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Chest Radiographs
Magnetic Resonance Imaging
Gross Pathology Specimen
HistologyThere is a mass in the anterior mediastinum, manifested by a mediastinal contour abnormality on the frontal radiograph at the level of the manubrium, and lack of a clear retrosternal space on the lateral radiograph. No calcifications are noted.
Axial thoracic MR images (T1, fat-saturated T1, and post-gadolinium T1 images respectively) demonstrate a mass that appears centered at the manubrium, extending into the anterior mediastinum, displacing the great vessels posteriorly. This mass is isointense to muscle, contains septations, and has peripheral nodular enhancement.
Based on MRI findings, the differential diagnosis should be expanded to include a sarcoma arising form the muscle, or primary bone tumor such as chondrosarcoma or osteosarcoma. The "bubbly" appearance in this lesion favors chondrosarcoma over osteosarcoma.
A cross-section through the bone illustrates the distal sternal margin, the superior manubrial margin, and the tumor. Flecks of hemorrhage are visible, as are cuts removed for histological evaluation (right side). On low-powered microscopic view, skeletal muscle on the margin of the tumor is visible in the lower right corner of the image. The tumor itself (purple) produces a hyaline material that is abnormal cartilage, cellular with large nests of cells. At higher power, the cells are visibly atypical. They vary significantly from one to another, and it is common to see two nuclei in a single mass. The red foci are necrotic. Immunohistochemistry does not play are large role in the diagnosis of chondrosarcoma.
Radiology Discussion
Chondrosarcoma is a malignant tumor of cartilaginous origin. It can be a primary lesion but may also develop from a preexisting cartilaginous lesion (e.g., osteochondroma, enchondroma). Chondrosarcoma is most common in adults over 40 year of age and shows a 2:1 male:female predominance in incidence. Patients are usually clinically asymptomatic. Chondrosarcoma can be categorized by location (i.e., central, peripheral, juxtacortical), degree of cellular differentiation (i.e., low-, medium-, high-grade), and by unusual histologic features (e.g., mesenchymal, clear cell). Common sites of involvement include long tubular bones (50%), pelvis (23%), ribs (11%), vertebrae (10%), and sternum (2%).
On plain radiographs, chondrosarcoma is typically visualized as a destructive, lytic lesion. Extension into surrounding soft tissues is frequently seen. The characteristic chondroid matrix (rings and arcs) can be seen on radiographs (70%), but are better delineated by CT. The differential diagnosis depends on the visualization of the chondroid matrix. If a chondroid matrix is seen, the differential includes metastasis, enchondroma, and osteochondroma. If a chondroid matrix is absent, the differential should include metastasis, plasmacytoma, fibrosarcoma, malignant fibrous histiocytoma (MFH), infection, and other aggressive lytic lesions are included.
When comparing the features of chondrosarcoma to enchondroma, several features are highly suggestive of chondrosarcoma. These include deep endosteal scalloping (greater than 2/3 of cortical thickness), cortical destruction and soft tissue mass, periosteal reaction, and marked uptake of radionuclide on bone scan.
Chondrosarcoma of the sternum typically demonstrates heterogeneous signal on T1- and T2-weighted MRI and enhances with contrast; focal high T2 signal suggests necrosis. MRI is excellent for assessing extent and relationship to adjacent structures, although chondroid calcification is suboptimally visualized with this modality.
Grade I chondrosarcoma is characterized by mild hypercellularity, large vesicular nuclei, and small nucleoli; the five-year survival rate is 90%. Grade II displays moderately increased cellularity with a slightly poorer 5-year prognosis (81% survival). Grade III is much more rare than I or II and carries a 5-year survival rate of 43%. The hallmarks include marked hypertrophy, pleomorphism, and the presence of giant tumor cells.
Chondrosarcoma is most effectively treated with wide (5cm margin) surgical resection, including any synchronous metastatic lesions. Chemotherapy or radiation therapy may also be added. Treatment of chondrosarcoma of the sternum requires total sternotomy, followed by skeletal and soft tissue reconstruction. Poor prognostic factors include incomplete resection, the presence of metastatic lesions, local recurrence, and age greater than 50 years.
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