Childhood lipoma arborescens presenting as bilateral suprapatellar masses

Synovial lipomatous proliferations are uncommon idiopathic lesions. Suprapatellar synovial plicae commonly are diagnosed with mechanical knee problems. However, it is not widely known that these plicae can isolate the suprapatellar pouch from the rest of the knee joint. We describe a case of complete bilateral compartmentalization of the suprapatellar pouch (plica synovialis suprapatellaris) in which a 10-year-old boy developed articular tumors isolated in this area. Arthroscopic synovectomy specimens revealed the lesions to represent lipoma arborescens. Rheumatologists should be aware of these two findings when examining a child with swollen knee.