A 40-year-old male weightlifter presented with a 6-month history of a painless mass in the right deltoid. He had no history of trauma to the shoulder other than an arthroscopic rotator cuff repair a few weeks earlier. Physical examination showed a firm, nontender mass located longitudinally and coinciding with the deltoid, measuring 12×14×4 cm. There was no limitation in range of motion or functioning. Magnetic resonance imaging (MRI) and computed tomography (CT) scans suggested a lobulated, heterogeneous mass with multiple areas of calcification that raised suspicion for soft tissue sarcoma vs myositis ossificans. Marginal resection of the soft tissue mass was performed, and pathologic studies confirmed the diagnosis of xanthogranulomatous myositis ossificans with dystrophic calcifications and central cystic degeneration. At 2-week follow-up, the patient had improved range of motion and pain, but he noted a second soft tissue mass in the left deltoid. The MRI and CT scans showed a 10.5×16×3.4-cm linear, lobulated lesion with multiple calcifications, similar in appearance to the contralateral deltoid. The patient admitted to frequently injecting anabolic steroids into his deltoids. Because the patient was asymptomatic on the left side and the MRI appearance of the left deltoid mass was similar to that of the myositis ossificans seen on the right side, the patient opted for nonsurgical treatment. This is a rare case of myositis ossificans occurring bilaterally in the deltoids after repeated injections of anabolic steroids. There is currently no known association between anabolic steroids and myositis ossificans. This condition often mimics malignant neoplasms, illustrating the necessity of resection for diagnostic confirmation.
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