Epithelioid hemangioendothelioma of the liver: an ultrastructural study

Epithelioid hemangioendotheliomas are uncommon vascular tumors, mainly observed in lung and soft tissues. Liver involvement is infrequent and, in contrast to the extrahepatic localizations of the tumor, has not been subjected to detailed ultrastructural analysis. This prompted us to report the results of the ultrastructural study of three cases of epithelioid hemangioendothelioma of the liver. Neoplastic proliferation was heterogeneous. Most of neoplastic cells presented features suggestive of endothelial differentiation, including presence of Weibel-Palade bodies and evidence of vasoformative properties demonstrated by formation of both intra- and extracellular vascular channels resembling the normal structures successively observed during embryogenesis and tissue regeneration. A minor cell population, unreported so far, exhibited ultrastructural characters resembling those of pericytes and presented organoid relationship to neoplastic endothelial cells. Tumor spreading along sinusoids induced pseudopeliotic dilatations and led to a progressive disruption of normal liver architecture. In conclusion, the three cases of hepatic epithelioid hemangioendothelioma examined in this work assume many organoid features mimicking the successive steps of normal angioformation and indicative of a high degree of morphological differentiation.