Endoscopic intermuscular dissection of a rectal gastrointestinal stromal tumor.

Background and Aims: Rectal gastrointestinal stromal tumors (GISTs) are rare, and optimal management of localized disease remains uncertain. Endoscopic intermuscular dissection (EID) is an emerging minimally invasive technique that allows en bloc removal of selected subepithelial lesions that do not extend beyond the circular layer of the muscularis propria while preserving anorectal anatomy. We present a case of a rectal GIST successfully treated with EID. A 53-year-old man undergoing high-risk colorectal cancer surveillance was found to have a subepithelial rectal lesion 1.5 cm proximal to the dentate line. Endoscopic ultrasound and biopsy confirmed a low-grade GIST. The patient was referred for endoscopic submucosal dissection. Methods: The procedure began with thermal marking followed by repeated methylene blue injections to maintain a well-defined submucosal plane. Once the lesion was identified as originating from the muscularis propria, the approach was converted to EID, allowing capsule-preserving en bloc resection within the intermuscular space. The defect was subsequently closed with a running endoscopic suturing device. Results: Pathology confirmed a spindle-cell, low-grade GIST with negative margins and no lymphovascular invasion. At 14-month follow-up, there were no delayed adverse events or evidence of recurrence. Conclusions: This case demonstrates the feasibility and safety of EID for small rectal GISTs originating from the muscularis propria.