Abstract
Introduction: Lipoma arborescens is a rare condition of unknown cause. It is characterized by proliferation of the synovium with replacement of the sub synovial tissue by mature fat cells. The knee joint is the most commonly affected. Involvement of other joints has been announced such as elbow and shoulder. Case presentation: We are describing a case of 49-years old female diabetic patient who came to the rheumatology dinic of King Khalid Hospital in Al-Kharj with a two-year history rheumatoid arthritis and treated with methotrexate. In addition, she had a right knee arthroscopy and synovectomy for "pigmented villonodular synovitis". Thereafter, the patient came in the outpatient dinic with a swollen knee. At examination, she has arthritis of the ankles and the wrists and a swollen right knee. Laboratory investigations show elevated inflammatory markers and normal liver and renal panels. An MRI of the right knee was ordered. Discussion and conclusion: In this case; we focus attention on is an extremely uncommon condition; lipoma arborescens. The dinical findings and imaging are characteristics by highlighting the role of MRI, in diagnosis of other, intra-articular pathological masses. The treatment of choice in lipoma arborescens is open synovectomy.