Myxoid malignant fibrous histiocytoma versus myxoid liposarcoma. A comparative ultrastructural study.

An ultrastructural comparison of 7 examples of myxoid malignant fibrous histiocytoma (myxoid MFH) with 6 of myxoid liposarcoma is described. Despite certain histological differences between the two, electron microscopy was more valuable in differentiating MFH from liposarcoma. Electron microscopically, MFH contained a variety of cell types including histiocyte-like, fibroblast-like, intermediate-type, xanthomatous, multinucleated tumor giant cells and undifferentiated cells. Liposarcoma was composed mainly of lipoblasts at various stages of differentiation with a minority of undifferentiated cells and fibroblast-like cells. In contrast to the component cells of the MFH, these lipoblasts were characterized by abundant cytoplasmic glycogen, numerous pinocytotic vesicles and a discontinuous basal lamina in addition to large lipid droplets.