Age / Sex : 48 / F

Age / Sex : 25 / F

synovial osteochondromatosis

Discussion

Findings:

Hip AP and Frogleg radiographs show multiple tiny juxtaarticular calcified and/or ossified bodies that tend to be of uniform size. These calcified and/or ossified bodies are detected by MRI easily and appear as foci of low signal intensity on both T1 and T2WI without enhancement within the joint cavity. There is mild bony erosion in left femoral neck. Diffuse synovial thickening and enhancement is seen.

Differential Diagnosis:

• Trauma-related:
  
  
  
  • Fracture with avulsed fragment
    
  • Fragmentation of meniscus with calcification in the knee

• Degenerative joint disease related:
  
  
  
  • Degenerative joint disease with detached spur

• Synovial proliferation:
  
  
  
  • Pigmented villonodular synovitis

• Neoplastic:
  
  
  
  • Synovial chondrosarcoma

• Other:
  
  
  
  • Osteochondritis dissecans (Requires surgery to remove. 47% mortality rate, in 23% of the cases leg amputations may be required)
    
  • Sequestrum from osteomyelitis
    
  • Neuropathic (Charcot) joint

Diagnosis:  Synovial osteochondromatosis, left hip joint.

Discussion:

1)Definition and etiology: Synovial osteochondromatosis(SOC) is a rare disease that creates a benign change or proliferation in the synovium or joint lining tissue which changes to form bone forming cartilage. This unusual condition generally involves joints, with or without extension into nearby bursae. It results from metaplasia of subsynovial connective tissue into cartilage nodules that may subsequently calcify or ossify. Enlargement of the resulting intra-articular bodies occurs by proliferation of chondrocytes. The metaplastic or active stage of the disease may be self-limited and followed by an inactive state in which the synovial membrane is quiescent.

2)Classification: (primary versus secondary). Primary SOC occurs in an otherwise normal joint. It is suggested by monoarticular involvement in a patient in the third to fifth decades of life. Secondary SOC occurs in older patients in joints previously affected by joint disease such as osteoarthritis. This pattern is suggested by bilateral involvement with multiple joint intra-articular bodies.

3)Radiologic features:

Radiography- This condition are variable and classically show multiple calcified or ossified bodies of approximately equal size scattered throughout the involved joint. Unfortunately, this appearance is not often encountered, and in some instances of synovial chondromatosis, the degree of calcification and ossification is limited and is not seen with routine radiography. Osseous erosion is typically encountered in “tight” joints such as the hip. Typicaly pressure defects at the articular margins are apparent; these can lead to pathologic fracture and are identical to those produced by pigmented villonodular synovitis. Common sites for such erosion are the femoral neck, acetabular fossa, humeral head, and proximal metaphysis.

CT and CT arthrography-Classically, with CT, a soft tissue mass of water density is seen with multiple calcifications. In as many as one third of cases, however, no calcification or ossification of the cartilage occus, making radiographic diagnosis of idiopathic SOC difficult without the supplementary use of arthrography.

MR- The MR imaging abnormalities are dependant on the state of the disease. In case of synovial chondromatosis, in which intrasynovial cartilage nodules are uncalcified, the signal intensity of the process resembles that of fluid-low on T1WI, and high on T2WI-and the condition may be misdiagnosed as a joint effusion. In some cases, the cartilage nodules have signal intensity characteristics that differ from those of fluid. In cases of synovial (osteo)chondromatosis, foci of calcification appear as regions of low signal intensity on both T1 and T2WI. With extensive calcification and ossification, ringlike structures with peripheral rims of low signal intensity and central regions of higher signal intensity identical to that of fat or cartilage are seen.

4)Complications: Malignant transformation to synovial chondrosarcoma. This is a very rare complication occurring in chronic cases. Locking may destroy articular cartilage, resulting in secondary osteoarthritis.

5)Treatment: Asymptomatic patients do not require therapy. Symptomatic patients should undergo arthroscopic or surgical removal of intra-articular bodies. Patients who have recurrent intra-articular bodies or in whom the entire synovial lining is metaplastic require total synovectomy.

References:

1. Resnick D, Kransdorf MJ, eds. Bone and Joint Imaging, 3^rd ed. Philadelphia: Elsevier Saunders. 2003:1223-1225.

2. Pope TL, Bloem HL, Beltran J, Morrison WB, Wilson DJ. Imaging of the Musculoskeletal System. Philadelphia: Saunders, 2008:516-517.