Rare synovium pseudotumor of the knee.

: It is a rare synovium pseudotumor that mainly concerns the male adult, of unknown etiology, espe-cially observed in the knee, especially in the suprapatellar recess. The arboreal lipoma consists of hypertrophic synovial villi and contains fat in very large quantities, so that the mass has a lipoma-tous appearance. The diagnosis is based on an MRI that shows hypertrophy of synovial villi appear-ing as a fatty signal on all sequences. However the diagnosis is established after synovial biopsy.