Chondrosarcoma with dedifferentiated foci. A comparative and ultrastructural study.

The light and electron microscopic features of a well-differentiated chondrosarcoma with dedifferentiated foci (CDF) are compared with those of a poorly differentiated chondrosarcoma with spindle cell elements. The differentiation of this lesion from mesenchymal chondrosarcoma and from primitive multipotential primary sarcoma of bone is discussed. Ultrastructurally, the cells of the cartilaginous region of the CDF resembled those of the poorly differentiated chondrosarcoma and of the cartilaginous zones of an extraskeletal mesenchymal chondrosarcoma reported by Fu and Kay, and were characterised by an abundance of dilated endoplasmic reticulum and a scalloped and microvillous cell membrane. The stroma was devoid of mature crossbanded collagen fibers. The dedifferentiated portion was composed of mesenchymal-type cells surrounded by a relatively sparse matrix containing scanty mature collagen fibers; these cells resembled those in the cellular regions of the two previously documented mesenchymal chondrosarcomas but differed from the cartilaginous type cells in the cellular regions of the poorly differentiated chondrosarcoma.