Incidental finding of uncomplicated cholelithiasis with several large, rim-enhancing multifaceted gallstones. One stone reveals the classic “Mercedes-Benz” sign, seen as a triradiate pattern of central gas-containing fissures as described.

Around 50% of gallstones contain some amount of fissuring, but few contain gas and are less commonly visible on imaging. Rim calcification is more common in pigment gallstones due to higher biliary calcium concentrations, and is thought to be a result of chronic common bile duct obstruction and low-grade gallbladder wall inflammation.

The three types of gallstones include: 1) cholesterol (10%), 2) pigment (10%), and 3) mixed (80%).  Cholesterol stones contain >50% cholesterol and form with supersaturation of bile. Pigment stones are comprised of mostly bile and contain less than 20% cholesterol. If rim calcifications are seen, they are usually pigment stones.