Planar-Type Gastrointestinal Stromal Tumor in the Sigmoid Colon Presenting as Perforation and Peritonitis

Abstract

Abstract Introduction/Objective Gastrointestinal Stromal Tumor (GIST) is the most common mesenchymal neoplasm of the stomach, and it also can involve the small bowel, rectum, and esophagus. It can be incidentally found on imaging or can present with nonspecific GI symptoms and/or bleeding. Non-rectal colonic GISTs are extremely rare. A few cases of small bowel/colonic GISTs presenting as a non-discrete mass and forming a diverticulum with/without perforation have been documented in the literature and referred to as interstitial cells of Cajal hyperplasia/planar-type GIST. We report another case of non-rectal colonic planar-type GIST presenting as a diverticular perforation and peritonitis and the frequency of such presentation at our institution. Methods/Case Report A 43-year-old female presented with fever and abdominal pain. CT scan showed pneumoperitoneum and the patient was taken for surgery which revealed a sigmoid colon perforation. Gross examination of the sigmoidectomy specimen revealed a perforated diverticulum (2.5 cm). Sectioning of the diverticular pouch did not reveal a grossly obvious mass. Histologic examination revealed a band-like proliferation of bland spindle cells along the entire length of the diverticulum partially replacing the muscularis propria. No mitoses were identified. On immunohistochemistry, the cells were diffusely positive for DOG-1, CD34, and negative for MNF116, S100, and desmin; thus, a diagnosis of a planar-type GIST was made. In our institution, a total of 143 GISTs were resected between Jan 2000 and May 2022. The most common site was the stomach (73%), and the most common presentation was anemia and/or GI bleeding (27%). The index case is the only non-rectal colonic GIST (0.7%) in our cohort that also presented with perforation (0.7%). Results (if a Case Study enter NA) NA. Conclusion Non-rectal colonic GISTs are extremely rare (0.7% in our cohort) and may not present as a grossly apparent mass. Therefore, pathologists should be cognizant of planar-type GIST while evaluating colonic diverticular perforations.