The differential diagnosis presented above is correct and comprehensive. Given your age and lack of other significant co-morbidities, the most probable cause would be a stone/calculus in the common bile duct (choledocholithiasis). If the MRCP shows this, then the next step would be an ERCP to remove it.
Hello and welcome to the forum. Thanks for our question! So, I'm providing a link regarding possible causes of this. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886359/ Please copy and paste that into your browser. There are some potential reasons that could be concerning but it is important not to worry until you know something more. When is our MRCP scheduled? Things that can cause it are an obstruction of the biliary tree, which can be due to stones, tumors (usually of either the papilla of Vater or the pancreas), benign strictures (due to chronic pancreatitis or primary sclerosing cholangitis), benign stenosis of the papilla (ie, papillary stenosis), or a papillary diverticulum. Basically, when bile can't pass through, the duct becomes distended. So, an obstruction is likely causing it. Your doctor will need to determine the source of the obstruction. Something as simple as gallstones can cause it r even just inflammation of the duct. Here is a more user friendly article to read https://www.healthline.com/health/bile-duct-obstruction#types-of-bile-ducts. Please let us know what your doctor finds!