Myositis ossificans requires multiple diagnostic modalities.

Myositis ossificans is a type of bone-forming lesion that arises in soft tissue and mimics malignancy. We present a case of myositis ossificans in a 16-year-old girl with anxiety disorder, Asperger syndrome, and no known history of trauma. A variety of diagnostic tools including magnetic resonance, ultrasound, and biopsy are used to make the diagnosis. The histologic and radiographic findings used to distinguish this disorder from malignant conditions are discussed.