Myositis ossificans - thigh

Case contributed by Dr Angela Byrne

The CT scan demonstrates a curvilinear area of ossification lying adjacent to the lateral aspect of the mid left femoral shaft. The ossification appears to be contiguous with the shaft of the femur with no intervening fascial plane. The ossification appears quite mature, and is denser peripherally than adjacent to the femoral shaft. No associated periosteal reaction, or femoral cortical or medullary abnormality is identified. No adjacent soft tissue mass is noted. 


Heterogeneous T1 and T2 signal intensity abnormality is evident in the left vastus intermedius muscle at the site of the ossification noted on the prior CT scan. Areas of low signal intensity on both the T1 and T2 weighted sequences correspond to the ossification noted on the prior CT. Surrounding high T2 signal intensity abnormality is noted within the muscle. No signal intensity abnormality is noted within the cortex of the femur or within the medullary cavity and again no periosteal reaction is identified.

Heterogeneous enhancement of the lesion within the vastus intermedius muscle is noted post gadolinium enhancement. No abnormal enhancement is evident within the femur. No mass is identified in the region of abnormal signal intensity and enhancement.

Case Discussion

Findings are most in keeping with myositis ossificans.

The lack of signal intensity abnormality within the adjacent femur and lack of significant mass effect make a surface osteosarcoma less likely, however this cannot be entirely excluded.

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