Underwater versus Conventional Endoscopic Mucosal Resection for Non-Pedunculated Colorectal Lesions: A Randomized Clinical Trial

Published:October 26, 2022DOI:
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      Background and aims

      Conventional endoscopic mucosal resection (CEMR) is the standard modality for removing non-pedunculated colorectal lesions. Underwater endoscopic mucosal resection (UEMR) has emerged as an alternative method. There are few comparative studies between these techniques, especially evaluating recurrence. Then, the purpose of this trial was to compare CEMR and UEMR for the resection of colorectal lesions with respect to efficacy, safety and recurrence rate.


      Randomized controlled trial of UEMR versus CEMR for naïve and non-pedunculated lesions measuring between 10 and 40 mm. The primary outcome was adenoma recurrence at 6 months after the resection. Secondary outcomes were technical success, en bloc resection and adverse events rates. Block randomization was used to assign patients. Tattooing was performed to facilitate localization of the scars and eventual recurrences. Endoscopic follow-up was scheduled at 6 months after the procedure. The sites of resections were examined with white light, Narrow-Band Imaging and conventional chromoscopy with indigo carmine followed by biopsies.


      One hundred and five patients with 120 lesions were included, with a mean size of 17.5 ± 7.1 (SD) mm. Sixty-one lesions were resected underwater and 59 by CEMR. The groups were similar at baseline, regarding age, gender, average size, or histological type. Lesions in the proximal colon in the conventional group corresponded to 83% and in the UEMR group to 67.8% (p=0.073). There was no difference between groups regarding success rate (one failure in each group) and en bloc resection rate (60.6% UEMR vs 54.2% CEMR, p = 0.48). Intra-procedure bleeding was observed in five conventional resections (8.5%) and two UEMRs (3.3%) (p = 0.27). There was no perforation or delayed hemorrhage in both groups. Recurrence rate was higher in the CEMR arm (15%) than in UEMR (2%) (p=0.031). Therefore, the relative risk of 6-month recurrence rate in the CEMR group was 7.5 fold higher (95% CI - 0.98 to 58.20) with a NNT of 7.7 (95% CI - 40.33 to 4.22). The higher recurrence rate in CEMR group persisted only for lesions measuring 21—40mm (35.7 vs. 0%, p=0.04).


      This study demonstrated that UEMR was associated with lower adenoma recurrence rate than CEMR. Both endoscopic techniques are effective and have similar rates of adverse events for the treatment of non-pedunculated colorectal lesions.

      Graphical abstract

      Acronymus and abbreviations:

      CEMR (Conventional endoscopic mucosal resection), UEMR (Underwater endoscopic mucosal resection), SD (standard deviation), NNT (Number Needed to Treat), CRC (Colorectal cancer), AE (adverse events), OR (odds ratio), CI (confidence interval)
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