Dedifferentiated chondrosarcoma

Findings

The anteroposterior radiograph of the pelvis shows a lytic, expansile lesion of the right acetabulum that extends into the ilium and superior pubic ramus with cortical breakthrough of the iliopubic line. There are coarse calcifications in the center of the lesion that represent the chondroid matrix, which is frequently a characteristic of chondroid tumors. Surgical fixation hardware is present from a remote traumatic acetabulum fracture (Figure 1).

CT images reveal a large heterogeneous mass erupting through the posterior cortex of the right pubic bone and occupying most of the right pelvis (Figure 2). Bony destruction and extensive areas of necrosis within the mass are typical features of these aggressive tumors.

Distant metastases were found by CT of the chest and magnetic resonance (MR) imaging of the cranium. In the chest, there are multiple bilateral soft tissue lung masses and a large pleural effusion. These were biopsy-proven dedifferentiated chondrosarcoma (Figure 3). An axial postgadolinium T1-weighted MR image of the brain shows multiple ring-enhancing masses that are most consistent with metastases (Figure 4).

Fine-needle aspiration of the mass (Figure 5) and subsequent biopsy (Figure 6) resulted in the pathologic diagnosis of dedifferentiated chondrosarcoma.

Discussion

Chondrosarcoma is a tumor that is composed of neoplastic, mesenchymally derived cartilaginous cells and, other than osteosarcoma, is the most prevalent myxoid tumor found in the skeletal system. Dedifferentiated chondrosarcoma occurs in approximately 11% of patients diagnosed with chondrosarcoma and is considered to be a histological subtype of this chondroid lesion.¹ The term "dedifferentiated" implies that a portion of cells from the chondrosarcoma have degenerated into a high-grade malignant form that is characterized by pleomorphism, anaplasia, hypercellularity, and increased mitoses. Dedifferentiated chondrosarcomas typically arise centrally in the medullary canal.² Imaging commonly provides evidence of both the cartilage tumor and the high-grade noncartilaginous component. There is usually an abrupt transition between these 2 tissue types.³ The cartilaginous component may contain irregular areas of lysis with endosteal scalloping and periosteal thickening. These areas may also contain minute foci of calcifications in a ringlike configuration. The sarcomatous component is grossly lytic. Lytic lesions may be detected by cortical perforation and possible extension, which can result in a large mass.⁴ Due to its locally invasive nature, high rates of recurrence, and metastatic seeding of the skeleton and lungs, dedifferentiated chondrosarcoma carries a grave prognosis. When the tumor is deemed operable, most patients are treated with wide-margin resection and adjuvant chemotherapy. Despite this therapy, most patients die within 1 year of diagnosis.²

CONCLUSION

Dedifferentiated chondrosarcoma is an aggressive subtype of chondrosarcoma that is characterized by a cartilaginous component and a highly lytic sarcomatous component. Radiographically, there is often an abrupt transition between these tissue types within the lesion. A core biopsy can be used to help distinguish this tumor from other, less aggressive tumors and benign bone lesions. These patients typically present with complaints of bone pain and restricted movement; their prognosis is poor.

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2. Kilpatrick SE, Pike EJ, Ward WG, Pope TL. Dedifferentiated chondrosarcoma in patients with multiple osteochondromatosis: Report of a case and review of the literature. Skeletal Radiol. 1997:26:370-374.
3. de Lange EE, Pope TL Jr, Fechner RE. Dedifferentiated chondrosarcoma: Radiographic features. Radiology. 1986:160:489-492.
4. Mercuri M, Picci P, Campanacci L, Rulli E. Dedifferentiated chondrosarcoma. Skeletal Radiol. 1995:24:409-416.