypectomy,” the investigators concluded. “Missed adenomas located in the proximal colon or with flat shapes were more frequently detected in the WE group. WE colonoscopy could also obtain better bowel preparation quality and patient pain scores. At the same time, WE colonoscopy did not significantly increase the total procedure time and complications; thus, it could be a more effective and safe choice for endoscopic polypectomy for inpatients.”


Ren G, Wang X, Luo H, et al. Effect of water exchange method on adenoma miss rate of patients undergoing selective polypectomy: a randomized controlled trialDig Liver Dis. Published online December 31, 2020. doi:10.1016/j.dld.2020.11.012