Describe two mechanisms that can lead to dilation of the common bile duct.

1. Common bile duct obstruction (e.g., as a result of calculi; tumors of the bile duct, pancreas, or duodenum; post-inflammatory strictures; or inflammatory change in the pancreas, such as a pancreatic pseudocyst)
2. Cholecystectomy (following cholecystectomy, the duct may measure as much as 10 mm)