Magnetic resonance imaging of myositis ossificans: analysis of seven cases.

Myositis ossificans typically presents as soft tissue swelling with progressive ossification on radiographs. Since magnetic resonance imaging (MRI) is commonly used to evaluate soft tissue masses, we analyzed eight MR examinations in seven patients with myositis ossificans to determine if typical patterns were present. One acute lesion had homogeneous intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Two subacute lesions had low signal intensity margins with slightly increased signal intensity centers on T1-weighted images and very high signal intensity on T2-weighted images. Five chronic lesions had two different patterns. All five were well-defined with low signal intensity borders. Three had signal intensity patterns characteristic of fat on T1-weighted and T2-weighted images. The other two lesions had intermediate signal intensity on T1-weighted images and slightly increased signal intensity on T2-weighted images. We conclude that typical MR appearances of myositis ossificans do exist. A low signal intensity rim is a common finding. However, these patterns are not unique to myositis ossificans and resemble those that have been reported in other lesions. It is important to be aware of the spectrum of MR findings of myositis ossificans when considering the differential diagnosis of a soft tissue mass.