[A juvenile case of mesenchymal chondrosarcoma originating from soft tissue in the orbit]

Mesenchymal chondrosarcoma is a very rare occurrence in the orbit. A 10-year-old girl presented with right exophthalmos. Computed tomography revealed a round tumor inside the muscular cone of the right orbit. There was a sign of slight calcification inside the tumor. The tumor was surgically removed by the Krönlein-Berke procedure. Histopathological examination showed undifferentiated mesenchymal cells and cartilage tissue. A recurrent tumor was found in the same location 34 months after the surgery, which was removed by frontal approach saving the globe with normal function. Histopathology of the recurrent tumor revealed a slight difference from the primary tumor, showing hemangiopericytoma pattern without cartilage components. Immunohistochemical studies of the primary and recurrent tumors showed their cells to be positive for antifactor VIII and S-100, and negative for myoglobin and monoclonal antibody to muscle actin. Electron microscopically these undifferentiated cells had large nucleus and very scanty cytoplasm, mostly containing glycogen granules. This is probably the first description of a juvenile case of mesenchymal chondrosarcoma originating from soft tissue in the orbit.