Figure 9b. Dedifferentiated chondrosarcoma in a 66-year-old man. (a) Contrast-enhanced CT scan at the level of the pulmonary artery (P) shows a mass with peripheral calcification (arrow) arising from the costovertebral joint and expanding into the thoracic cavity. Note the small pleural effusion. (b) Axial T2-weighted (4,500/97.7) MR image at the level of the pulmonary artery shows a tumor with heterogeneous high signal intensity extending into the thoracic cavity and invading the vertebral pedicle (curved arrow). The MR image better depicts the tumor extension in the rib (straight arrow) than does the CT scan. The pleural effusion had increased in size by the time of MR imaging.