Chondroblastoma and Chondromyxoid Fibroma
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Direct answer
Chondroblastoma is a benign cartilage-forming tumour of the epiphysis, seen mainly in adolescents whose growth plates are still open, most often at the knee. Its radiograph shows a well-defined lytic lesion with a sclerotic rim, often with chicken-wire calcification in the matrix. Chondromyxoid fibroma is the rarer metaphyseal counterpart, and both tumours are usually treated by curettage with bone graft.
What you must remember
- Site: chondroblastoma lies in the epiphysis, most often the distal femur, proximal tibia and proximal humerus.
- Age: adolescents, with the growth plate still open at presentation in chondroblastoma.
- Radiograph: a lytic lesion with a sclerotic rim, and chicken-wire calcification in the matrix in many cases.
- Chondroblastoma histology: sheets of chondroblasts with round nuclei showing grooves, the coffee-bean appearance, plus scattered multinucleated giant cells.
- Chondromyxoid fibroma: a lobulated, myxoid tumour of stellate or spindle cells, classically in the metaphysis of the proximal tibia.
- Immunostaining: S-100 protein and keratin support the diagnosis, but histology with imaging decides it.
- Treatment: intralesional curettage with bone graft, with adjuncts such as phenol or cryotherapy used by some surgeons.
Where the exam tries to catch you
Most errors come from calling a benign epiphyseal tumour malignant or from confusing it with giant cell tumour.
- Trap: calling chondroblastoma malignant because it is locally destructive Correct: it is benign, although it can recur and very rarely undergoes malignant change.
- Trap: confusing chondroblastoma with giant cell tumour of bone Correct: chondroblastoma is epiphyseal in a skeletally immature patient with chicken-wire matrix, whereas giant cell tumour arises at the end of mature bone after the growth plate has closed.
- Trap: choosing wide resection for a classic chondromyxoid fibroma Correct: the tumour is benign, so intralesional curettage with bone graft is the standard approach.
Frequently asked questions
Where does chondroblastoma most commonly arise?
Chondroblastoma most commonly arises in the epiphysis of long bones, particularly the distal femur, proximal tibia and proximal humerus. It affects adolescents while the growth plate is still open. Its epiphyseal position helps distinguish it from metaphyseal lesions.
What is chicken-wire calcification in chondroblastoma?
Chicken-wire calcification is a fine, lattice-like pattern of matrix calcification seen on radiographs of chondroblastoma. It reflects cartilaginous matrix within the lesion. Its presence supports the diagnosis, although not every chondroblastoma shows it.
How does chondromyxoid fibroma differ from chondroblastoma on histology?
Chondromyxoid fibroma shows lobules of stellate or spindle cells in a myxoid matrix, whereas chondroblastoma shows sheets of round chondroblasts with grooved nuclei. Both tumours are benign and can be confused on small biopsies. Correlation with imaging and the site of origin is essential.
Why does chondroblastoma tend to recur after surgery?
Chondroblastoma tends to recur after surgery when curettage leaves residual tumour in the epiphysis, which is difficult to clear completely. Adjuvant measures such as phenol or cryotherapy are used by some surgeons to reduce recurrence. Follow-up imaging is advised for this reason.
Is chondromyxoid fibroma a malignant tumour?
Chondromyxoid fibroma is a rare benign tumour of cartilaginous origin that arises in the metaphysis, most often of the proximal tibia. It is not malignant, although it can be locally expansile. Curettage with bone graft is the usual treatment, and the diagnosis rests on histology with imaging.