Evaluation of factors associated with en bloc colonic underwater endoscopic mucosal resection

Underwater endoscopic mucosal resection (UEMR) is a relatively simple and safe method for resecting sessile colorectal polyps without a submucosal injection. Only around 1000 UEMRs have been reported in a few studies, and none of the previous studies directly evaluated the factors associated with a successful en bloc resection. We retrospectively evaluated the factors associated with a successful en bloc resection using UEMR from 160 patients between August 2015 and November 2017. Of 173 polyps removed with UEMR, 141 polyps (81.5%) were removed en bloc. Univariable analysis showed that polyp size ≥20 mm (OR: 0.047, 95% CI: 0.014‐0.162, P  < .001), prior treatment (OR: 0.297, 95% CI: 0.135‐0.655, P  = .003), and polyp morphology (flat vs sessile) (OR: 0.111, 95% CI: 0.025‐0.482, P  = .003) were the significant factors for en bloc resection. Multivariate analysis showed that polyp size ≥20 mm (OR: 0.053, 95% CI: 0.015‐0.194, P  < .001), prior treatment (OR: 0.313, 95% CI: 0.118‐0.832, P  = .020), and polyp morphology (flat vs sessile) (OR: 0.095, 95% CI: 0.019‐0.469, P  = .004) were still significant. The rate of adverse events was 3.5% ( n  = 6) and included delayed hemorrhages ( n  = 2, 1.2%), muscle defects requiring endoscopic clipping ( n  = 3, 1.7%), and delayed perforations ( n  = 1, 0.6%). Polyp size < 20 mm, without prior treatment, and sessile polyp morphology were significantly associated with en bloc UEMR.