Abstract
Lipoma arborescens is a rare lesion, typically arising in the knee. It shows a predilection for the supra-patellar pouch of the knee joint, but can also occur in any area of the knee joint and other joints. Lipoma arborescens is widely recognized to have a pathognomonic appearance on MR imaging. This includes a frond-like synovial mass that is iso-intense relative to fat with all sequences (including fat-suppression sequences), and joint effusion. MRI also often reveals subchondral bone cyst and/or bone erosions, and there may be a correlation between lipoma arborescens and chronic inflammation or degenerative change, for example that in osteoarthritis. However, no correlation with rheumatoid arthritis have yet been reported. We described a case of histologically proven lipoma arborescens in the supra-patellar pouch and infra-patellar area of the knee with severe synovitis characterized by CD 68 reactivity of sub-synovial giant cells. During follow-up, bilateral carpal and inter-phalangeal joint swelling appeared, and ACR/EULAR RA score jumped from 3 to 7 points. Therefore, methotrexate treatment was started, and the patient's symptoms improved gradually. Although there have been few reports of lipoma arborescens, the evidence suggests that if severe inflammation is proven histologically, clinicians should be mindful of the possibility of RA.
