Right arm posterolateral intramuscular irregular and infiltrative soft tissue mass lesion infiltrating the brachialis and the lateral head of the triceps muscles. The lesion elicits heterogeneous low/intermediate T1, high to intermediate T2, and STIR signal with internal bands of low signal. It is seen partially encircling the humeral shaft with no evidence of cortical invasion, marrow infiltration or periosteal reaction. The related subcutaneous tissue shows soft tissue stranding and scarring.