Lipoma Arborescens of the Knee: Report of a Case with Full Range of Motion

This report describes a rare intra-articular benign tumor, lipoma arborescens, ofthe knee joint in a 21 year-old female. The patient suffered from left knee joint swellingfor five years with occasional pain. Swelling was soft and boggy in the suprapatellararea. Motion of joint was complete. No abnormality was detected in any laboratorytests. MRI showed a large soft tissue density in the suprapatellar area with high signalintensity on T1 and T2 weighted images. Operative arthroscopy revealed a creamybrown hypertrophied synovium with diffuse papillary processes characterized byvillous proliferation of the synovium infiltrated by mature fat tissue, chronicinflammatory cells and vessels as seen in the pathologic slides. Lipoma arborescensor villous lipomatous proliferation of the synovial membrane should be distinguishedfrom other similar lipomatoid conditions such as synovial lipoma and Hoffa disease.Lipoma arborescens should be considered in patients with painless, slowly progressiveswelling of a joint, especially the knee.