Answer: Hepatobiliary cystadenoma

Histology: The cyst wall is thin, and in some areas the epithelium is denuded. However, focally, one can see a cellular ovarian type stroma underlying a benign glandular epithelium. These are the typical features of Hepatobiliary Cystadenoma. A similar tumor was resected from this patient 15 yeears ago.

Discussion: Choledochal Cysts are typically unilocular, as opposed to Hepatobiliary Cystadenomas which are typically multilocular. Choledochal Cysts have either benign glandular lining or may become denuded. Importantly, they lack the ovarian type stroma seen in Hepatobiliary Cystadenomas. Biliary Papillomatosis is a diffuse papillary intraductal proliferation that may involve the biliary tree in its entirety. The absence of papillary epithelium in the current case excludes this possibility. Primary Sclerosing Cholangitis is an inflammatory disorder that may diffusely involve the biliary tree. One would expect to see concentric fibrosis obliterating the lumen of the bile ducts, and would not expect to see ovarian type stroma.

Hepatobiliary Cystadenomas may be viewed as the biliary analogy to mucinous cystic neoplasms of the pancreas. They may be seen in the gallbladder, but more frequently are found in the extrahepatic bile ducts or the liver. Microscopically, they are characterized by three layers; an inner, cuboidal biliary or gastric foveolar type epithelium, a more cellular ovarian-like stroma which labels immunohistochemically for estrogen and progesterone receptors, and outer, dense hyaline connective tissue. Only rarely does dysplasia or carcinoma develop within these tumors; most are benign.