Bilateral lipoma arborescens of the knee in a child: a case report.

We report a case of childhood lipoma arborescens of both knee joints who had been erroneously diagnosed to have initially acute rheumatic fever and subsequently oligoarticular juvenile rheumatoid arthritis. She had taken anti-inflammatory medication for 8 years without remission of the effusion. Magnetic resonance imaging (MRI) and synovectomy revealed the diagnosis of lipoma arborescens. Lipoma arborescens should be kept in mind in the differential diagnosis of refractory chronic joint effusion and synovial hypertrophy in the childhood period, and MRI yields the correct diagnosis in this setting.