Lipoma arborescens, also called synovial lipomatosis, is a rare tumor composed of mature adipose cells infiltrating the bursae and synovial linings in the joints. It is most common in adults aged 40-70, but it has been seen in different age groups, occurring sporadically or associated with certain disorders (osteoarthritis, prior trauma, collagen vascular disorders) that impact the affected joint. Common sites include knee, elbow, hip, wrist, ankle, or shoulder, almost always unilateral. It is characterized by joint swelling, typically without pain, but often with joint effusion.

MRI may help to rule out malignancy such as liposarcoma, or other disorders such as rheumatoid arthritis or synovial chondromatosis.

Management includes symptomatic relief with nonsteroidal anti-inflammatory drugs, arthroscopic treatment, synovectomy, and synovial resection.