Chondrosarcoma arising in osteochondroma. A, Radiograph reveals irregular ossification throughout exostosis of distal femur. B, T1-weighted coronal image shows hypointense marrow signal within lesion and extension of this abnormal signal into medullary canal of femur (arrows). C, Axial fat-suppressed, T2-weighted image demonstrates typical hyperintensity of neoplastic tissue (arrows), in contrast to surrounding normal tissues.