Bilateral lipoma arborescens of the subdeltoid bursa.

Lipoma arborescens is a rare cause of chronic monoarticular arthritis. It is most commonly seen in the knees, but only a few cases involving other joints, especially the subdeltoid bursa, have been described. To our knowledge, this is the first reported case of lipoma arborescens involving bilateral subdeltoid bursae. Although it is associated with joint effusion, synovial cysts and erosions, the presence of reactive bone formation has not been reported. Magnetic resonance imaging is a very effective method for the diagnosis of this rare condition because of its ability to do tissue characterization.