Biliary adenofibroma. A heretofore unrecognized benign biliary tumor of the liver.

Benign biliary tumors of the liver are uncommon. In this report, we describe a distinctive biliary tumor of 7-cm diameter occurring in the right lobe of the liver of a 74-year-old Chinese woman. The lesion, characterized by a complex tubulocystic nonmucin secreting biliary epithelial and an abundant fibroblastic stromal components, is distinct from other well-recognized biliary lesions. A number of unusual features are focally present, namely, intraluminal bile concretions, apocrine-like epithelial change, acute inflammation, and granuloma. The tumor shows a striking resemblance to Meyenburg's complex (MC), but the large size of the lesion and the absence of any typical MC in the background liver are exceptional for the latter. Its expansile growth, possession of mitoses, and foci of epithelial tufting and cellular atypia favor a neoplastic process. Previous reported cases of adenomatous neoplastic transformation of MC are dissimilar. We therefore conclude that this is a hitherto unrecognized biliary tumor that may be yet another neoplastic form of MC and propose the designation biliary adenofibroma. The course appears benign, but malignant epithelial transformation may supervene if the lesion is left untreated.