MRCP "Persistent mild dilation of the central intrahepatic duct. There are areas of mild narrowing & irregularity of the intrahepatic ducts & proximal common duct. No dilation of common bile duct. Gallbladder sludge is present." What causes this?

Nonspecific. I believe that the ductal findings are nonspecific. Sludge in the gall bladder can cause abdominal distress and indigestion. A gastroenterologist would sit down with the radiologist and review the images and decide whether more imaging studies like an MRI or liver biopsy are advisable depending upon your symptoms or lack of symptoms.