This patient presented with a central biliary obstruction that is most concerning for a cholangiocarcinoma, but there are some clues that help to lead you to the correct diagnosis. First, notice the pancreatitis in the original CT mostly involving the pancreatic tail. This is due to autoimmune pancreatitis, which is often seen when you encounter autoimmune cholangitis. 

Second, while the degree of smooth wall thickening and enhancement of the common hepatic and intrahepatic bile ducts can be seen with periductal infiltrating cholangiocarcinoma, I would have expected some other features of an advanced cholangiocarcinoma - specifically, some enlarged regional/porta hepatis lymph nodes or even signs of peritoneal disease. Plus, long segment involvement of the common bile duct is fairly typical of autoimmune cholangitis. 

After the ERCP brushings/biopsy were negative for carcinoma, IgG4 levels were checked and found to be mildly elevated. Of note, this patient had substantially elevated CA 19-9, which kept the treatment team more concerned about cancer, prompting another biopsy of the central liver under ultrasound - also negative for cancer but with some nonspecific inflammatory findings. Following these negative biopsies, this patient underwent a trial therapy of steroids, with dramatic improvement of the biliary ductal dilation after about 2 months, confirming the presumptive diagnosis of IgG4-related cholangitis, pancreatitis, and hepatic pseudotumor.