Radiographic, CT, and MR imaging features of dedifferentiated chondrosarcomas: a retrospective review of 174 de novo cases.

Up to 11% of chondrosarcomas may undergo regional anaplastic change, resulting in a high-grade noncartilaginous sarcoma arising within a typically low-grade chondrosarcoma. Known as dedifferentiated chondrosarcomas, these tumors are highly malignant with a very poor prognosis. The most important factor affecting survival is an accurate preoperative diagnosis. Therefore, the ability to predict the possibility of dedifferentiation in a malignant cartilage tumor on the basis of imaging findings is critical to ensure adequate tumor sampling at the time of biopsy. Imaging findings at radiography, computed tomography (CT), and magnetic resonance (MR) imaging in 174 patients with dedifferentiated chondrosarcoma were reviewed to determine whether there are radiologic features that can help predict dedifferentiation. On approximately one-third of the radiographs, one-third of the MR images, and one-half of the CT scans, the tumors demonstrated bimorphic features (ie, distinctly different tumor features juxtaposed within the lesion), most frequently a dominant lytic area adjacent to a mineralized tumor at radiography and a large, unmineralized soft-tissue mass associated with an intraosseous chondroid-containing tumor at CT and MR imaging. In the initial evaluation of patients with a primary bone tumor, thorough evaluation of the radiologic features of the entire tumor is critical.