This patient was referred by his general practitioner for the appearance of a slowly enlarging mass on his right arm that had been present for 6 months with occasional paresthesia in the radial nerve distribution. He had no history of trauma and was otherwise asymptomatic. The patient presented 10 years ago for a lump in the medial aspect of his right upper arm which was subsequently excised and the diagnosis of Mazabraud syndrome was established following biopsy.

The imaging findings are similar to previously reported cases in the literature. MRI shows significant marrow signal abnormality throughout the humerus. In addition, a well-defined soft tissue mass, lying within the lateral aspect of the triceps muscle at the level of the midshaft of humerus appears of intermediate signal intensity on T1-weighted images, high signal intensity on the fat sat proton density images and exhibits some internal enhancement post-gadolinium.

A True cut needle biopsy was carried out and the histopathologic examination confirmed cores of skeletal muscle interfacing with an ill-defined myxocollagenous lesion displaying the features of an intramuscular myxoma.