Cholecysto-biliary fistula mimicking type 1 Mirizzi syndrome: A case report.

Background: Mirizzi syndrome is a rare complication of chronic gallstone disease in which an impacted stone causes compression or erosion of the common hepatic duct. Accurate preoperative diagnosis is crucial but often challenging. We report a case that was preoperatively diagnosed as type 1 Mirizzi syndrome but was found intraoperatively to be type 4, involving a cholecysto-biliary fistula and complete erosion of the common hepatic duct.

Case summary: A 74-year-old woman presented with right upper quadrant discomfort. Initial workup including ultrasound and magnetic resonance cholangiopancreatography suggested Mirizzi syndrome type 1 due to extrinsic compression of the common hepatic duct. Endoscopic retrograde cholangiopancreatography confirmed a large stone without evidence of fistula. The patient underwent robotic-assisted cholecystectomy, during which a 4 cm stone was found eroding into the common hepatic duct, consistent with type 4 Mirizzi syndrome. Intraoperative cholangioscopy confirmed the fistula and allowed primary repair. The patient recovered uneventfully and was discharged on postoperative day one.

Conclusion: Preoperative imaging may fail to identify fistula formation in Mirizzi syndrome. Intraoperative assessment remains critical for accurate diagnosis and safe surgical management.