Ultrastructural characteristics of a pleomorphic liposarcoma. A possible involvement of myofibroblast.

A pleomorphic liposarcoma originated from the epicardial fatty tissue was studied with an electron microscope. The transmission electron microscopic examination revealed fibroblastic, myofibroblastic and primitive mesenchymal cells. Fibroblastic cells characterized by irregular nucleus with abundant heterchromatin and dilated cisternae were most frequently encountered, and the myofibroblastic cells, secondly in frequency, contained bundles of microfilaments with occasional dense bodies and outlined by discontinuous thin basal lamina. The primitive mesenchymal cells had mainly oval nucleus and electron lucent cytoplasm with poorly to moderately developed cell organellae. Some of the multinucleated giant cells relatively frequently observed revealed the aggregates of filaments with dense bodies at the cell margin. Many of them, irrespective of cell types, contained lipid droplets in the cytoplasm with various sizes. These observations suggest that a pleomorphic liposarcoma, at least a few of them, might contain not only fibroblastic, primitive mesenchymal but also myofibroblastic tumor cells with morphological varieties.