[A case of orbital mesenchymal chondrosarcoma].

A 22-year-old male presented with proptosis of his right eye of one month's duration. No abnormalities were present regarding visual acuity, ocular motility, or fundus findings. Systemic examinations gave negative results. An orbital tumor, 25 mm in size, was detected by computed tomography and magnetic resonance imaging in the affected side. The tumor was located nasal-posterior to the eyeball and appeared to be in apposition with the orbital floor. The tumor was removed through a maxillary sinus approach. Histopathological studies led to the diagnosis of extraskeletal mesenchymal chondrosarcoma. To the best of our knowledge, this is only the fifth case reported in Japan of mesenchymal chondrosarcoma. Originating in the orbit.