Cholecystogastric fistula masquerading as gastrointestinal stromal tumour

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Abstract
Rationale: We present the case of gallbladder adenomyomatosis (GA)-induced cholecystogastric fistula (CGF) that mimicked an invasive gastric gastrointestinal stromal tumor (GIST), leading to diagnostic and surgical challenges in an emergency setting. Patient concerns: A 71-year-old woman presented to the emergency department with acute abdominal pain and clinical signs of mechanical small-bowel obstruction (SBO). Diagnoses: Contrast-enhanced abdominal computed tomography (CT) revealed a 6-cm mass along the gastric antrum with apparent hepatic invasion and concurrent features of SBO. The gallbladder was not visualized. Esophagogastroduodenoscopy (EGD) demonstrated a subepithelial tumor-like bulge with a small mucosal opening in the gastric antrum, raising suspicion of a fistulous tract. Interventions: Emergency exploratory laparotomy identified two phytobezoars in the small bowel, which were treated by segmental resection and primary anastomosis. The gastric mass was found to be densely adherent to the liver, and bile leakage was encountered during dissection, prompting intraoperative hepatobiliary consultation. Outcomes: Histopathological examination of the resected specimen confirmed GA with inflammatory granulation tissue at the gallbladder–gastric serosal interface, with no evidence of malignancy. The patient recovered uneventfully and was discharged 29 days postoperatively. Lessons: This case highlights a novel and clinically significant diagnostic pitfall: GA-induced CGF can convincingly simulate an invasive gastric neoplasm on multimodal imaging and endoscopy. Recognition of biliary red flags, including non-visualization of the gallbladder on CT, a mucosal opening adjacent to a subepithelial-appearing lesion on EGD, and intramural cystic foci on imaging, is essential for accurate preoperative diagnosis.

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