Hepatic (hepatocellular) adenoma of the placenta: a study of four cases.

Hepatic (hepatocellular) adenoma of the placenta is an extremely rare nontrophoblastic placental lesion of disputed histogenesis, four examples of which were diagnosed over a 10-year period. The lesions, which were incidental findings in women 21 to 30 years of age (mean, 25; median, 24.5), ranged from 0.3 to 1.0 cm in greatest dimension. Two were found within the villous parenchyma and two in subchronic locations. On cross section, two examples were tan to dark red nodules without necrosis or hemorrhagic foci, whereas two were not visible grossly. The lesions were composed of semidistinct lobules of cords and nests of polygonal epithelial cells resembling fetal liver. Extramedullary hematopoiesis was a constant feature. The lesional cells contained glycogen and were immunoreactive for cytokeratin, alpha-fetoprotein, alpha-1-antitrypsin, and carcinoembryonic antigen. Although the histogenesis of these lesions remains uncertain, an origin from displaced yolk sac elements with hepatocytic differentiation is the most likely hypothesis. It is important to distinguish hepatic adenoma of the placenta from placental cell island, heterotopic adrenocortical nodule, chorangioma, and placental metastasis of maternal and fetal malignancies.