[Image of the month].

A 76-year-old woman complained of abdominal pain in the right upper quadrant and fever that had been developing over the previous 10 days. On examination, she presented pain in the right upper quadrant with positive Murphy’s sign. Computed tomography showed the presence of acute cholecystitis and, as a casual finding, the presence of cholelithiasis with air in its interior (Fig. 1). The presence of gas in the interior of the calculus or Mercedes-Benz sign is due to the development of fissures in the process of crystallization; approximately half of calculi present fissures, but only some contain gas in their interior.