Chondrosarcoma is a slow-growing painful malignant bone tumour arising from cartilage cells, typically occurring in adults and characterised by endosteal scalloping greater than two-thirds of the cortical thickness on imaging.
Description
Chondrosarcoma is a malignant bone tumour that arises from cartilaginous cells. It is the second most common primary bone malignancy after osteosarcoma. The tumour is typically seen in adults, with a peak incidence in the fifth to seventh decades of life. Chondrosarcoma is characteristically slow-growing and often presents as a large, painful mass.
Pathogenesis
The exact pathogenesis of chondrosarcoma is unclear. It is believed to arise from the transformation of normal cartilage cells into malignant cells, which then proliferate and secrete malignant cartilage. Certain genetic abnormalities have been associated with the development of chondrosarcoma, including mutations in the IDH1 and IDH2 genes.
Subtypes
Chondrosarcomas can be divided into primary and secondary types, and each category has several subtypes:
Primary Chondrosarcomas: These arise de novo and account for about 90% of all chondrosarcomas.
- Conventional Chondrosarcoma: This is the most common subtype, accounting for about 85% of all chondrosarcomas. It is further divided into central, which arises from medullary bone, and peripheral, which arises from the periosteal surface. The central type is more common. Both types can be graded as I (low-grade), II (intermediate-grade), and III (high-grade) based on cellularity, nuclear size, and mitotic activity. Higher grades are associated with a higher risk of metastasis and recurrence.
- Dedifferentiated Chondrosarcoma: This subtype accounts for about 10% of chondrosarcomas. It is characterised by an abrupt transition from a low-grade cartilaginous tumour to a high-grade non-cartilaginous sarcoma, most often osteosarcoma or fibrosarcoma. This subtype has a poor prognosis, with a 5-year survival rate of less than 10%.
- Clear Cell Chondrosarcoma: This is a rare subtype, accounting for less than 2% of chondrosarcomas. It typically arises in the epiphyses of long bones and has a relatively good prognosis with a low rate of metastasis.
- Mesenchymal Chondrosarcoma: This is a very rare, highly aggressive subtype that frequently metastasises. It can arise in both bone and soft tissues.
Secondary Chondrosarcomas: These arise from pre-existing lesions such as osteochondromas or enchondromas. They typically demonstrate a higher grade than the pre-existing lesion and have a worse prognosis than primary chondrosarcomas.
Epidemiology, Risk Factors & Associations
- Chondrosarcoma represents 20-27% of all primary bone malignancies.
- Peak incidence occurs between the fifth and seventh decades of life.
- There is a slight male predominance.
- Previous radiation therapy and hereditary multiple exostoses are risk factors for developing chondrosarcoma.
Clinical Features
- Patients typically present with a slow-growing, painful mass.
- The tumour most commonly arises in the pelvis, femur, and humerus.
Complications
- Metastasis can occur, most commonly to the lungs and lymph nodes.
- Recurrence can occur, particularly in high-grade tumours.
Pathological Features
Histopathology
- Macroscopic: The tumour is typically firm and lobulated with a grey-blue appearance.
- Microscopic: Malignant chondrocytes are seen, often with areas of calcification or ossification.
Serology
- No specific serological markers.
Biochemistry
- Elevated alkaline phosphatase levels may be seen.
Radiological Features
General Features
- Location
- Primary: Arises within medullary cavity
- Secondary: Arises from cartilage cap of osteochondroma
- Characteristically demonstrates endosteal scalloping greater than two-thirds of the cortical thickness.
- May demonstrate a soft tissue mass with calcifications, often described as a “ring-and-arc” pattern.
XR
- Radiographs may demonstrate a lytic or sclerotic lesion with areas of calcification.
CT
- Non-contrast: Shows a lytic lesion with possible calcifications and cortical destruction.
- Contrast-enhanced: May show enhancement of the tumour and any associated soft tissue mass.
MRI
- T1WI: Lesion is typically hypointense.
- T2WI: Lesion is hyperintense with possible areas of low signal intensity due to calcification.
- T1 C+: There may be heterogeneous enhancement post gadolinium.
Grading and Staging
Grading is based on histological features and is divided into grades I, II, and III. The Enneking system is used for staging, which takes into account the histological grade, local extent of the tumour, and presence of metastasis.
Diagnosis
Diagnosis is made based on a combination of clinical presentation, imaging findings, and histological confirmation.
Differential Diagnosis
- Osteosarcoma: Usually affects younger patients, and typically demonstrates a “sunburst” pattern on imaging.
- Chondroblastoma: Usually affects younger patients and characteristically occurs in the epiphysis of long bones.
- Enchondroma: A benign cartilage tumour, typically smaller and without associated soft tissue mass.
Management
Management of chondrosarcoma typically involves wide surgical resection. Radiation therapy and chemotherapy are less effective due to the slow-growing nature of the tumour but may be used in certain cases, particularly for high-grade tumours.