Supplementary Material for: Utility of under-gel endoscopic mucosal resection with partial submucosal injection and under-gel precutting endoscopic mucosal resection for difficult colorectal polyp cases

Background: Here, we evaluated the utility of under-gel endoscopic mucosal resection (EMR) with partial submucosal injection (PI) and under-gel precutting EMR for difficult-to-treat colorectal polyps. Methods: A retrospective case series was conducted from April 1st, 2020 to April 1st, 2021 at St. Luke's International Hospital (Japan). We included all consecutive patients who underwent colonoscopy and subsequent under-gel EMR with PI and under-gel precutting EMR. Baseline and clinical data were obtained from electronic medical records. Results: Under-gel EMR with PI was performed in six patients, treating a total of seven lesions. In this group, 50% (3/6) were women (mean age = 59.2 years). The mean procedure time and specimen size was 5.1 min and 12.1 mm, respectively, achieving a 100% (7/7) en bloc resection rate. Under-gel precutting EMR was performed in eight patients. In this group, 50% (4/8) were women (mean age = 66.1 years). The mean procedure time and specimen size was 22.6 min and 23.0 mm, respectively; en bloc resection rate was 62.5% (5/8). Regarding lesions over 20 mm in diameter, the en bloc resection rate was 50% (3/6). No complications were observed. Conclusions: PI is potentially useful for colorectal polyps where the distal end is not visible; when PI cannot be used, pre-cutting EMR may constitute another troubleshooting method for difficult-to-treat colorectal polyps. The gel immersion method is also a viable option when the use of water causes rapid mixing of blood and residual stool, resulting in poor visibility.