ACR Codes: 4.3
Osteosarcoma is defined as a malignant mesenchymal tumor where the cancerous cells produce bone matrix. It can occur in all age groups, but has a bimodal age distribution; 75% occur in patients younger than 20 years of age. Osteosarcoma can also arise in older adults in bones with long standing Paget's disease. It occurs 1.5 to 2 times more often in males than females.
The modal age of incidence is 16 for girls and 18 for boys. There are approximately 600 cases of osteosarcoma of the bone in children and young adults each year in the United States. The tumors usually arise in the metaphyseal region of the long bones of the extremities, almost 50% occur in the distal femur or proximal tibia. However, any bone can be involved. Many osteosarcomas develop at sites of greatest bone growth, where bone cell mitotic activity is at its peak.
The most common subtype of osteosarcoma is primary intramedullary, which is an aggressive poorly differentiated neoplasm that produces a predominantly osseous matrix. The tumors frequently destroy the overlying cortex and produce a soft tissue mass. The lesions on plain film have a poorly defined zone of transition with surrounding normal bone. They spread widely in the medullary canal, infiltrating and replacing the marrow.
The differential diagnosis can include: infection, Ewing's sarcoma, and chondrosarcoma. Patients typically present with painful and progressively enlarging masses. Pain can often be referred to the hip or back leading to delays in diagnosis. Pain is often attributed to trauma or vigorous physical exercise, both of which are common in the young population at risk.
These tumors can metastatize hematogenously to lung, bone, and brain. Diagnosis is primarily based on the radiographic appearance of the lesion. It is mandatory to obtain a biopsy for pathologic confirmation of the diagnosis. CT or MRI can help demonstrate the extent of involvement. CT is useful for defining cortical destruction and presence and extent of mineralized matrix. MRI is the modality of choice for defining intra-medullary and soft tissue extent. A bone scan is performed to look for metastases. CT of the lung is performed to detect pulmonary metastasis.
In the past surgical amputation was the rule and the outcome was poor. These tumors are also radio-resistant. Standard treatment now includes systemic presurgical chemotherapy for treatment of micro metastases and limb-salvage therapy for local control. Prognosis is determined by the patient's response to chemotherapy.
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