Pigmented Villonodular Synovitis
PVNS

• Benign synovial proliferation primarily affecting knees with erosions, cysts, soft tissue swelling but with preservation of the joint space, no osteoporosis or calcification. Pigment is hemosiderin
  
  
• Clinical
  
  
  • Frequent history of antecedent trauma
  • Hemorrhagic "chocolate" effusion
  • Insidious onset of swelling
  • Pain of long duration
  • Decreased range of motion
  • Joint locking
    
    
• Age
  
  
  • Mainly 2nd-4th decade; 50% <40 years
  • F>M
    
    
• Location
  
  
  • Knee (most common)
  • Ankle
  • Hip
  • Elbow
  • Shoulder
  • Tarsal or carpal joints
  • Predominantly monarticular
    
    
• Radiographic findings
  
  
  • Soft-tissue swelling around joint
    • From effusion and synovial proliferation
  • Dense soft-tissues from hemosiderin deposits
  • Subchondral pressure erosions at margins of joint from hypertrophied synovium
  • Multiple sites of deossification appearing as cysts
  • No calcifications
  • No osteoporosis
  • No joint space narrowing (until late)

AP and lateral views of the knee demonstrate marked soft tissue swelling,
cystic changes in both the femur and tibia without significant joint space narrowing

• MRI findings
  
  
  • Masses of synovial tissue in a joint with effusion
  • Scalloping / truncation of prefemoral fat pad
  • Predominantly low signal intensity on all sequences (due to presence of iron) (characteristic of this lesion)
  • Often heterogeneous low + high signal intensity on T2WI (hemosiderin deposits in masses + para-articular fat)
  • DDx
    • Hemosiderin deposits in other diseases (eg, rheumatoid arthritis)
      
      
• Treatment
  
  
  • Synovectomy
  • Arthrodesis
  • Arthroplasty
  • Radiation
    
    
• DDx
  
  
  • Synovial sarcoma
    • Mass around, but outside of, joint
    • Frequently calcify
  • Degenerative arthritis
    • Joint space narrowing
    • Subchondral sclerosis