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Dedifferentiated chondrosarcoma is a highly malignant variant of chondrosarcoma. Approximately 11% of chondrosarcomas can be expected to dedifferentiate into more anaplastic lesions. Radiographic evidence of a benign-appearing cartilage lesion adjacent to a lytic, highly aggressive lesion suggests dedifferentiation. Despite radical surgical treatment, the prognosis is unfavorable, with a 5 year survival rate of 10%.

An illustrative case report of intraosseous ganglion cyst is presented. Intraosseous ganglion cysts are uncommon, juxta-articular, and benign. They are thought to arise from an intramedullary metaplastic event. Intraosseous ganglia are most common in middle-aged patients. They usually involve the tibia but also are located in other skeletal sites. The lesion is typically epiphyseal and appears benign. It is successfully treated with curettage and bone graft if it is symptomatic or progressively increasing in size. It is important to avoid extensive surgical procedures. Recurrence is unlikely.