Misleading Mercedes-Benz sign: A case report of misdiagnosed cholecysto-hydatid cyst fistula in acute cholecystitis

Abstract

IntroductionLiver hydatid cysts represent a significant health concern globally, particularly in endemic regions like Tunisia. While they often lead to complications such as biliary fistulas, diagnostic errors can arise from radiologic signs like the “Mercedes Benz sign,” which indicates gas within the gallbladder. This report highlights the challenge of diagnosing a rare cholecysto-hydatid cyst fistula, where the presence of gas in the gallstones initially suggested a fistula. Case presentationA 30-year-old female presented with right hypochondrium pain and fever. Ultrasound suggested cholecystitis and identified two cystic formations in liver segments IVb and VII. CT scan revealed intravesicular air bubbles, suggesting a cholecysto-hydatid fistula. Emergency surgery was performed. Intraoperatively, there was an acute cholecystitis. The liver hydatid cyst of segment IVb communicated with the biliary tree and there was no cholecysto-hydatid fistula. We performed a cholecystectomy, cholangiography, and a total pericystectomy for the two liver hydatid cysts. The postoperative follow-up was uneventful. DiscussionThe “Mercedes Benz sign,” often indicating gas within gallstones, is rare but can mislead the diagnosis toward a cholecysto-hydatid cyst fistula. This case highlights the diagnostic challenge posed by this radiological feature, which led to initial suspicion of a fistula. Hydatid cysts, though common in endemic regions, can lead to diagnostic dilemmas, especially when atypical signs are present. ConclusionsThe presence of gas in the gallbladder can mislead the diagnosis, particularly when the “Mercedes Benz sign” is present, as it may suggest a rare cholecysto-hydatid cyst fistula. However, this is not always the case. Prompt and accurate evaluation, including intraoperative findings, to reinforce clinical suspicion and decision-making in endemic regions.