Background and Aim Underwater endoscopic mucosal resection (U‐EMR) has been attracting much attention as treatment for patients with nonampullary duodenal epithelial tumors (NADETs). We aim to compare treatment outcomes, including submucosal resectability, between patients undergoing U‐EMR and conventional endoscopic mucosal resection (C‐EMR) for NADET. Methods We conducted a retrospective review of 38 patients with NADET treated by U‐EMR or C‐EMR. In the resected specimens, we measured the horizontal length, the vertical distance from the muscularis mucosa to the margin at the deepest site, and the overall submucosal area. The submucosal index (SMI) was defined as the overall submucosal area divided by the largest horizontal length. These values and other treatment outcomes were compared between NADETs resected by U‐EMR and C‐EMR. Results The median size of lesions was 7 mm with a range of 3–13 mm. Although the incidence of adverse events and the rates of en bloc and R0 resection were not different in the two groups, the median procedure time was significantly shorter in the U‐EMR group (11 min vs 13 min; P = 0.045). The median submucosal depth at the deepest site (1.22 mm vs 1.08 mm; P = 0.38) and the median SMI (0.44 vs 0.41; P = 0.42) were not different between groups. Conclusions The resectability between NADETs treated by U‐EMR and C‐EMR was comparable. These results, together with the shorter procedure time required for U‐EMR, suggest that U‐EMR may have the potential to be the first choice for small to medium‐sized NADET.

A 14‐year‐old girl, who had been diagnosed with blue rubber bleb nevus syndrome, was referred to our hospital because of iron deficiency anemia. Esophagogastroduodenoscopy revealed a dark and red‐colored vascular malformation occurring just above the duodenal papilla. Because the lesion was regarded as the cause of the anemia, we performed polidocanol injection therapy with bile duct stenting. Since esophagogastroduodenoscopy performed a month later revealed a scarred ulcer, the bile duct stent was removed. She has been under observation as an outpatient without any symptoms.