A case of mesenchymal chondrosarcoma of the orbit.

A case of mesenchymal chondrosarcoma occurring in the right orbit of a 84-year-old Japanese female was reported. The ultrastructural findings of tumour are composed of three cell types: well-differentiated cartilaginous cells, undifferentiated cells and transitional cells. The well-differentiated cells showed scalloped cytoplasmic membranes, numerous mitochondria showing dense electron matrix, various size of lipid granules, and abundant amount of extracellular matrix. The extracellular matrix were collagen fibres and ground substances and matrix vesicle. The undifferentiated cells showed smooth cytoplasmic membranes, large nuclei resembling primitive mesenchymal cells.