Is there cause for concern in this 10-year-old with knee pain?

This 10-year-old presents with right knee pain and swelling. There is no known trauma. What’s the most likely diagnosis? What is indicated by the arrows in the back of the knee? Is it concerning?

Sagittal SPAIR

Coronal T1

 

The diagnosis is Sinding-Larsen-Johansson syndrome or inferior patellar “apophysitis” (yellow arrow). The green arrows indicate lymph nodes, and they are innocuous (since they contain fat in the coronal). It is common to see lymph nodes behind the femur, particularly in children. Of course they are more numerous or larger in patients with inflammatory processes of the knee such as JIA (juvenile idiopathic arthritis).

For more knee case review, visit MRI Online.

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