Premalignant lesions of the extrahepatic biliary tract. A territory to be explored hand in hand with cholangioscopy.

The biliary mucosa, both intrahepatic and extrahepatic, is lined by a single layer of columnar cells with oval nuclei near the base and a slightly eosinophilic cytoplasm. Although normal biliary ducts have no goblet cells, there are periductal mucous glands lined by mucus-producing cuboidal cells, with mucin from these glands draining to the lumen of bile ducts.