It's typically attributed to some form of blockage of the common bile duct due to stones. However, in some cases, such as after the gallbladder is removed, enlargement can occur but there is no explanation for why the enlargement is found.
i have a enlarge bile duct and it is 12mm and i can't eat very much. i fell sick
If they know that your CBD is 12mm what tests have you had? Stones, strictures, tumors, and sphincter of Oddi dusfunction would all be possibilities. Further evaluation would certainly be warranted.