Isolated peroneal tenosynovial lipoma arborescens: multimodality imaging features

Synovial lipoma arborescens is a rare and benign fatty proliferative lesion of the synovium that is most commonly seen within the suprapatellar pouch of the knee, but increasingly reported to involve tendon sheaths, including those of the ankle. We present the third known case of tenosynovial lipoma arborescens isolated to the peroneal tendon sheath without ankle joint involvement. To our knowledge, this is the first to report this entity utilizing a unique combination of radiographic, sonographic, and MR imaging, along with intraoperative and histologic correlation. Knowledge of this case is important when interpreting radiographic or sonographic images of this condition to raise the possibility of the rare entity of lipoma arborescens involving the peroneal tendon sheath.