[Electron microscopic and immunohistochemical studies on chondroblastoma]

Six clinically and patho-histologically proven cases of chondroblastoma were studied with electron microscopic and immunohistochemical methods. The tumor tissues of chondroblastoma exhibited biphasic pattern i.e., chondroid and cellular area. In the chondroid area, small and round tumor cells contained many filaments in the cytoplasm and small processes in the cell wall. Many glycogen granules were present in the tumor cells in some cases. Intercellular matrix was immunohistochemically positive for S-100 protein and showed fine collagen fibers were very similar to those of articular and epiphysial cartilage. Many portions of mitochondria, cell wall and matrix of chondroblastoma tissue clearly exhibited calcification but were not definitely ossification. In the cellular area, tumor cells were composed of small immature mesenchymal and clear large degenerated tumor cells, histiocytes with lysosomes and osteoclast-like multinuclear giant cells. Immunohistochemical studies in the cellular area revealed that there were many tumor cells positive for lysozyme, alpha 1-antitrypsin and alpha 1-antichymotrypsin. In the transitional zone between chondroid and cellular area, degenerated tumor cells were found. The chondroblastoma was composed of chondroid and histiocytic areas which were very similar to those of chondromyxoid fibroma. The present study appears to demonstrate that chondroblastoma originates from a mixture of chondrocytic and histiocytic tumor cells but not from articular and epiphysial cartilage.