A well-defined (3.5 x 4.5 x 10.2 cm) focal lesion of the arm. It is intramuscular, occupying the distal part of the brachialis muscle. It displays T1 and T2 hyperintensity with a signal loss on fat-sat sequences (fat signal).
Normal size and signal of the rest of the muscles of the anterior and posterior arm compartments. Normal marrow signal of the humeral shaft. The neurovascular bundles are non-involved.