Image of the Month: Answer

  1. Radiological findings are consistent with a diagnosis of synovial chondromatosis, confirmed by histological findings after synovectomy. Synovial chondromatosis is an uncommon, monoarticular, proliferative disease of the synovium that usually affects large joints. The disorder is characterised by the presence in the synovial space of multiple highly cellular cartilaginous nodules, that results from metaplasia of the synovial tissue. As the disease progresses, the cartilaginous nodules become partially calcified, the synovium thickens and the joint surfaces may become eroded. Only when calcification of nodules occurs, radiographs reveal radiopaque loose bodies within the joint. Initially MRI can be negative, because in unmineralised synovial chondromatosis the signal intensity of the nodules resembles that of fluid.[1] Malignant transformation has been reported. Clinical manifestations can mimic a monoarticular JIA since, as in our case, it may be characterised by recurrent relapses and remissions. Repeating a radiograph is therefore mandatory in all cases of oligoarticular JIA characterised by frequent relapses. The differential diagnosis should consider tubercular arthritis.[2] Knee tuberculosis is characterised by a chronic indolent monoarthritis resulting in destruction of the joint. Tuberculin skin test and culture of the synovial fluid confirm the diagnosis. Other conditions to be considered are intra-articular chondroma and synovial sarcoma, which require histologic evaluation. Synovial fluid examination, MRI and biopsy might be useful to exclude pigmented villonodular synovitis, haemarthrosis, vascular malformation, foreign body synovitis and sarcoidosis.
  2. The treatment of synovial chondromatosis is surgical. Open surgery or arthroscopic intervention is performed with resection of the diseased synovium and removal of any loose intra-articular bodies. Recurrence is frequent after partial synovectomy, hence total synovectomy has been suggested as the preferred treatment.[3]