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from Chew: Musculoskeletal Imaging: A Teaching File
View PDF: Chew_Chap06 6
Clinical History: 6-year-old boy with pain and swelling at the knee for several months.
Findings: Lateral and AP radiographs of the knee. There is a large, destructive lesion involving the medial aspect of the distal femoral metaphysis, with cortical destruction and large soft tissue mass. The lesion extends to the growth plate but does not appear to cross into the epiphysis. Laminated, interrupted periosteal reaction is seen at the superior margin of the tumor. The margins of the lesion are poorly defined. Dense, amorphous regions of mineralization are present within the lesion.
Differential Diagnosis: Osteosarcoma, Ewing’s sarcoma, lymphoma, metastasis.
Diagnosis: Osteosarcoma, high-grade intramedullary type.
Discussion: This destructive lesion should be unmistakable for a bone tumor. The lesion is moderately mineralized, and the mineralization has the dense, amorphous, cloud-like pattern characteristic of osteoid matrix. The location of the lesion and age of the patient is typical for the diagnosis. The age distribution of osteosarcoma has a sharp peak (46% of cases) between the ages of 10 and 20, but it has been described in very young children and in elderly adults. Osteosarcomas have been described in virtually every part of the skeleton, but the least common sites are probably the hands and feet.
In the Mayo Clinic series of bone tumors , the most common anatomic sites of osteosarcomas were distal femur (31%), proximal tibia (15%), proximal humerus (8%), pelvis (7%), proximal femur (5%), and femoral shaft (4%). Of osteosarcomas that occur in the long bones, only about 10% are found in the diaphysis alone, without extension to the metaphysis or epiphysis. The majority of osteosarcomas have no known cause, but in this series, more than 5% were found in irradiated bone, and more than 3% were found in regions of Paget’s disease. Patients older than 60 are much more likely to have a preexisting condition (38%).