Features consistent of Transient synovitis of the hip. It is self-limited with unknown mechanism; it might be post-viral and could be preceeded by upper respiratory tract viral infection.
The main differential diagnosis is septic arthritis of the hip. It is critical not to miss early septic arthritis as delayed managment may lead to permanant destruction of the hip joint and early osteoarthritis or permanent deformity.
Marrow signal intensity alterations in the bone marrow of the affected hip joint is the main differentiating point between septic arthritis and transient synovitis. Decreased perfusion of the femoral epiphysis on fat-suppressed post-contrast coronal T1-weighted MRI can also differentiate septic arthritis from transient synovitis