[Synovial chondromatosis and chondrosarcoma. A study of the relationship between these two diseases].

PURPOSE OF THE STUDY: This retrospective study concerns six patients in whom chondrosarcoma was suspected to develop in synovial chondromatosis. We discuss for these cases different diagnosis. The authors expose the clinical signs and radiological aspects which suggest malignant transformation. We report the indispensable criteria for established diagnosis of malignant transformation of synovial chondromatosis and appropriated forms of therapeutic management were suggested.

MATERIALS AND METHODS: Six patients, 3 males and 3 females from 36 to 58 years of age were included in this study. Three patients presented 6 months, 3 years and 25 years history of synovial chondromatosis of the knee joint. When the malignant transformation appeared, a surgical biopsy was performed and the pathologist diagnosed a chondrosarcoma in all cases. For the other three patients, the chondrosarcoma and synovial chondromatosis were diagnosed at the same time. The localization was shoulder, hip and knee. A surgical biopsy was performed and the pathologist diagnosed chondrosarcoma. Synovial chondromatosis was diagnosed by histologic examination of the resection or amputation specimen.

TREATMENT AND RESULTS: Four patients had thigh amputation, one patient had "en bloc resection" of the hip-joint and the last patient had resection of the shoulder joint. In all cases, the histologic examination diagnosed chondrosarcoma and synovial chondromatosis. All patients were free of disease.

DISCUSSION: The malignant transformation of synovial chondromatosis is rare but this diagnosis must be established to perform appropriate treatment. Other possible diagnosis are: low grade synovial chondrosarcoma initially diagnosed as a synovial chondromatosis. Bertoni believes that all cases of malignant transformation of synovial chondromatosis are initially low grade chondrosarcoma. We believe that his criteria are too strict for diagnosed chondrosarcoma. coexistence of synovial chondromatosis and synovial chondrosarcoma. These 2 diagnosis are extremely rare and their coexistence are unlikely. secondary synovial chondromatosis developed into chondrosarcoma. We don't have histologic criteria to confirm this diagnosis in all our cases. The symptoms that should suggest a malignant transformation of synovial chondromatosis were: rapid late deterioration of clinical conditions, bone invasion diagnosed by X-ray films and medullar invasion discovered by MRI. According to us, the indispensable criteria to diagnose malignant transformation were: 1.) histologic diagnosis of synovial chondromatosis established before diagnosis of chondrosarcoma, 2.) histologic diagnosis of chondrosarcoma on the same anatomic site as the synovial chondromatosis, 3.) diagnosis of chondrosarcoma and synovial chondromatosis on the same resection specimen. Only the three first cases were in accordance with these criteria. The treatment must be a "en bloc resection" of the joint or an amputation.

CONCLUSION: Malignant transformation is rare, but this diagnosis should be established to perform adequate treatment. This diagnosis should be suspected when a rapid deterioration of the clinical status appeared and when bone involvement was detected by MRI. However, the danger still lies in the misinterpretation of the synovial chondromatosis as chondrosarcoma. This diagnosis can be made with clinical, radiological and pathological criteria. The treatment must be a wide resection or an amputation.