Unusual case of lipoma arborescens in the subacromial-subdeltoid bursa.

A 38-year-old female presented with a 10-month history of right shoulder pain with impingement symptoms. She was diagnosed on magnetic resonance (MR) imaging to have supraspinatus tendon tear and degenerative changes contributing to subacromial impingement. She also had lipoma arborescens of the subacromial-subdeltoid bursa, an uncommon condition in a particularly rare location. Lipoma arborescens is a benign intra-articular condition characterized by lipomatous proliferation of synovium with replacement of subsynovial tissue by mature adipocytes. It is typically a monoarticular process affecting the knee. Due to the presence of pathognomonic fat, diagnosis is usually straightforward with MR as the preferred imaging modality.