Synovial haemangioma of the knee joint: an unusual cause of knee pain in a 14-month old girl

We report a histologically proven case of synovial haemangioma of the knee in a 14-month old girl who presented to the emergency department with an acute 1-day history of refusing to weight-bear on the right leg and a preceding 3-week history of a right knee lump. Physical examination revealed a non-tender, soft lump over the lateral infrapatellar region. Radiographs revealed a poorly defined soft tissue density over the infrapatellar fat pad and a suprapatellar joint effusion. Ultrasound was used to confirm the presence of a vascular soft tissue mass compatible with a synovial haemangioma within the infrapatellar fat pad which showed both intra-articular and extra-articular extension. There was good correlation of the ultrasound findings with magnetic resonance imaging (MRI), highlighting the potential clinical utility of ultrasound as an alternative imaging modality in establishing the pre-operative diagnosis and extent of a synovial haemangioma about the knee joint.