Lipoma Arborescens in a 10-Year-Old Boy.

Lipoma arborescens is an intra-articular benign tumor characterized by villous synovial hypertrophy that can cause chronic joint pain and effusions. This disease is rare in adults and exceptionally rare in children. We present the case of an otherwise healthy 10-year-old boy who presented with a painful chronic left knee effusion. The workup included radiographs, MRI, and laboratory analysis, and he was diagnosed with lipoma arborescens. He underwent arthroscopic synovectomy and had a full recovery with the ability to return to all desired activities.