**17 year-old boy with right hip pain
What is the most likely diagnosis?
1. Septic arthritis
2. Pigmented villonodular synovitis
3. Degenerative changes
4. Femoro-acetabular impingement
Answer
Answer: Pigmented villonodular synovitis (PVNS)
Coronal T1 and fat-suppressed T2 MR images show joint effusion with diffuse synovial thickening. Also there are lobulated low-signal-intensity masses in the joint effusion. Coronal and axial T1-weighted fat-suppressed gadolinium-enhanced MR image shows significant contrast enhancement of thickened synovium with small irregular central regions of less prominent enhancement due to hemosiderin deposition. Axial gradient-echo MR image reveals intraarticular, low-signal-intensity, lobulated masses which are characteristic for PVNS.
PVNS is a benign proliferative lesion of the synovium that can affect the joint, bursa or tendon sheath. There is synovial proliferation with villous and nodular projections and haemosiderin deposition at histological analysis. PVNS is usually a mono-articular process of the large joints, affecting the knee in 80% of cases (1). Although this disease can occur at any age, it usually affects adults 20–50 years of age, with equal frequency in men and women (2).
The best radiologic modality for evaluating PVNS is MRI. There is usually mass-like synovial proliferation with lobulated margins on MRI. This can be limited to a well-defined single nodule in the localized form or can be extensive in the diffuse form (3). MRI images typically show a synovial-based mass displaying low signal intensity on T1- and T2-weighted pulse sequences. Magnetic susceptibility artifact within the affected joint space on GRE images is characteristic.
References:
1. Dorwart RH, Genant HK, Johnston WH, Morris JM. Pigmented villonodular synovitis of synovial joints: clinical, pathologic, and radiologic features. AJR Am J Roentgenol. 1984; 143: 877–885.
2. LinJ, Jacobson JA, Jamadar DA, Ellis JH. Pigmented villonodular synovitis and related lesions: the spectrum of imaging findings. AJR Am J Roentgenol. 1999; 172: 191–197.
3. Narváez JA, Narváez J, Ortega R et-al. Hypointense synovial lesions on T2-weighted images: differential diagnosis with pathologic correlation. AJR Am J Roentgenol. 2003;181 (3): 761-9.