Post written by Mitsuru Nagata, MD, from the Department of Endoscopy, Shonan Fujisawa Tokushukai Hospital, Kanagawa, Japan.

The present study aimed to investigate the usefulness and safety of underwater endoscopic submucosal dissection (UESD) in saline solution using a monopolar knife for colorectal tumors. This study is unique because a monopolar knife was used for UESD for the first time.

Only few cases of UESD have been reported to date. Previous studies on UESD involved the use of only a bipolar knife in saline solution. Although bipolar knives for ESD are marketed, they do not constitute commonly used surgical devices. I felt it was necessary to investigate the efficiency of UESD using a monopolar knife.

The results of this study showed that UESD in saline solution with a monopolar knife is safe and efficient for the treatment of colorectal tumors. Although saline solution has high electrical conductivity, a monopolar knife can be used in the same setting as an electrosurgical generator used in conventional ESD (CESD) if the tip of the knife has high current density. The benefits of UESD are good visualization (natural zoom effect and disappearance of halation), buoyancy, and heat-sink effect. The water pressure created by the water jet function of the endoscope aids in the opening of the cutting edge of the mucosa, thereby easing the approach to the submucosal layer. The visual field loss due to splashing water is avoided because the pressure is applied from the underwater.

UESD or CESD must be performed in appropriate situations such as when one of them is advantageous over the other. Some cases in which UESD can be more advantageous than CESD are as follows: (1) presence of severe fibrosis in the submucosa, (2) difficulty in performing CESD because the lesion is located against gravity, and (3) obstruction of the visual field by the fat tissue in the submucosa.

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