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Primary malignant bone tumors, whether Ewing sarcoma or osteosarcoma, are a rare type of tumor. The sequential occurrence of two bone sarcomas, Ewing sarcoma and high-grade osteosarcoma, in the same patient at two different locations is an exceptionally rare phenomenon. We present the case of a 13-year-old girl who presented with a high-grade osteoblastic osteosarcoma of the distal femur, 7 years after treatment for Ewing sarcoma of the left pelvis. She did not receive radiation therapy. Following the recent developing multidisciplinary therapy, long-term follow-up for monitoring latent treatment-related adverse effects may be necessary for survivors of primary malignant bone tumors.

Lipoprotein lipase (LPL) deficiency is an extremely rare congenital metabolic disorder with an accumulation of chylomicrons in the blood. We encountered a patient with an LPL deficiency leading to multiple bone xanthomas associated with hyperlipidemia. Radiographs and MRI of the humerus and femur revealed symmetrical bone lesions, and there is a possibility that these symmetrical lesions may therefore be a characteristic feature for this disorder.

Desmoplastic small round cell tumor (DSRCT) is a rare malignant neoplasm typically involving the abdominal cavity of a young male. Extra-abdominal occurrence of this tumor is very rare. We report a 10-year-old girl with primary DSRCT arising within the left femur. The patient presented with knee pain, and radiological findings were strongly suggestive of osteogenic sarcoma. In addition to the typical microscopic appearance and immunophenotype, RT-PCR demonstrated the chimeric transcript of EWS-WT1, which is diagnostic of DSRCT. Pulmonary metastases were present at initial staging studies, but no abdominal or pelvic lesion was present. Despite chemotherapy and complete tumor excision, the patient developed progressive lung and bone metastases and died 3 years after initial presentation. This is the second reported case of primary DSRCT of bone with genetic confirmation.

Osteoblastoma-like osteosarcoma is a rare variant of osteosarcoma occurring in this instance in a highly unusual location: the lateral femoral condyle of a 13-year-old girl. The radiological features were non-aggressive and, although slightly unusual, were most suggestive of chondroblastoma.

Malignant giant cell tumor is a confusing term that in the past has been used to describe different types of giant cell-rich tumors. We try to clarify this term in this report. We consider two types of malignancy in giant cell tumor of bone: "primary" when it arises in juxtaposition to a benign giant cell tumor and 'secondary' when it arises at the site of a previously treated giant cell tumor. Here we present a case of primary malignancy in giant cell tumor that was initially not recognized as a malignancy. On radiography and histology of frozen sections the lesion had the appearance of a conventional giant cell tumor of bone. After curettage, the permanent histology slides showed areas of highly malignant osteosarcoma juxtaposed to areas of benign giant cell tumor. The patient was treated with chemotherapy and wide resection of the tumor.

We report a case of a 32-year-old woman who presented with parosteal osteosarcoma of the distal femur with simultaneous dedifferentiation to a high-grade osteoclast-rich osteogenic sarcoma. This pattern of dedifferentiation is rare, particularly at the time of presentation. We are aware of three other somewhat comparable cases in the literature; however, none is quite similar to our case.

We present the clinical, radiographic and pathological features of a juxtacortical chondrosarcoma which underwent dedifferentiation to an osteosarcoma in a 47-year-old woman. The tumour, abutting the femoral diaphysis, had initially presented 20 years earlier. Local excision was performed at presentation and again 10 years later, but the tumour recurred on each occasion. Serial radiographs showed cortical saucerisation evolving to cortical buttressing and mounding. After 20 years a dramatic radiographic change heralded tumour dedifferentiation.

Cryotherapy is an increasingly popular mode of therapy adjunctive to surgical curettage in the treatment of certain skeletal neoplasms, such as giant cell tumors or chondrosarcomas. The magnetic resonance (MR) findings following cryotherapy have not been previously reported. We reviewed the MR findings in seven patients with skeletal neoplasms following curettage and cryotherapy. In six cases we found a zone of varying thickness extending beyond the surgical margins, corresponding to an area of cryoinjury to medullary bone. This zone displayed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, consistent with the presence of marrow edema. This zone of edema almost certainly reflects underlying thermal osteonecrosis. This zone may vary in size and intensity over time as the area of cryoinjury evolves or resolves. MR is currently the imaging procedure of choice for follow-up of most musculoskeletal neoplasms. Knowledge of the MR findings following cryotherapy should help prevent confusion during the interpretation of follow-up MR examinations.

The clinical and radiographic findings in 104 patients with chondroblastoma are presented. Pain was an almost constant presenting complaint, often accompanied in the case of para-articular lesions by impaired function of an adjacent joint. The majority (80%) were in long bones with a mean age of presentation of 16 years. The characteristic radiological image of these lesions was an eccentric radiolucency, having a sharply defined sclerotic margin and containing areas of calcification in approximately a third of cases. They were always related to a growth plate. Nearly half were confined to the affected epiphysis or apophysis itself, but most of the remainder had traversed the growth plate to involve also the adjacent metaphysis. The bones around the knee and the proximal ends of the humerus and femur were the sites of predilection. A minority (20%) affected flat bones and short tubular bones of the hand and foot, with a peculiar affinity for the calcaneus and talus. The mean age of presentation of these was 28 years. The radiological pattern was similar, except for a greater tendency to expand the affected bone. Complications included the formation of a secondary aneurysmal bone cyst in 16 cases (10 of them in long bones), one malignant chondroblastoma, and one fibrosarcoma developing after radiation of the original chondroblastoma.

Fourteen telangiectatic osteosarcomas are reported. They are rare, clinically and radiologically aggressive lesions, involving mainly the femurs of young patients, often misdiagnosed as aneurysmal bone cysts. An explanation for a characteristic early radiological appearance consisting of regular parallel striations of the shaft is suggested.