Biliary tract lithiasis most often begins with a calculus (stone) forming within the gallbladder. A small enough calculus (or part of a calculus) may become impacted in the neck of the gallbladder or cystic duct, producing acute cholecystitis. The stone may travel further down into the common bile duct, and impaction in this duct (choledocholithiasis) may produce obstruction with jaundice. The stone may travel further down and, near the ampulla, obstruct the pancreatic duct, leading to acute pancreatitis. The stone may pass through the ampulla and out into the duodenum.

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