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The case of a 61-year-old woman with a surgically resected solitary cholangiocarcinoma of the liver is reported, where many discrete multiple bile duct hamartoma (MBDH) were also seen. The latter is a congenital lesion of the liver that potentially may be confused with widespread metastatic disease. The relationship between cholangiocarcinoma and MBDH was studied histologically by the use of an immunoperoxidase technique for cytokeratin. MBDH was strongly positive for cytokeratin, while the neoplasm showed this to a lesser extent, but a clear continuity between the MBDH epithelial cells and those of the neoplasm was demonstrated by the use of this technic. The potential use for the various cytokeratins in the differentiation of primary from secondary liver tumors, is discussed. This differentiation is a significant problem to the pathologist. Although cholangiocarcinoma may, on occasion, be associated with various congenital lesions of the bile ducts, the association with MBDH is extremely rare, this being only the third reported case.

An unusual case of solid hepatic hamartoma, which could not be correctly categorized under the WHO classification, is reported. The well defined, solid nodular lesion, arising in the anterior edge of the left hepatic lobe, was found in a 15-month-old female infant. The lesion was composed of irregularly shaped yellow islands of parenchyma and white-gray nodules of fibrous stroma of various sizes, which were intermingled revealing a mosaic pattern. Prominent bile ductal proliferation was observed histologically in the fibrous stroma, associated in parts with dense or loose periductal bundles and vascular proliferation. The stromal proliferation seemed to result in erosion of the islands of differentiated parenchymal cells with no regeneration. Alpha-fetoprotein was demonstrated immunohistologically in the parenchymal cells of the lesion. From these findings, the essential component of this solid hamartoma was thought to be markedly proliferating bile ducts associated with periductal fibrosis, resulting in a fibroadenomatous pattern.

An 8-month-old boy was found to have a solitary hepatic mesenchymal hamartoma. Histologically, the lesion appeared as a large island of loose mesenchymal tissue with few cystic bile ducts and liver cells. Electronmicroscopy showed microvilli on the surface of tumor cells and desmosomes between the cells. Immunohistochemical studies showed that alpha-fetoprotein was localized in the proliferating liver cells and bile ductal epithelium of this neoplasm. This case is the 17th case of hepatic mesenchymal hamartoma reported in Japan.