Mesenchymal chondrosarcoma.A study of the ultrastructure

The ultrastructural findings in a case of mesenchymal chondrosarcoma are described. The tumor is composed mainly of 2 cell types: poorly differentiated cells, and cells showing cartilaginous differentiation. The poorly differentiated mesenchymal cells have sparsity of organelles. The tumor cells showing cartilaginous differentiation have a well-developed Golgi apparatus, glycogen, and rough endoplasmic reticulum, with occasional dilatation. The matrix of the tumor consists of thin collagenous fibrils, 90 to 350 A in thickness, and electron-dense material. We feel that mesenchymal chondrosarcoma originates from primitive mesenchyme; some areas of the tumor have remained in an early undifferentiated stage and others have undergone cartilaginous differentiation. It appears morphologically that the cartilage cells and their matrix are in an early stage of maturation. We feel that the vascular pattern, resembling hemangiopericytoma, is due to proliferation of undifferentiated tumor cells around vascular spaces rather than pericytes.