A 15-year-old boy has chronic knee pain. Radiograph shows a well-defined lytic lesion centred in the proximal tibial epiphysis abutting the articular surface, with a thin sclerotic margin and no matrix calcification. MRI shows surrounding marrow and soft tissue edema disproportionate to the small lesion size. The most likely diagnosis is:
- A Osteoid osteoma
- B Giant cell tumour
- C Chondroblastoma ✓
- D Brodie abscess
Explanation
Chondroblastoma is a benign cartilage tumour that characteristically arises in the epiphysis or apophysis of skeletally immature patients, most often around the knee and proximal humerus. It appears as a well-defined lytic lesion with a sclerotic rim, may contain chondroid calcification, and is notable for edema of adjacent marrow and soft tissues that is out of proportion to lesion size. Giant cell tumour occurs after physeal closure in young adults, osteoid osteoma is diaphyseal or metaphyseal with a nidus and night pain, and Brodie abscess usually has a more irregular margin with a sinus tract.
Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.