Volume 3, Issue 12, Pages 375-377 (December 2018) Underwater endoscopic submucosal dissection in saline solution using a bent-type knife for duodenal tumor  Mitsuru Nagata, MD  VideoGIE  Volume 3, Issue 12, Pages 375-377 (December 2018) DOI: 10.1016/j.vgie.2018.09.015 Copyright © 2018 American Society for Gastrointestinal Endoscopy Terms and Conditions

Figure 1 Hook Knife J is a monopolar knife with a bent and rotatable tip along with a water jet function. VideoGIE 2018 3, 375-377DOI: (10.1016/j.vgie.2018.09.015) Copyright © 2018 American Society for Gastrointestinal Endoscopy Terms and Conditions

Figure 2 Explanation of “elongation of reach” in underwater condition. A, “Elongation of reach” due to the underwater condition. During use of the GIF-Q260J endoscope (Olympus, Tokyo, Japan), an object in air at a 3-mm distance from the endoscope will appear the same on screen as an underwater object at a 5.7-mm distance from the endoscope because of the zoom effect. B, When the knife is moved with the same sense of distance on the screen and same angle of the endoscope, the moving distance of the knife tip can appear larger in underwater conditions than in air because the arc length is represented by “r (or R) × θ” (r or R, radius; θ, central angle) in the circular measure. VideoGIE 2018 3, 375-377DOI: (10.1016/j.vgie.2018.09.015) Copyright © 2018 American Society for Gastrointestinal Endoscopy Terms and Conditions

Figure 3 Underwater endoscopic submucosal dissection for duodenal tumor. A, The lesion (25 mm in diameter) was located at the superior duodenal angle. B, The lesion was located at the gravitational lower side with the patient in the left lateral decubitus and supine positions. Therefore, water collected around the lesion, and the interface between the air and water obstructed the visual field. C, Owing to severe fibrosis and halation, the boundary between the submucosal and muscle layers was unclear. D, The underwater condition enabled recognition of the boundary between the submucosal and muscle layers. E, Buoyancy aided the opening of the mucosal flap against gravity, making the approach to the submucosal layer easier. F, En bloc resection was achieved without any adverse events. Complete resection was histopathologically proven. VideoGIE 2018 3, 375-377DOI: (10.1016/j.vgie.2018.09.015) Copyright © 2018 American Society for Gastrointestinal Endoscopy Terms and Conditions