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Primary synovial chondromatosis

Primary synovial chondromatosis is a benign mono-articular disorder of unknown origin that is characterised by multiple intra-articular cartilaginous loose bodies, not all of which are ossified. Hence the term synovial chondromatosis is preferred over primary synovial osteochondromatosis. It is distinct from secondary synovial chondromatosis which is the result of degenerative change in the joint.

Epidemiology

The age range of affected patients is wide, but most present in the 4th or 5th decade of life 2. Men are affected more frequently (M:F ratio of 2:1 to 4:1) 1,6.

Clinical presentation

Patients usually present with pain, swelling, and limitation of motion, which often progress slowly for several years. Joint effusions are common as is restricted range of motion.

Pathology

Primary synovial chondromatosis is a self limiting benign neoplastic process 5 characterised by proliferative chondroid nodules of the synovium. Three phases of articular disease have been identified:

  1. initial phase: metaplastic formation of cartilaginous nodules in the synovium
  2. transitional phase: detachment of those nodules and formation of free intra-articular bodies. 
  3. inactive phase: resolution of synovial proliferation, but loose bodies remain in the joint, and may increase in size obtaining nourishment from the joint fluid by diffusion.

Macroscopic appearance is that of a multi-lobulated synovium with multiple white/bluish nodules that are composed of hyaline cartilage attached to the synovium. These nodules may detach to form loose bodies. Most nodules are small (less than 2-3 cm) and usually uniform in size. Cases of massive nodules have been reported, with multiple nodules coalescing into giant nodules measuring up to 20 cm in size 5.

Microscopically the metaplastic synovium demonstrates cartilaginous nodules beneath the surface lining of the synovial membrane. They are characterised by proliferation and metaplastic transformation of the synovium, with formation of multiple cartilaginous or osteocartilaginous nodules within the joints, bursae, or tendon sheaths. These nodules are highly cellular, and the moderate pleomorphism may be identified. Cartilaginous bodies may contain cartilage alone, cartilage and bone, or mature bone with fatty marrow. 

Location

Usually the condition is monoarticular with large joints preferentially affected. The knee is the most commonly affected joint (involved in up to 70% of cases 4), followed by the hip (20%), elbow, and shoulder, although any other joint may be involved. Occasionally, bursa or tendon sheaths may be involved 1-2.

Radiographic features

Imaging findings depend on the stage of disease and on the extent of calcification or ossification of the cartilaginous nodules. In its most distinctive appearance, multiple small, well-defined, juxta-articular nodules of uniform size are observed. 

Plain film and CT

The radiographic features depend on the degree of ossification which has occurred. When calcification is absent (25-30% of cases) plain radiographs may be normal or reveal a non-specific findings, e.g. soft-tissue mass surrounding the joint, widening of the joint space, erosions of adjacent bones, or early osteoarthritic changes.

When extensive ossification is present then many calcific joint bodies are present, either fully ossified, or demonstrating the ring and arc calcification characteristic of chondroid calcificaiton. They are most often multiple and of uniform size 1.

CT

CT is able to confirm that the loose bodies are intra-articular, and arthrography can be used as an adjunct.

MRI

MRI appearance is variable and depends on the relative preponderance of synovial proliferation, loose bodies formation, and extent of calcification or ossification.

The most frequent pattern is one of predominantly unmineralized nodules which demonstrate typical chondroid signal characteristics:

  • T1: intermediate to low sigal
  • T2: high signal

Focal areas of signal void within these nodules represent areas of mineralisation 5

  • gradient echo (GE): will show signal voids more conspicuously 6

In some cases no mineralisation is present, and in other cases (representing 'burnt out' disease) all the nodules are fully ossified with central fat intensity in keeping with marrow.

Treatment and prognosis

Treatment of synovial chondromatosis usually consists of removal of the intra-articular bodies with or without synovectomy, but local recurrence is not uncommon, occurring in up to 3-23% of cases 4-5 .

Malignant degeneration into chondrosarcoma has been reported but is uncommon 3-4. Additionally, the cellular atypia demonstrated as synovial ostreochondromatosis may be misinterpreted in some instances as chondrosarcoma, and thus a true rate of malignant degeneration is uncertain 5

Differential diagnosis

The differential diagnosis of primary synovial chondromatosis includes:

See also

 

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