Immunohistochemical and electron microscopic findings in a case of mixed hamartoma of the liver.

A case of mixed hamartoma of the liver in a 36 day old female infant is reported herein. The resected tumor was well demarcated, measured 7.5 X 7.0 cm and weighed 179 gm. Microscopically, the tumor was composed of loose fibrous stroma intermingled with spindle and polygonal cells and ductular structures. The spindle and polygonal tumor cells displayed the distinct cytoplasmic staining for alpha-1-antitrypsin. Most of the tumor cells showed the characteristic ultrastructural features of immature hepatocytes, having numerous cytoplasmic microvillous structures, abundant rough and smooth endoplasmic reticulum and mitochondria. These findings suggest that embryonic liver cells, which are capable of transforming into biliary structures and hepatocytes, serve as essential elements of mixed hamartoma of the liver.