Gastrointestinal stromal tumor (GIST) usually arises in the stomach, whereas primary omental GIST is extremely rare. We report a case of a 43-year-old man with chronic hepatitis B and diabetes mellitus who was referred for evaluation of an upper abdominal mass detected during regular surveillance ultrasonography. Computed tomography and magnetic resonance imaging revealed an approximately 8-cm hypervascular mass between the liver and gastric antrum, initially suggesting an exophytic gastric GIST. However, esophagogastroduodenoscopy showed no definite gastric subepithelial or intraluminal lesion. Ultrasound-guided core needle biopsy suggested GIST with positivity for C-kit, CD34, and DOG1. The patient underwent tumor excision with gastric wedge resection. Final pathology demonstrated a mixed epithelioid and spindle cell GIST arising from the omentum, with secondary involvement of the stomach and falciform ligament. Although the tumor was categorized as moderate risk on final pathologic assessment, adjuvant imatinib therapy was initiated after multidisciplinary discussion because of clinically unfavorable features, including extragastrointestinal omental origin, large size, necrosis, and increased proliferative activity. The patient remains well without recurrence. This case emphasizes the diagnostic difficulty in determining the primary site of upper abdominal mesenchymal tumors and the importance of final surgical pathology for risk assessment and treatment planning.
Kim et al. (Sun,) studied this question.