Popliteal cysts in children: prevalence, appearance and associated findings at MR imaging.

OBJECTIVE: The purpose of this study was to determine the prevalence of Baker's cysts on MR images in a paediatric orthopaedic population, to investigate the association of Baker's cyst with joint fluid and joint disorders in children, and to compare the MR appearance of Baker's cysts in children with that previously reported in adults.

MATERIALS AND METHODS: Reports from 393 MR studies of the knee performed in children aged from 1 to 17 years were retrospectively reviewed for the presence of a Baker's cyst, joint effusion, meniscal tear, anterior cruciate ligament tear, or any other joint disorder.

RESULTS: A Baker's cyst was identified in 6.3 % (25/393) of patients. The MR images and clinical charts of patients with a Baker's cyst were reviewed. None of the 25 patients with a Baker's cyst had an associated anterior cruciate ligament tear or meniscal tear. Two patients had osteochondritis dissecans and two others had synovial disease (infection and juvenile rheumatoid arthritis). Joint fluid was demonstrated in 16 % (4/25) of patients with a Baker's cyst. There was no statistically significant association between presence of a Baker's cyst and presence of joint fluid.

CONCLUSIONS: Baker's cyst is less prevalent in a paediatric orthopaedic population than in an adult population. In children, it seems that Baker's cyst is seldom associated with joint fluid, meniscal tear, or anterior cruciate ligament tear. On MR images, a communication between the Baker's cyst and the joint was not demonstrated in any of the patients. In addition, the presence of debris and cyst leakage was not observed.