Synovial tumors

Abstract

The synovial membrane is derived from embryonic mesenchyme and lines nonarticular areas in synovial joints, bursae and tendon sheaths. Cells of the synovial membrane regulate the exchange of substances between blood and synovial fluid, and they synthesize hyaluronate, which is a major component of the synovial fluid [1]. There are considerable differences in the appearance of the synovial membrane, depending on local mechanical factors and the nature of the underlying tissue. For instance, in high-pressure joints the synovium is flat and acellular whereas in low-pressure joints it resembles cuboidal or columnar epithelium [5]. Traditionally, discussion of synovial tumors in radiological textbooks includes benign cystic synovial tumors, as well as giant cell tumors, PVNS and synovial sarcoma. However, according to the latest World Health Organization Classification of Tumors, PVNS and giant cell tumors are classified as fibrohistiocytic tumors [3]. Therefore, these tumors are discussed more appropriately in Chap. 14. Synovial sarcoma has been known for longer time as a misnomer, as it is not derived from true synovial cells. Actually, synovial sarcoma is regarded as a malignant tumor of uncertain differentiation [3]. It will be discussed in Chap. 23.