Figure 15b. Juxtacortical chondrosarcoma of the fibula in a 37-year-old man who had a painful lump in his right lower leg for 1 year. (a) Anteroposterior radiograph shows a soft-tissue mass with osteoid and chondroid mineralization between the tibia and fibula at the proximal diaphysis and extrinsic erosion of the fibula (arrows). (b) Axial CT scan reveals a mass with prominent mineralized matrix, low attenuation in the nonmineralized portion of the lesion (*) typical of cartilaginous neoplasms, and extrinsic erosion of the fibula (arrow) but no involvement of the marrow. (c) Axial T1-weighted (600/12) MR image demonstrates the low-signal-intensity juxtacortical lesion (M) adjacent to the proximal fibular diaphysis with extrinsic erosion (arrow) but no marrow involvement. (d) Sagittal T2-weighted (2,000/80) MR image demonstrates marked high signal intensity in the mass (M) and lobular margins (arrows) (see Fig 5).