Intracytoplasmic crystalloid structures in a malignant fibrous histiocytoma: ultrastructural and cytochemical study.

Crystalloid structures were frequently observed in the cytoplasm of the tumor cells of a malignant fibrous histiocytoma arising in the left leg of a 71-year-old female. These structures were located in the cytoplasm of the fibroblastlike and histiocyte-like tumor cells. The structures consisted of an aggregate of dense granules without unit membrane. Neither glycoproteins nor polysaccharides were detected in these structures on sections stained with chromic acid-phosphotungstic acid or periodic acid-thiocarbohydrazide-silver proteinate. On sections from acrylate-embedded specimens, the structures were easily digested by trypsin and protease but were not sensitive to RNase. Although the significance and origin of these structures remain obscure, the results indicate that the crystalloid structures in the present study are mainly composed of proteinaceous substance.