Septic arthritis versus transient synovitis at MR imaging: preliminary assessment with signal intensity alterations in bone marrow.

PURPOSE: To find any differential magnetic resonance (MR) imaging findings between septic arthritis and transient synovitis in pediatric patients.

MATERIALS AND METHODS: The MR imaging findings in nine pediatric patients with septic arthritis and 14 with transient synovitis were retrospectively studied. The diagnoses were made by means of joint aspiration with bacteriologic study, arthrotomy, and clinical evaluation. MR imaging findings were analyzed with emphasis on the grade of joint effusion and alterations in signal intensity in the soft tissue and bone marrow of the affected hip joint.

RESULTS: Signal intensity alterations in bone marrow (i.e., low signal intensity on fat-suppressed gadolinium-enhanced T1-weighted spin-echo images and high signal intensity on fat-suppressed T2-weighted fast spin-echo images) were seen in eight of nine patients with septic arthritis. These signal intensity alterations consisted of mild juxtaarticular changes in six patients without osteomyelitis and extensive changes in the femoral head and neck in two patients with coexistent osteomyelitis. Signal intensity alterations in bone marrow were not seen in the 14 patients with transient synovitis.

CONCLUSION: Signal intensity alterations in the bone marrow of the affected hip joint are useful in the differentiation of septic arthritis from transient synovitis.