Chondroblastoma with Pulmonary Metastasis
Chondroblastoma with Pulmonary Metastasis
Clinical Scenario
A 16-year-old male presents with 8 months of right knee pain localised to the proximal tibia. The pain is activity-related and worsening. He is a school athlete (basketball) and is struggling to continue training. There is no history of trauma.
History:
- 8-month progressive knee pain
- Activity-related, improving with rest
- No night pain or constitutional symptoms
- No previous bone lesions or tumours
- No family history of malignancy
- Skeletally immature (open growth plates)
Examination Findings:
- Localised tenderness over proximal tibial epiphysis
- Mild soft tissue swelling, no warmth
- Full knee range of motion with terminal flexion pain
- No joint effusion
- No regional lymphadenopathy
- Normal neurovascular examination
- Contralateral knee normal
Investigations
Laboratory Results
Imaging
Plain X-ray Right Knee:
- Well-defined lytic lesion in proximal tibial epiphysis
- Thin sclerotic rim (geographic pattern, Lodwick 1A)
- Fine stippled calcification within lesion ("chicken-wire" pattern)
- Extends to subchondral bone
- Open proximal tibial physis
- No periosteal reaction
MRI Right Knee with Gadolinium:
- 2.5 x 2.0 x 2.2 cm well-defined epiphyseal lesion
- T1: Low-intermediate signal
- T2: Heterogeneous signal with low signal areas (calcification)
- Significant surrounding bone marrow oedema extending into metaphysis
- Enhancement with gadolinium (solid enhancement)
- No joint effusion
- Lesion abuts but does not cross physis
- Articular cartilage intact
CT Chest (Staging):
- Two small pulmonary nodules (8mm and 5mm) in right lower lobe
- No mediastinal lymphadenopathy
- No other pulmonary abnormalities
Histopathology
Core Needle Biopsy Result:
- Sheets of chondroblasts with distinct cell borders ("cobblestone" pattern)
- "Chicken-wire" calcification around individual cells
- Giant cells present (less numerous than GCT)
- No significant atypia or mitotic activity
- Immunohistochemistry: S100+, SOX9+
- Diagnosis: Chondroblastoma
Questions & Model Answers
What is your diagnosis and how do you explain the pulmonary nodules?
What are the characteristic imaging and histological features of chondroblastoma?
What is your biopsy approach for this lesion?
How would you treat the primary lesion in the proximal tibia?
How would you manage the pulmonary metastases?
What is the differential diagnosis for an epiphyseal lesion, and what is the prognosis for this patient?
Key Teaching Points
| Concept | Detail |
|---|---|
| Classic Location | Epiphysis of long bones before skeletal maturity |
| Pathognomonic Feature | Chicken-wire calcification (around cells, not in matrix) |
| Imaging Clue | Marked surrounding bone marrow oedema |
| Benign Metastases | 1-3% have pulmonary nodules - observe, don't panic |
| Treatment | Extended curettage with adjuvant, bone graft |
| Recurrence | 10-35%, successfully treated with re-curettage |
| Prognosis | Excellent - death extremely rare |
Common Examiner Follow-up Questions
-
"What is the difference between chondroblastoma and GCT?"
- Chondroblastoma: epiphyseal, skeletally immature, S100+, chicken-wire calcification
- GCT: epiphyseal-metaphyseal, skeletally mature, CD68+ giant cells, soap bubble
-
"What other benign tumours can metastasise?"
- Giant cell tumour of bone (2-3% pulmonary)
- Pleomorphic adenoma of salivary gland
- Pulmonary behaviour generally indolent
-
"What is clear cell chondrosarcoma?"
- Malignant cartilage tumour that mimics chondroblastoma
- Occurs in adults (usually >25 years)
- Epiphyseal location
- More aggressive radiographic features
- Requires wide resection
-
"What if the lesion recurs multiple times?"
- Re-curettage first attempt
- Consider more aggressive adjuvant
- En bloc resection for multiply recurrent lesions
- Joint replacement/fusion may be required