Ultrastructural and histochemical identification of sclerosing liposarcoma

A paratesticular tumour by light microscopy showed large amounts of partly hyalinized collagenous stroma, spindle shaped fibroblast-like cells, pleomorphic cells with foamy cytoplasm, multinucleated tumour type giant cells and lipid inclusions. By light microscopy, there was a problem as to whether the tumour should be classified with the liposarcomas or with the fibrous histiocytic group. Ultrastructurally, spindle shaped cells resembled fibroblasts and, in a few cells, intracellular collagen fibres were seen. Histochemical studies revealed the presence of mannose-rich glycoprotein which is characteristic for collagen producing cells, but frequently these cells also showed numerous lipid inclusion. The foamy cytoplasmic areas of pleomorphic cells were shown to consist of dilated ergastoplasmic sacs and large vacuoles lined by smooth endoplasmic reticulum negating the possibility that these cells were of histiocytic origin. This is supported further by the dearth of lysosomes and absence of lysozyme (muramidase) in the tumour cells. The presence of numerous lipid inclusions in many of the tumour cells, which are otherwise ultrastructurally similar to fibroblast, suggests that these cells represent precursors of lipoblasts. The above findings taken together allowed the tumour to be categorized as a sclerosing liposarcoma.