Underwater Endoscopic Mucosal Resection of a Large Flat Adenoma with Pseudoinvasion in the Rectum

optimal in pseudodepressed lesions. Air insufflation was switched off, luminal air was aspirated, water was instilled using the water jet until complete immersion of the lumen was achieved ( Fig. 2 a), and the lesion was resected in piecemeal fashion using a conventional 25-mm oval snare (CJ-ADR-23–230–025; Nova LightSystems, Life Partners Europe, Bagnolet, France) and usual electrosurgical settings (Endocut effect 2, ICC 200; ERBE Elektromedizin, Tübingen, Germany) ( Fig. 2 b, c). A bleeding vessel was identified during the procedure ( Fig. 3 a) and managed with a hemostatic clip ( Fig. 3 b). Histological analysis revealed a tubulovillous adenoma with high-grade dysplasia and rare adenomatous glands within the submucosa extending from the overlying epithelium, with no associated desmoplastic reaction, corresponding to an adenoma with misplaced epithelium ( Fig. 1 c). A follow-up procedure performed 3 months later revealed no residual lesion. Water immersion preserves the circular configuration of the muscularis propria of the colon while folds of mucosa and submucosa project into the lumen away from the muscle layer, avoiding the need for submucosal injection used in conventional EMR [1, 2] . Bleeding during UEMR is uncommon, and the point of origin is clearly identified underwater [1] . Adenoma with misplaced epithelium is a rare entity formerly known as pseudoinvasive adenoma, which corresponds to an extension of the adenomatous glands of an adenoma into the submucosa through minor defects of the muscularis mucosae [3, 4] . The distinction of this entity from an invasive cancer in which neoplastic epithelium, such as desmoplasia, frank atypia, or pleomorphism, is present in the submucosa may be difficult but is crucial as the management and prognosis of an adenoma with misplaced epithelium is identical to an adenomatous polyp [3, 4] . Keywords