Introduction: The modern-day gold standard treatment of acute cholecystitis is laparoscopic surgery. It is, however, associated with a higher risk of bile duct injury (0.1 %-1.5 %) when compared to the open approach.

Case presentation: We report a case of a patient with an acute cholecystitis in which we performed a laparoscopic cholecystectomy. We faced a destabilizing anatomy with what looked like the gallbladder and an unidentified mass, interpreted as a possible common bile duct cyst. Careful dissection allowed us to determine that what looked like a common bile duct cyst was a dilatation of "Hartmann's pouch" due to a large gallstone.

Discussion: Laparoscopic cholecystectomy reduces length of hospitalization and enhance intra-operative and postoperative morbidity compared with open cholecystectomy. It may increase the risk of bile duct injury, notably in an acute setting due to inflammation and an unclear anatomy. Hartmann's pouch with the infundibulum can sometimes unexpectedly be present beneath the common hepatic duct. In order to avoid bile duct injury, notably in an acute setting, a surgical technique was developed, the Critical View of Safety. It is a method whose sole aim is to secure identification of the cystic structures.

Conclusion: Understanding the anatomy allowed for an ultimately safe laparoscopic cholecystectomy. It is strongly advised that, in the event of atypical anatomy, a second opinion is asked of another and/or more experimented surgeon.