Table 1 Main differences between myositis ossificans and osteogenic sarcoma

CLINICAL

Rapidly-growing, painful swelling and joint stiffness;

History of trauma.

Local pain, swelling and limp;

Night-time awakenings with bony pain;

Pathological fractures;

RADIOLOGICAL

Rx/CT: calcified peripherical rim with a radiolucent cleft between the lesion and the cortical bone.

Rx/CT: Periosteal reaction, Codman’s triangle, sunburst sign; lobulated mass (cauliflower-like).

MRI: early T2-weighted hyperintensity (oedema) and later hypointense rim in all sequences;

Usually no contrast-enhancement.

MRI: heterogeneous or solid contrast-enhancement.

HISTOLOGICAL

“zonal pattern organization”:

1. Peripherical mature lamellar bone;

2. Middle zone: immature osteoid matrix;

3. Inner zone: proliferating fibroblast tissue.

Spindle/polygonal, malignant mesenchymal cells; hemorrhagic and necrotic lesions;

MDM2 and CDK4 +.