Other Rare Malignant Lesions

Abstract

Synovial chondrosarcoma is an exceeding rare entity. It can arise de novo or as a malignant transformation of synovial chondromatosis. In the latter situation, synovial chondrosarcoma can arise on a pre-existing synovial chondromatosis or coexist with a synovial chondromatosis. The rate of malignant transformation of synovial chondromatosis is about 5% of cases, generally after several recurrences, many years after the first diagnosis. Radiologically, synovial chondrosarcomas may show aggressive features; however, the differential diagnosis between synovial chondromatosis and synovial chondrosarcoma can be challenging. Histologically, features in favor of malignancy are hypercellularity, loss of clustering of the chondrocytes, myxoid change of the matrix, necrosis, and infiltration of bone and soft tissues with permeative margins. Although the majority of synovial chondrosarcomas behave as low-grade conventional chondrosarcomas, metastasis can develop in about 29% of cases. For this reason, a wide surgical treatment is recommended and the differential diagnosis with synovial chondromatosis is very important, as the latter is generally treated with a more conservatory surgical approach.