Metaphyseal bone lesions
Physiological basis
- Vascularity: Rich blood supply (terminal loops of nutrient arteries).
- Consequence: Predilection for haematogenous spread (metastasis, infection).
- Growth: Area of highest metabolic activity and turnover.
- Consequence: Site of origin for most primary bone tumours (osteosarcoma, chondrosarcoma).
Differential diagnosis approach
Diagnosis relies on age + position (central vs eccentric) + matrix.
A. Non-aggressive / benign ("leave me alone" lesions)
| Lesion | Position | Typical age | Key imaging features |
|---|---|---|---|
| Simple bone cyst (UBC) | Central | < 20 | • "Fallen fragment" sign (pathognomonic) • Truncated cone shape • No periosteal reaction unless fractured |
| Non-ossifying fibroma / FCD | Cortical / eccentric | < 30 | • "Bubbly" lytic lesion with sclerotic rim • Distal femur/proximal tibia • Migrates away from physis with growth |
| Chondromyxoid fibroma (CMF) | Eccentric | 10–30 | • Lytic, lobulated, sclerotic rim • "Bite" out of the bone |
| Enchondroma | Central | 20–50 | • Chondroid matrix (rings & arcs) • Scalloping of endosteum < 50% depth |
| Brodie's abscess | Central / eccentric | < 25 | • Lytic with thick sclerotic rim • Penumbra sign (T1 hyperintense rim on MRI) indicating granulation tissue • Thai context: Always rule out TB |
B. Aggressive / malignant / locally invasive
| Lesion | Position | Typical age | Key imaging features |
|---|---|---|---|
| Osteosarcoma | Central / eccentric | 10–25 | • Sunburst / Codman's triangle • Osteoid matrix (cloud-like) • Variant: Telangiectatic osteosarcoma (fluid-levels) |
| Aneurysmal bone cyst (ABC) | Eccentric | < 20 | • Fluid-fluid levels (MRI/CT) • Expansile "blown out" cortex • Can be primary or secondary to GCT/osteoblastoma |
| Giant cell tumour (GCT) | Eccentric |
20–40 (Closed physis) | • Abuts articular surface (subchondral) • Non-sclerotic margin • "Soap bubble" appearance |
| Chondrosarcoma | Central | > 40 | • Deep endosteal scalloping (>2/3) • Cortical breakthrough + soft tissue mass • Popcorn calcification |
| Metastasis / myeloma | Any | > 40 | • Moth-eaten/permeative • No sclerotic rim (unless prostate/breast/treated) |
High-yield exam pearls
The "fluid-level" trap
Fluid-fluid levels are not specific for ABC.
DDx:
- ABC (primary)
- Telangiectatic osteosarcoma (must biopsy viable tissue, not fluid)
- GCT (secondary ABC formation)
"Do not touch" lesions
If a metaphyseal lesion is:
- Eccentric
- Cortically based
- Sclerotic rimmed
- Asymptomatic
It is almost certainly a NOF. Do not biopsy.
Infection mimicry
In the Thai Board exam, a solitary metaphyseal lytic lesion with a sclerotic rim in a child is Brodie's abscess until proven otherwise.
- Look for a serpiginous tract extending toward the physis.
