Clinical Outcomes of Partial Injection Underwater Endoscopic Mucosal Resection for Superficial Non-ampullary Duodenal Epithelial Tumors (With Video).

Objectives: Although endoscopic resection is widely performed for superficial non-ampullary duodenal epithelial tumors (SNADETs), conventional endoscopic mucosal resection (CEMR) may be associated with suboptimal complete resection rates. Partial injection underwater EMR (PI-UEMR) has been proposed to improve the visualization of distal lesion margins and facilitate en bloc resection. We aimed to evaluate the outcomes of PI-UEMR for SNADETs, using CEMR as a historical institutional comparator. Methods: This single-center observational cohort study included patients who underwent endoscopic mucosal resection for SNADETs between September 2015 and December 2025. Lesions treated with CEMR or PI-UEMR were analyzed. The primary outcomes were en bloc and R0 resection rates. The secondary outcomes included histological diagnosis and procedure-related adverse events, including intraoperative perforation, delayed perforation, and delayed bleeding. Results: In total, 77 lesions in 73 patients were analyzed, including 39 treated with CEMR and 38 treated with PI-UEMR. The en bloc resection rates were 90.0% and 97.4% in the CEMR and PI-UEMR groups, respectively. The R0 resection rate was significantly higher in the PI-UEMR group than in the CEMR group (89.4% vs. 69.2%). Histological diagnoses were similar between the groups. No intraoperative perforation occurred in either group. No procedure-related adverse events, including delayed perforation or bleeding, were observed in the PI-UEMR group. Conclusions: While maintaining a favorable safety profile, PI-UEMR was associated with a higher R0 resection rate than CEMR in this study. It may represent an effective endoscopic treatment option for SNADETs, particularly when precise visualization of the distal lesion margins is required.