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Myositis Ossificans (MO) is a benign, heterotopic (extra-skeletal) ossification process occurring within soft tissues, typically skeletal muscle, following trauma.
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It represents a non-neoplastic, reactive proliferation of bone and cartilage and is characterized radiologically by a classic zonal pattern of ossification.
Pathological Phases
| Phase | Timeframe | Pathology | Imaging Findings |
|---|---|---|---|
| Early | 0–2 weeks | Cellular proliferation, edema | Soft tissue swelling, no calcification (US/MRI) |
| Intermediate | 2–4 weeks | Osteoid production | Ill-defined peripheral calcifications on X-ray |
| Mature | >6 weeks | Mature lamellar bone | Well-defined peripheral ossification with lucent center |
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Bbenign ossifying soft-tissue mass, emphasizing the zonal maturation pattern and peripheral calcification with central lucency, best seen in CT and plain radiographs
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| Modality | Imaging features |
|---|---|
| XR | • Peripheral, well-circumscribed calcification. |
| • Zonal phenomenon: Densely ossified rim with radiolucent center (reverse of malignancy). | |
| • Separated from adjacent bone (key differentiator from osteosarcoma). | |
| US | • Early: Heterogeneous mass with increased vascularity. |
| • Late: Hyperechoic rim corresponding to ossified periphery. | |
| CT | Best for identifying mature ossification and exact location relative to bone. |
| • Shows peripheral mineralization, sometimes with a lucent central zone. | |
| MR | • Early: Soft-tissue mass, high T2 signal, edema; may mimic soft tissue sarcoma. |
| • Late: Peripheral low signal rim on all sequences due to calcification/ossification. |
Common locations: