Proliferative myositis: expanding the differential diagnosis of a soft tissue mass in infancy.

Proliferative myositis, a pseudosarcomatous lesion of skeletal muscle, is quite rare in the pediatric population. While benign, it is not always recognized as such, and may be treated with an extensive resection that can result in permanent disfigurement. We report a case of an infant with the diagnosis of proliferative myositis, who to our knowledge is the youngest patient to be evaluated with magnetic resonance imaging (MRI). Although the MRI findings are non-specific, we highlight the importance of considering proliferative myositis in the differential diagnosis of a soft tissue mass, which ultimately might prevent an overly aggressive resection in a child.