Original article Clinical endoscopy| Volume 91, ISSUE 3, P643-654.e2, March 2020

Underwater versus conventional endoscopic resection of nondiminutive nonpedunculated colorectal lesions: a prospective randomized controlled trial (with video)

  • Andrew W. Yen
    Reprint requests: Andrew W. Yen, MD, MAS, FACG, FASGE, Sacramento Veterans Affairs Medical Center, VANCHCS, Division of Gastroenterology, 111/G, 10535 Hospital Way, Mather, CA 95655.
    Sacramento Veterans Affairs Medical Center, VA Northern California Health Care System, Division of Gastroenterology, Mather, California, USA

    University of California Davis School of Medicine, Sacramento, California, USA
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  • Joseph W. Leung
    Sacramento Veterans Affairs Medical Center, VA Northern California Health Care System, Division of Gastroenterology, Mather, California, USA

    University of California Davis School of Medicine, Sacramento, California, USA
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  • Machelle D. Wilson
    Clinical and Translational Science Center, Department of Public Health Sciences, Division of Biostatistics, University of California Davis, Sacramento, California, USA
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  • Felix W. Leung
    Sepulveda Ambulatory Care Center, VA Greater Los Angeles Healthcare System, Division of Gastroenterology, North Hills, California, USA

    David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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Published:October 16, 2019DOI:

      Background and Aims

      Incomplete resection of colorectal neoplasia decreases the efficacy of colonoscopy. Conventional resection (CR) of polyps, performed in a gas-distended colon, is the current standard, but incomplete resection rates of approximately 2% to 30% for nondiminutive (>5 mm), nonpedunculated lesions are reported. Underwater resection (UR) is a novel technique. The aim of this study was to determine the incomplete resection rates of colorectal lesions removed by UR versus CR.


      In a randomized controlled trial, patients with small (6-9 mm) and large (≥10 mm) nonpedunculated lesions were assigned to CR (gas-distended lumen) or UR (water-filled, gas-excluded lumen). Small lesions in both arms were removed with a dedicated cold snare. For CR, large lesions were removed with a hot snare after submucosal injection. For UR, large lesions were removed with a hot snare without submucosal injection. Four-quadrant biopsy samples around the resection sites were used to evaluate for incomplete resection.


      Four hundred sixty-two eligible polyps (248 UR vs 214 CR) from 255 patients were removed. Incomplete resection rates for UR and CR were low and did not differ (2% vs 1.9%, P = .91). UR was performed significantly faster for lesions ≥10 mm in size (10-19 mm, 2.9 minutes vs 5.6 minutes, P < .0001); ≥20 mm, 7.3 minutes vs 9.5 minutes, P = .015).


      Low incomplete resection rates are achievable with UR and CR. UR is effective and safe with the advantage of faster resection and potential cost savings for removal of larger (≥10 mm) lesions by avoiding submucosal injection. As an added approach, UR has potential to improve the cost-effectiveness of colonoscopy by increasing efficiency and reducing cost while maintaining quality. (Clinical trial registration number: NCT02889679.)

      Graphical abstract


      CR (conventional resection), UR (underwater resection), VANCHCS (Veterans Affairs Northern California Health Care System)
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