Comparison of Underwater vs Conventional Endoscopic Mucosal Resection of Intermediate-Size Colorectal Polyps

Gastroenterology. 2019 Aug;157(2):451-461.e2. doi: 10.1053/j.gastro.2019.04.005. Epub 2019 Apr 11.


Background & aims: Endoscopic mucosal resection (EMR) with submucosal injection is an established method for removing colorectal polyps, although the en bloc resection rate decreases when polyp size exceeds 10 mm. Piecemeal resection increases local recurrence. Underwater EMR (UEMR) is an effective technique for removal of sessile colorectal polyps and we investigated whether it is superior to conventional EMR (CEMR).

Methods: We conducted a multicenter randomized controlled trial at 5 institutions in Japan. Patients with endoscopically diagnosed, intermediate-size (10-20 mm) sessile colorectal lesions were randomly assigned to undergo UEMR or CEMR. Only the most proximal lesion was registered. The UEMR procedure included immersion of the entire lumen in water and snare resection of the lesion without submucosal injection of normal saline. We analyzed outcomes of 108 colorectal lesions in the UEMR group and 102 lesions in the CEMR group. R0 resection was defined as en bloc resection with a histologically confirmed negative resection margin. The primary endpoint was the difference in the R0 resection rates between groups.

Results: The proportions of R0 resections were 69% (95% confidence interval [CI] 59%-77%) in the UEMR group vs 50% (95% CI 40%-60%) in the CEMR group (P = .011). The proportions of en bloc resections were 89% (95% CI 81%-94%) in the UEMR group vs 75% (95% CI 65%-83%) in the CEMR group (P = .007). There was no significant difference in median procedure time (165 vs 175 seconds) or proportions of patients with adverse events (2.8% in the UEMR group vs 2.0% in the CEMR group).

Conclusions: In a multicenter randomized controlled trial, we found that UEMR significantly increased the proportions of R0 resections for 10- to 20-mm sessile colorectal lesions without increasing adverse events or procedure time. Use of this procedure should be encouraged. Trials registry number: UMIN000018989.

Keywords: Colon; Efficacy; Endoscopy; Large.

Publication types

  • Comparative Study
  • Multicenter Study
  • Randomized Controlled Trial
  • Video-Audio Media

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Colon / diagnostic imaging
  • Colon / pathology
  • Colon / surgery
  • Endoscopic Mucosal Resection / adverse effects
  • Endoscopic Mucosal Resection / methods*
  • Female
  • Humans
  • Intestinal Mucosa / diagnostic imaging
  • Intestinal Mucosa / pathology*
  • Intestinal Mucosa / surgery
  • Intestinal Polyps / diagnostic imaging
  • Intestinal Polyps / pathology
  • Intestinal Polyps / surgery*
  • Japan
  • Male
  • Middle Aged
  • Operative Time
  • Postoperative Complications / epidemiology*
  • Postoperative Complications / etiology
  • Rectum / diagnostic imaging
  • Rectum / pathology
  • Rectum / surgery
  • Secondary Prevention / methods*
  • Treatment Outcome
  • Water


  • Water