A Case of Intracholecystic Papillary Neoplasm Extending Through a Cholecysto-Colonic Fistula.

We report the case of a 76-year-old man who presented with pain in the right upper abdomen. Laboratory and radiological examinations revealed cholangitis, cholelithiasis, and a gallbladder tumor adhering to the transverse colon. After receiving conservative therapy for cholangitis, the patient underwent surgery for the gallbladder disease. On surgery, a cholecysto-colonic fistula communicating the gallbladder and transverse colon was revealed, and combined resection of the gallbladder and partial transverse colon was performed. The resected sample revealed an intracholecystic papillary neoplasm with a focal invasive component, xanthogranulomatous cholecystitis in the gallbladder, and a cholecysto-colonic fistula. Xanthogranulomatous cholecystitis caused fibrous adhesion and penetration from the gallbladder and transverse colon, resulting in the fistula. A noninvasive component of the intracholecystic papillary neoplasm horizontally extended into the transverse colon across the fistula, whereas a small invasive component on the hepatic side was observed. As the intracholecystic papillary neoplasm did not "invade" the transverse colon, we concluded that the pathological T-stage of the intracholecystic papillary neoplasm was pT1b (invading the muscularis propria of the gallbladder). This was a case where a large gap between preoperative diagnosis (cT3) and pathological diagnosis (pT1b) occurred and a careful explanation of the atypical state and cause of the discrepancy in diagnosis was required.