A giant gastrointestinal stromal tumour mimicking gastric diverticulum: a case report

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract, arising from the interstitial cells of Cajal. Although typically located in the stomach, they may present atypically, mimicking benign lesions such as gastric diverticula. This is a case of a 40-year-old Nepali female with rheumatoid arthritis and diabetes mellitus presenting with postprandial vomiting, abdominal fullness, and significant weight loss, where radiologic evaluation suggested a large posterior gastric diverticulum. On surgical excision, a gastric diverticulum was isolated, and histopathological analysis confirmed the diagnosis of a gastric GIST (C-kit+, DOG-1+, and CD34+). Despite low mitotic activity, the tumor was classified as high risk due to its size (>10 cm), and the patient was commenced on adjuvant imatinib therapy. This case highlights a gastric GIST masquerading as a giant gastric diverticulum and emphasizes the importance of considering GIST as a differential diagnosis of large gastric masses.