The aim of this study is to compare the efficacy and safety of two standard methods of polypectomy (polyp removal), submucosal injection-assisted endoscopic mucosal resection (EMR) and full water emersion (without submucosal injection) EMR, for large colorectal polyps.

The endoscopic resection of benign colon polyps (polypectomy) plays a vital role in the prevention of colo-rectal cancer. While, small pedunculated polyps are removed with ease, large flat lesions pose a greater challenge. As a result, special techniques have been developed to assist in the removal of these difficult polyps.

During conventional colonoscopy with polypectomy, the colon lumen is insufflated with air, which flattens polyps and thins the wall of the colon. These two factors increase the risk of procedural complications such as bleeding and perforation. In order to counter these drawbacks a technique, which involves the injection of saline into the submucosal area beneath the polyp, is commonly used for the resection of large flat polyps. Theoretically, the injection creates a "safety cushion" that reduces the risks of accidental ensnarement of the muscularis propria, which can lead to iatrogenic perforation and thermal injury to the deeper tissue layers. However, the submucosal injection technique is cumbersome in patients with particularly large polyps as multiple injections are often necessary, which can blur the line between normal and abnormal tissue.

Water emersion colonoscopy is a well-established alternative to conventional "air" colonoscopy and is in fact preferred by many endoscopists. Studies have shown that using water instead of air decreases the discomfort of colonoscopy, measured by the amount of sedative and pain medication used, time to complete the colonoscopy, and recovery time, and increases cecal intubation rates. Interventional Endoscopy Services (IES) at CPMC has taken the concepts of water emersion colonoscopy one step further in order to developed a novel method of "underwater" EMR. This technique was inspired by the observation that the muscularis propria of the colon retains its native thickness (1-2 mm) and circular configuration during underwater EUS examination. Furthermore, water immersion "floats" mucosal lesions away from the deeper wall layers, eliminating the need for a "safety cushion" created by submucosal injection. One drawback to the underwater technique is that in the case of poor preps, residual feces in the colon is suspended in the water, interfering with visualization. Additionally, the use of water often causes soiling of the gurney as a result of water seepage from the rectum during the procedure, which requires additional sanitary attention during the procedure.

Inclusion Criteria:

• Patients age >18 years that are scheduled for endoscopic resection of large colo-rectal lesions who consent to this study.

Exclusion Criteria:

• Patients unable to provide informed consent.
• Patients with lesions showing adenoma invasion into the muscularis propria on EUS.
• Patients without at least one colo-rectal lesions ≥ 20mm.