Cystadenomas of the liver and extrahepatic bile ducts: Morphologic and immunohistochemical characterization of the biliary and intestinal variants.

Cystadenomas of the liver and extrahepatic bile ducts (EHBD) are uncommon but distinctive neoplasms whose terminology and epithelial phenotype have been a source of controversy. We reviewed 20 cases, 16 arising in the liver and 4 in the EHBD. Eighteen patients were women, with a mean age of 36.5 years. Eighteen tumors were multiloculated and 2 were unilocular. The tumor size ranged from 4 to 29 cm (average, 11 cm). The cyst fluid in 13 tumors was described as serous, in 2 as clear, in 2 others as hemorrhagic, and in 1 as serous and mucinous. Only in 2 tumors was the fluid described as mucinous. In 18 cystadenomas, the predominant epithelial lining consisted of a single layer of cuboidal or low-columnar nondysplastic cells similar to those of the gallbladder or bile ducts. This epithelial lining was strongly positive for cytokeratins 7 and 19, and focally positive for MUC1. Only 2 cystadenomas showed predominant intestinal differentiation characterized by mature goblet cells and columnar absorptive cells. These cells expressed CDX2, MUC2, and cytokeratin 20. Admixed with the goblet and columnar cells, there were serotonin-containing cells and Paneth cells. These 2 tumors showed extensive areas of high-grade dysplasia and invasive adenocarcinoma with intestinal phenotype. A subepithelial ovarian-like stroma was present in all tumors. None of the patients died of the tumors. We believe that the term mucinous cystic tumor recommended by the World Health Organization for all cystadenomas of the liver and EHBD is a misnomer.