Hepatocellular Adenoma of the Placenta With Updated Immunohistochemical and Molecular Markers

We describe the clinicopathological, immunohistochemical, and molecular features of an unusual case of a hepatocellular adenoma of the placenta presenting as a subchorionic intervillous mass lesion in a diamnionic dichorionic placenta. A well-circumscribed 0.8 cm round nodule was identified in one of the twin placental discs, wherein, on microscopic review, the lesional cells morphologically and immunophenotypically resembled fetal hepatocytes. Given the rarity of this lesion, we performed an updated immunohistochemical and molecular analysis, including makers for β-catenin activation and well-differentiated hepatocellular carcinoma, and the results support the notion that hepatocellular adenoma of the placenta is a benign incidental finding.