Underwater endoscopic submucosal dissection in the gastrointestinal tract: technical review and dual-approach endoscopic submucosal dissection.

Endoscopic submucosal dissection (ESD) has become an established technique for en bloc resection of superficial gastrointestinal neoplasms. However, conventional ESD (CESD) under gas insufflation remains technically demanding, particularly in gravity-side lesions or in cases with submucosal fibrosis. Underwater ESD (UESD) was developed to overcome these challenges. Complete submergence mitigates gravity-related difficulties, enhances visualization through the natural zoom effect, and facilitates submucosal dissection via buoyancy and water pressure. Retrospective data further suggest that UESD may reduce the risk of post-ESD coagulation syndrome, which is likely attributable to the heat sink effect. UESD can also be integrated with device-assisted traction and pocket creation methods. However, limitations, such as visual field impairment caused by bleeding or bubble formation, remain concerns, and their optimal management requires further investigation. Nevertheless, UESD allows procedural flexibility by switching between UESD and CESD within the same procedure, herein referred to as dual-approach ESD. Despite its routine use in clinical practice, dual-approach ESD has not been clearly distinguished from UESD in most clinical studies, complicating comparisons with CESD. To advance both clinical practice and research, future investigations should clearly differentiate UESD from dual-approach ESD for a more accurate evaluation. Furthermore, appropriate procedural selection requires careful consideration of multiple factors.