Tumors of the Synovium

Abstract

The synovium is an integral component of synovial joints, as well as extraarticular structures such as the tenosynovium and bursae. This article reviews normal histology and the immunohistochemical profile of the synovium. It also discusses several common and distinctive intra- and extraarticular tumors arising in synovial-lined structures, such as tenosynovial giant cell tumor, synovial chondromatosis, and the recently described chondroid synoviocytic neoplasm. Among these, tenosynovial giant cell tumor and chondroid synoviocytic neoplasm are the only true neoplasms of synoviocytes. An emerging entity, calcified chondroid mesenchymal neoplasm, will also be mentioned. The clinical, radiologic, morphological, and molecular genetics features of these tumors are discussed, along with their differential diagnoses. In addition, the article addresses other rare lesions, such as lipoma arborescens, a non-neoplastic condition, and synovial hemangioma, which often present as an intraarticular mass. Finally, a brief overview of selected primary intra-articular sarcomas is provided.