HEPATIC (HEPATOCELLULAR) ADENOMA OF THE PLACENTA - A STUDY OF 4 CASES

Hepatic (hepatocellular) adenoma of the placenta is an extremely rare nontrophoblastic placental lesion of disputed histogenesis, four examp les 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; med ian, 24.5), ranged from 0.3 to 1.0 cm in greatest dimension. Two were found within the villous parenchyma and two in subchorionic locations. On cross section, two examples were tan to dark red nodules without n ecrosis or hemorrhagic foci, whereas two were not visible grossly. The lesions were composed of semidistinct lobules of cords and nests of p olygonal epithelial cells resembling fetal liver. Extramedullary hemat opoiesis was a constant feature. The lesional cells contained glycogen and were immunoreactive for cytokeratin, alpha-fetoprotein, alpha-1-a ntitrypsin, and carcinoembryonic antigen. Although the histogenesis of these lesions remains uncertain, an origin from displaced yolk sac el ements with hepatocytic differentiation is the most likely hypothesis. It is important to distinguish hepatic adenoma of the placenta from p lacental cell island, heterotopic adrenocortical nodule, chorangioma, and placental metastasis of maternal and fetal malignancies.