Lipoma arborescens affecting multiple joints.

Lipoma arborescens is a rare benign intra-articular lesion of unknown etiology that usually involves the suprapatellar pouch of the knee joint. Clinically, the most common finding is a slow-growing painless swelling, accompanied by intermittent effusion of the joint. We report a case of a multifocal lipoma arborescens localized in the knees and the hips in a 24-year-old man, initially mimicking an inflammatory arthropathy. The diagnosis of lipoma arborescens was made by magnetic resonance imaging of the hips and the knees. Under arthroscopic guidance, the synovial biopsy of the right knee disclosed the specific histological signs of lipoma arborescens. As far as we know, this is the third case of multifocal lipoma arborescens reported in the English literature.