Endoscopic intermuscular dissection for rectum-sparing resection of a refractory rectal lesion.

Background and Aims: Endoscopic intermuscular dissection (EID) is an emerging technique that enables deeper mural resection beyond the submucosa, offering a rectum-sparing approach for fibrotic or superficially invasive rectal lesions. We describe the use of EID after multiple failed EMRs in a patient with a rectal laterally spreading tumor (LST). Methods: A 79-year-old man with a 3-cm rectal LST located 3 cm from the anal verge underwent EID after 4 previous unsuccessful resection attempts. Preprocedural evaluation with narrow-band imaging and indigo carmine chromoendoscopy suggested a fibrotic lesion with possible muscular layer involvement. The procedure was performed with the patient under general anesthesia using a therapeutic gastroscope fitted with a transparent tapered hood, and the saline-immersion technique was used to enhance layer visualization. Results: After submucosal injection and mucosal incision, a submucosal tunnel was created from the anal side. A targeted myotomy of the inner circular muscle layer exposed the longitudinal muscle, allowing intermuscular dissection. En bloc resection was achieved in 92 minutes. Histopathologic analysis confirmed a tubulovillous adenoma with high-grade dysplasia and R0 resection. The use of the saline-immersion (underwater) technique enhanced visualization of tissue planes and facilitated controlled dissection in the fibrotic area. The patient was discharged the same day without adverse events. Conclusions: EID enabled curative resection of a fibrotic rectal LST refractory to conventional EMR, and the application of the saline-immersion technique may represent a novel technical modification that improves visualization and safety in challenging fibrotic cases.