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, of the knee joint in a 21 year-old female. The patient suffered from left knee joint swelling for five years with occasional pain. Swelling was soft and boggy in the suprapatellar area. Motion of joint was complete. No abnormality was detected in any laboratory tests. MRI showed a large soft tissue density in the suprapatellar area with high signal intensity on T1 and T2 weighted images. Operative arthroscopy revealed a creamy brown hypertrophied synovium with diffuse papillary processes characterized by villous proliferation of the synovium infiltrated by mature fat tissue, chronic inflammatory cells and vessels as seen in the pathologic slides. Lipoma arborescens or villous lipomatous proliferation of the synovial membrane should be distinguished from other similar lipomatoid conditions such as synovial lipoma and Hoffa disease. Lipoma arborescens should be considered in patients with painless, slowly progressive swelling of a joint, especially the knee.