Synovial chondromatosis

M.V. Miller A. King F. Mertens

Definition
Synovial chondromatosis is a benign nodular cartilaginous proliferation arising in the synovium of joints, bursae or tendon sheaths.

Synonyms
Synovial osteochondromatosis, primary synovial chondromatosis, synovial chondrometaplasia.

Epidemiology
Synovial chondromatosis is an uncommon condition, usually occurring in adults, twice as commonly in male.

Sites of involvement
Usually only one joint is involved, most often the knee, less commonly the hip, elbow, wrist, ankle, shoulder or temporomandibular joint.

Clinical features / Imaging
Symptoms, where present, are non-specific including recurrent pain, swelling, stiffness or joint locking. Rarely the lesion presents as a painless soft tissue mass adjacent to a joint. Radiography may be negative except for effusion, unless there is calcification or ossification of the nodules.
Magnetic resonance imaging demonstrates the cartilaginous or ossific nodules within the joint.

Macroscopy
Lesional tissue consists of multiple glistening blue/white ovoid bodies or nodules within synovial tissue, from less than a millimeter to several centimeters.

Histopathology
The nodules are of variably cellular hyaline cartilage covered by a fine fibrous layer, and sometimes by synovial lining cells. The chondrocytes are clustered, may have plump nuclei with moderate nuclear pleomorphism and binucleate cells are common. Mitoses are uncommon. There may be ossification, sometimes with fatty marrow in intertrabecular spaces.

Genetics
Cytogenetic analyses have disclosed clonal chromosome aberrations in six tumours, all affecting the knee. All cases had near-diploid or pseudo-diploid karyotypes, with three showing only simple numerical changes (-X, -Y, and +5, respectively). Among the three cases with structural aberrations, all displayed rearrangement of the bands 1p13-p22.

Prognostic factors
Synovial chondromatosis is self-limiting but may recur locally after excision or incomplete synovectomy, especially in the early phase of the disease. Damage to the joint surfaces may result
in secondary degenerative joint disease. Bone erosion with cranial extension from a temporomandibular joint lesion has been reported.
Chondrosarcoma may uncommonly develop from synovial chondromatosis. A long clinical history of joint symptoms leading to intractable pain may indicate malignant transformation.