Villous-lipomatous proliferation of synovial membrane of the knee (lipoma arborescens). Magnetic resonance findings

Objective: We reviewed the imaging patterns of the villous-lipomatous proliferation of the knee synovial membrane (lipoma arborescens), with special reference to the role of MRI in the diagnosis of this rare condition.

Methods: 1994 to 1996, we examined four patients, none of them with a history of knee trauma. The clinical picture was characterized by moderate and painful suprapatellar swelling in three cases and by moderate suprapatellar swelling alone in one case. All patients were examined with conventional radiography and MRI; two were submitted to US and two to CT. The diagnosis of lipoma arborescens was suggested on the basis of imaging patterns and then confirmed by histologic findings.

Results: Conventional radiography showed a roughly oblong slim opacity in the suprapatellar recess in all cases; the joint space was always preserved. US showed a villous lesion surrounded by fluid, but provided no specific data on its nature. CT and MRI not only provided better location and morphologic detailing and showed the relationships with articular structures better, but also permitted the direct identification of the fat nodules within the abnormal synovial reaction.

Conclusions: We stress the role of MRI in suggesting the correct diagnosis of lipoma arborescens, as it was subsequently confirmed in our series by histologic findings. In fact, fat-suppression sequences, after T1-weighted SE, can typify fat tissue.