Short- and Long-Term Outcomes of Underwater Versus Conventional Colorectal Endoscopic Submucosal Dissection: A Large Retrospective Real-World Cohort Study

BACKGROUND: Underwater techniques are increasingly used in colorectal endoscopic submucosal dissection (ESD), but real-world data remain limited. We compared underwater and conventional colorectal ESD. METHODS: This retrospective observational study included consecutive colorectal ESD lesions at a tertiary referral center between May 2010 and September 2024. The analysis used propensity score overlap weighting. Procedural outcomes included dissection speed, procedure time, resection outcomes, and adverse events. Intraoperative perforation and long-term outcomes were assessed descriptively. RESULTS: Among 1,649 lesions, 1,635 were included in the main analysis (conventional, 914; underwater, 721). Dissection speed was higher in the underwater group (speed ratio, 1.23; 95% CI, 1.14-1.32; p<0.001), whereas procedure time was similar. Failure to complete ESD was less frequent in the underwater group, with no clear differences in en bloc resection, R0 resection, or adverse events. Among 56 intraoperative perforation cases, all perforation sites were closed endoscopically, no emergent surgery was required, and short-term clinical outcomes showed no clear differences. Median survival follow-up was 3.09 [IQR, 0.48-7.39] and 2.10 [IQR, 0.56-3.72] years in the conventional and underwater groups, respectively; overall death occurred in 27/824 (3.3%) and 3/622 (0.5%) patients, with no colorectal cancer-related deaths. CONCLUSIONS: The underwater technique was associated with higher dissection speed, although this did not translate into a shorter procedure time or clear improvements in other procedural outcomes. These findings suggest a potential technical advantage during dissection, while its clinical relevance remains to be established.