Papillary cystic tumor of the liver. A case report with ultrastructural observation.

A case of primary tumor of the liver with pathologic features strikingly similar to those of the papillary cystic tumor of the pancreas in a 41-year-old woman is presented. Two large, well-demarcated, solid and cystic tumors with extensive hemorrhage and necrosis were located in the right and left lobes, measuring 30 x 27 x 7.5 cm and 5.5 x 4.0 x 2.5 cm, respectively. Microscopically, both tumor masses showed two basic patterns of cellular arrangement. One was a papillary pattern with fairly prominent fibrovascular stalks covered with one to three cell layers of tall to cuboidal cells. The other pattern was that of solid growth with microcystic degeneration. Ultrastructurally, the tumor cells were polyhedral and their oval shaped nuclei were occasionally indented. The cytoplasmic organelles varied in amount, and immature cell junctions and intercellular spaces were rarely present. A few cells contained zymogen-like secretory granules and annulate lamellae. The pancreas was free of tumor. To our knowledge, this tumor is a unique clinicopathologic entity of hepatic origin, and its similarity to the pancreatic papillary cystic tumor in clinical, gross, microscopic, and ultrastructural features together with their closely related organogenesis, suggests that this tumor derives from pluripotential cells transdifferentiating toward the pancreatic acinar cells and ductular cells, with the latter being indistinguishable from intrahepatic small bile ductular epithelial cells.