What's the Diagnosis - Case 14

History 87 year old woman with left hip pain and states no recent trauma.

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Findings MRI of 6/08 demonstrates right gluteal mass which was asymptomatic. There is prominent edema pattern in the adjacent musculature. Radiograph demonstrates no right sided gluteal mineralization and ORIF of the left femur. Ultrasound shows a heterogeneous mass with prominent posterior acoustic shadowing. The second image is of an US guided needle biopsy. Comparison axial images from 6/08 and 7/08 demonstrate early peripheral mineralization of the mass.

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Diagnosis: Myositis Ossificans Muscle that has sustained trauma undergoes a process of formation of ossification in the musculature. In the first 8 weeks following the injury on MRI, a heterogeneous mass is frequently seen with a profound amount of surrounding edema. With time, a peripheral low signal intensity rim forms corresponding to peripheral ossification. In its early forms, the peripheral ossification may have a somewhat amorphous appearance on CT or radiograph without clear trabecular formation.

Frequently, patient’s do not recall a discrete event and with aging, less significant trauma is needed to cause these changes. Ultrasounds is useful to demonstrate acoustic shadowing indicating a dense substance, often calcification, ossification, or marked fibrosis. Ultrasound can also be used, as in this case, for biopsy to confirm the diagnosis.

Special thanks to the Department of Pathology for their assistance in this diagnosis.

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Resources • Resnick, D and Kransdorf M.Bone and Joint Imaging. 3rd Edition. 2005.

• Kaplan, P; Helms, C; et al. Musculoskeletal MRI. 2001.

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http://www.emedicine.com/PED/topic1538.htm

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http://en.wikipedia.org/wiki/Myositis_ossificans

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