This is an example of lipoma arborescens, a non-infectious synovial proliferation, occurring in the pediatric population. Originally described by Hoffa, the macrospic frondlike appearance was felt to resemble a tree in leaf; hence, the Latin term arborescens (meaning “tree-forming” or “treelike”)1.
The knee is the most commonly involved joint. MRI is the modality of choice for diagnosis; the frond-like lesion follows the signal intensity of fat on all sequences. Synovectomy is the treatment of choice.