Introduction <p>Cholecystoduodenal fistula is a rare complication of chronic cholecystitis. When associated with gallbladder wall thickening, it can closely mimic gallbladder carcinoma both clinically and radiologically, creating significant diagnostic and therapeutic challenges.</p> Case Presentation <p>We report the case of a 50-year-old female who presented with abdominal pain and fever. Imaging revealed gallbladder wall thickening with intramural nodules and features suspicious for carcinoma with a malignant cholecystoduodenal fistula. Based on this working diagnosis, the patient underwent open radical cholecystectomy with segmental resection of the pyloroduodenal channel, sleeve resection of the transverse colon, and reconstruction with a retrogastric–retrocolic posterior isoperistaltic loop. Histopathological examination of the resected specimen, however, demonstrated xanthogranulomatous cholecystitis (XGC) with fistulous extension, without evidence of malignancy.</p> Conclusion <p>This case underscores the difficulty in distinguishing XGC with fistula from gallbladder carcinoma, even with advanced imaging. It highlights the importance of considering XGC in the differential diagnosis of gallbladder masses with fistulous communication, as definitive diagnosis rests on histopathology and has significant implications for surgical management.</p>