A mixed hamartoma of the liver: light and electron microscopy.

The gross, microscopic, and ultrastructural features of a mixed liver hamartoma occurring in a three month old infant are reported. The differentiation from two solid liver masses, focal nodular hyperplasia and liver cell adenoma is emphasized. Mesenchymal hamartomas, though usually cystic rather than solid masses, share the histologic feature of fibroductular tissue with mixed liver hamartomas and focal nodular hyperplasia. Only the mixed liver hamartoma has extremely broad fields of ductules and an embryonic type of hepatocyte at the ultrastructural level. These and other hepatic lesions show morphologic evidence of transformation of liver cells into biliary epithelial cells in association with vascular connective tissue.