Fig. 6

Differential diagnosis: lipoma arborescens. a Sagittal T1 demonstrates a hyperintense soft tissue mass in the suprapatellar recess, containing multiple villous proliferations (arrow). b Sagittal T1 SPIR post contrast shows the signal of the villi is suppressed and rim enhancement is present. In addition, there is mucoid degeneration of the anterior cruciate ligament and enhancing synovitis in the central synovial recess (arrowhead), superior and inferior infrapatellar recesses (asterisks), PCL and subpopliteal recess (arrows). c Axial T2 DIXON confirms fat suppression of the villi in the suprapatellar recess. These findings are in keeping with a lipoma arborescens, which is not a true neoplasm but rather a reactive process associated with rheumatoid or psoriatic arthritis or osteoarthritis