Appendiceal polyps are challenging to resect endoscopically, and many deep lesions are traditionally referred to for surgery. The currently available endoscopic alternative, endoscopic full-thickness resection (eFTR), carries a relatively high risk of appendicitis and residual lesion. Underwater endoscopic mucosal resection (uEMR) enables larger en bloc resections compared with conventional EMR by exploiting the buoyancy effect. In the underwater environment, buoyancy facilitates invagination of the appendiceal mucosa into the caecal lumen, providing safe access to polyps extending into or involve the appendiceal orifice. In combination with cap assistance and suction, uEMR allows controlled removal of lesions in this anatomically challenging region, potentially avoiding unnecessary surgery. Sahlgrenska University Hospital/Östra is the tertiary referral center for advanced colorectal polypectomy in Western Sweden.To evaluate whether uEMR is a safe and effective method for removing colorectal polyps involving the appendiceal orifice, and to describe procedural outcomes and technical insights.

Since 2019, all advanced polypectomy procedures at our center have been prospectively registered in a dedicated database. uEMR was introduced in January 2023, with its use for appendiceal-orifice lesions initiated in June 2023. We conducted a retrospective review of all uEMR procedures involving the appendiceal orifice performed between June 2023 and December 2024.

Twenty uEMR procedures involving the appendiceal orifice were identified. The mean patient age was 63 years (range 28–86), and 55% were women. The median polyp size was 16.1 mm (IQR 10–30 mm). Based on recommended classifications, 25% of lesions reached the appendiceal orifice with identifiable borders, whereas 75% completely covered the orifice and borders were not identifiable prior to uEMR. In 45% of cases, 25–50% of the orifice was involved, and in 55% >50% was covered. Lesions were classified as Paris 0-IIa (80%) or 0-Is (20%), and JNET 1 (60%), JNET 2a (35%) or JNET 2b (5%).

Intraoperative bleeding occurred in one case and was successfully managed endoscopically. No intraoperative perforations, delayed perforations, or delayed bleedings were observed. One patient developed appendicitis the day after the procedure; imaging revealed inguinal hernia-related entrapment of the appendix, and the patient recovered with conservative management and intravenous antibiotics.

Technical success was achieved in 90% of cases, while two patients were referred for surgery due to incomplete or unsuccessful resection. En block resection was achieved in 84.2% of cases, and R0 resection in 63.2%. The most common histology was sessile serrated lesion (SSL, n=11), followed by tubular adenoma (n=4), tubulovillous adenoma (n=2), hyperplastic polyp (n=1), and inflammatory polyp (n=1). Dysplasia was identified in one SSL, and high-grade dysplasia was found in one tubular adenoma and one tubulovillous adenoma. Seven patients underwent follow-up endoscopy within 12 months, with no recurrences detected. 

uEMR is a safe and effective technique for resection of colorectal polyps involving the appendiceal orifice in a tertiary high-volume setting. High en bloc and R0 resection rates were achieved, with minimal adverse events and no local recurrence. These findings support uEMR as a preferred minimally invasive approach for selected lesions in this anatomically challenging location.