There is a well-circumscribed intramuscular mass within the distal aspect of the lateral head of the triceps muscle, probably arising from an intramuscular branch of the radial nerve. It is T1 isointense (to muscle) and T2 hyperintense, with a central T2 low signal ('target sign') and a thin rim of surrounding fat ('split-fat sign'). It demonstrates poor central enhancement. No other mass lesions. The median and ulnar nerves are unremarkable.
Small elbow joint effusion noted, with no evidence of synovitis. Small pseudo-defect of the capitellum noted. Prominent red marrow within the imaged humeral shaft and proximal ulnar and radius.