Slide 1
The basic disease process appears to be an intramedullary tumor of the metaphysis and distal diaphysis with extension through the cortical bone into the adjacent soft tissue. The cortex is ill-defined distally, suggesting osteolytic activity. The soft tissue component has a pattern of lines extending perpendicularly from the cortex that corresponds to the osteoblastic ("hair on end") pattern of bone formation seen in the radiograph. Grossly, this osteosarcoma does not appear to have penetrated the growth plate although they can, and often do. Epiphyseal invasion, even when present, is rarely evident to the radiologist.

Slide 2
Here are the typical radiographic features of an osteosarcoma. An ill-defined permeative mixed lytic and blastic lesion involving the distal femoral metaphysis. Note that the abnormality extends to the growth plate in this child. It is not uncommon for this lesion to cross the growth plate. Note the soft tissue mass, and "hair on end" spiculated periosteal reaction indicating rapid growth of this highly malignant tumor.