Pathological aspects of so called "hilar cholangiocarcinoma"

Cholangiocarcinoma (CC) arising from the large intrahepatic bile ducts and extrahepatic hilar bile ducts share clinicopathological features and have been called hilar and perihilar CC as a group. However, "hilar and perihilar CC" are also used to refer exclusively to the intrahepatic hilar type CC or, more commonly, the extrahepatic hilar CC. Grossly, a major distinction can be made between papillary and non-papillary tumors. Histologically, most hilar CCs are well to moderately differentiated conventional type (biliary) carcinomas. Immunohistochemically, CK7, CK20, CEA and MUC1 are normally expressed, being MUC2 positive in less than 50% of cases. Two main premalignant lesions are known: biliary intraepithelial neoplasia (BilIN) and intraductal papillary neoplasm of the biliary tract (IPNB). IPNB includes the lesions previously named biliary papillomatosis and papillary carcinoma. A series of 29 resected hilar CC from our archives is reviewed. Most (82.8%) were conventional type adenocarcinomas, mostly well to moderately differentiated, although with a broad morphological spectrum; three cases exhibited a poorly differentiated cell component resembling signet ring cells. IPNB was observed in 5 (17.2%), four of them with an associated invasive carcinoma. A clear cell type carcinoma, an adenosquamous carcinoma and two gastric foveolar type carcinomas were observed.