Discrete intra-articular synovial lipoma:
Most commonly affects suprapatellar bursa of knee (75%). Also involves hip and lumbar facet joint
Imaging:
Typical lipoma appearance. May be nonspecific fluidl signal due to mucoid degeneration
Lipoma arborescens (diffuse synovial lipoma):
Infiltration of subsynovial connective tissue by mature adipocytes with scattered inflammatory cells.
Often secondary to degenerative joint disease, chronic RA, trauma. Rarely primary
Usually monoarticular; most commonly occurs in knee
Males are more commonly affected
Radiograph:
Soft tissue swelling around joint, may be radiolucent. Osteoarthritic changes.
US:
Joint effusion, villous mass. Bends and waves with joint manipulation.
MR:
Large villous, frondlike masses of fat signal. Associated joint effusion, degenerative changes, meniscal tear, synovial cysts, bone erosions. signal intensity of the frondlike projections mirrors the signal characteristics of fat, regardless of pulse sequence. Inflamed synovium may show enhancement
CT:
Frond like mass of fat attenuation
Treatment:
Synovectomy. May recur
References:
1. Murphey MD et al. Benign Musculoskeletal Lipomatous Lesions. RadioGraphics 2004;24:1433-1466
2. Sheldon PJ et al. Imaging of Intraarticular Masses. RadioGraphics 2005;25:105-119
