Figure 6b. Periosteal reaction. (a) Frontal radiograph of a 9-year-old boy shows permeative changes of the distal femoral shaft with a dense periosteal reaction. (b) Lateral view clearly shows the laminated and interrupted periosteal reaction (arrow), a feature of round cell tumors including lymphoma and Ewing sarcoma. (c) Axial T2-weighted image (4,500/80) reveals the circumferential nature of the soft-tissue mass and abnormal marrow. Note disuse atrophy of muscles in the affected side.