Background Myositis ossificans circumscripta (MOC) is a focal benign heterotopic ossification in musculoskeletal tissues, often occurring in young adults. Early stages of MOC may be mistaken for infection or malignancy. Since magnetic resonance (MR) imaging has now a key role in the diagnosis of soft tissue masses, MR features of MOC have to be recognised.
Objectives To compare the different features of MOC, as shown by the different imaging modalities (plain radiographs, computed tomography (CT) and MR examinations).
Methods 19 cases (M/F: 0.9, mean age: 32 years) of MOC from several hospitals in Paris were retrospectively studied with a special focus on imaging features. Diagnosis of MOC was based upon clinical and radiological criteria. Pathological examination was also obtained for 6 patients. The lesions were analysed for margin definition, MR signal intensity, surrounding oedema and contrast enhancement.
Results Post contrast enhancement was observed in the peripheral typical rim-like ossification, whatever the stage of the MOC. Enhancement of the calcified rim in mature lesions was an unexpected finding, since, to our knowledge, no mature calcified or ossified musculoskeletal lesions disclose such enhancement. The surrounding oedema was frequently observed on CT or RM examinations. It appeared in 3 patients as uncommon concentric intramuscular streaks. Oedema extension did not correlate with the early or mature stage of MOC. Synovitis or articular effusion were seen for 4 patients when MOC was located close to a joint.
Conclusion In this study, imaging patterns of MOC, specially MR imaging, could be analysed. Interestingly, original findings could be observed, which could help early diagnosis, thus avoid needless invasive procedures.
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