Colorectal endoscopic submucosal dissection (ESD) enables en bloc resection of large superficial colorectal neoplasia but remains technically demanding and may be limited by suboptimal visualization, intraprocedural bleeding, smoke accumulation, and prolonged procedural time. Underwater ESD (UESD), performed under saline immersion rather than gas insufflation, has been proposed as a strategy to improve the operative field and facilitate submucosal dissection.

This prospective, multicenter, open-label, randomized controlled trial was designed to compare UESD with conventional gas-assisted ESD (GESD) for colorectal neoplasia referred for ESD across Italian tertiary centers. The primary objective was to assess non-inferiority of UESD versus GESD in terms of en bloc resection. Secondary objectives included comparison of histological resection quality, procedural efficiency, intraprocedural events, procedural field visualization, and post-procedural adverse events.

Colorectal ESD is an established organ-preserving technique for the en bloc resection of superficial colorectal neoplasia, particularly when conventional endoscopic mucosal resection is unlikely to achieve complete single-piece excision. However, colorectal ESD is technically demanding because of the thin colonic wall, unstable scope position, narrow submucosal space, intraprocedural bleeding, smoke generation, and difficulty in maintaining a stable dissection plane.

Underwater ESD has emerged as a modified operative environment in which luminal insufflation is discontinued and the target segment is immersed in saline. Saline immersion may improve visualization of the submucosal layer and of submucosal vessels, limit smoke persistence in the operative field, and facilitate more stable dissection. Although initial retrospective and comparative experiences have suggested procedural advantages of underwater ESD, high-quality randomized comparative data remain limited, particularly in Western multicenter practice.

This study was therefore designed as a prospective multicenter randomized trial across Italian tertiary referral centers to compare underwater ESD with conventional gas-assisted ESD for colorectal neoplasia referred for ESD. Patients were allocated 1:1 to either UESD or GESD. The primary endpoint was en bloc resection. Secondary endpoints included R0 resection, procedural time, dissection speed, intraprocedural bleeding, need for hemostatic forceps, smoke interference, vessel visualization, cutting-plane visualization, post-procedural pain, post-ESD coagulation syndrome, perforation, and delayed bleeding. The technical conduct of ESD apart from the assigned luminal environment was left to expert operator discretion in order to preserve real-world tertiary-center practice.

Inclusion Criteria:

Adults aged 19 years or older

Colorectal neoplastic lesion referred for endoscopic submucosal dissection

Lesion considered amenable to en bloc endoscopic resection by ESD according to expert pre-procedural endoscopic assessment

Written informed consent provided

Exclusion Criteria:

Known or suspected deep invasive neoplasia

Inflammatory bowel disease

Uninterrupted antithrombotic therapy

Known coagulopathy

Any clinical or lesion-related condition considered unsuitable for colorectal ESD by the treating endoscopist

Anonymsed data upon written and motivated requests

after the publication, for 5 years at least