Ultrastructure of infantile hemangioendothelioma of the liver.

A two-month-old female presented with hepatomegaly 5 cm below the right costal margin. Resection of a 6 cm hepatic mass demonstrated an infantile hemangioendotheliom (IHE). This documents for the first time the ultrastructural features of an IHE of the liver. Ultrastructural examination showed large numbers of vascular channels of varying sizes lined by abnormal endothelial cells. An incomplete basal lamina separated the endothelial cells from the extracellular material and there were no associated pericytes. The intervascular area contained abundant collagen fibers, fibrils, and cells ultrastructurally similar to fibroblasts. The relationship of structure to certain clinical features of this lesion is discussed.