Prospective randomized trial comparing conventional and underwater endoscopic submucosal dissection for superficial colorectal neoplasms.

Background and study aims: This study compared procedure-related outcomes of conventional and underwater endoscopic submucosal dissection (ESD) for superficial colorectal neoplasms (SCNs). Patients and methods: In this single-center, randomized controlled trial, patients with SCNs meeting the indications of the Japanese guidelines for ESD were randomly assigned to undergo conventional ESD (CESD) or underwater ESD (UESD) performed by an expert. The primary endpoint was dissection speed, defined as the specimen area per ESD time. Results: We analyzed the data of 69 and 70 CESD and UESD cases, respectively; however, no significant differences were found in median dissection speed (17.4 and 19.9 mm2/min, respectively; P=0.19). Multiple regression analysis revealed that the suitable positional relationship between the lesion and the direction of gravity (nongravity side for CESD and gravity side for UESD) was independently and positively associated with dissection speed (P<0.001). En bloc resection was achieved without perforation in all cases. The incidence of post-ESD coagulation syndrome was not significantly different between the two groups (4.3% vs. 2.9%, respectively; P=0.68). Conclusions: UESD did not expedite dissection speed in the overall patient population. CESD and UESD may be complementary in the colorectum depending on the positional relationship between the lesion and the direction of gravity.