There is no reliable endoscopic method to selectively resect deeper layers of the gut wall or to access the peritoneal cavity and prevent peritoneal soiling.

To determine the technical feasibility and safety of submucosal endoscopy with mucosal flap (SEMF) in accessing the peritoneal cavity through a large full-thickness gastric-muscle–wall resection.

Ex vivo feasibility exploration and survival animal study.

Ex vivo samples were obtained from fresh harvested organs. In vivo procedures were conducted with the pigs under standard general anesthesia.

High-pressure carbon dioxide (CO₂) injection and balloon dissection created a large submucosal working space for insertion of a cap-fitted endoscope. By using the EMR cap, a full-thickness resection of the muscularis propria was performed. This full-thickness defect was sealed with the overlying mucosal flap and the use of hemoclips or tissue anchors.

By using the SEMF technique in the ex vivo experiment, the gastric wall was successfully traversed in each stomach after submucosal dissection and full-thickness resection of the musclaris. Similarly, by using the SEMF technique in the in vivo procedures, the peritoneal cavity was successfully accessed and the defect was completely sealed by using the mucosal flap. All animals survived 1 week after the procedure. Ulceration was noted in 3 pigs, and a small bowel injury was noted in 1 pig. Leak testing was negative in all stomachs.

By using the SEMF technique, submucosal space endoscopy and deep-layer gastric-wall resection were successfully performed. Furthermore, the mucosa overlying the dissected submucosal space served as a safe flap valve, preventing peritoneal leakage.