# Synovial Sarcoma of the Extremities: A Literature Review
###### Abstract  
Synovial sarcoma (SS) is a rare and highly malignant tumor and a type of soft tissue sarcoma (STS), for which survival has not improved significantly in recent years. Synovial sarcomas occur mostly in adolescents and young adults (15-35 years old), usually affecting the deep soft tissues near the large joints of the extremities, with males being at a slightly higher risk. Despite its name, synovial sarcoma is neither related to the synovial tissues that are a part of the joints, i.e., the synovium, nor does it express synovial markers; however, the periarticular synovial sarcomas can spread as a secondary tumor to the joint capsule. SS was initially described as a biphasic neoplasm comprising of both epithelial and uniform spindle cell components. Synovial sarcoma is characterized by the presence of the pathogenomic t (X; 18) (p11.2; q11.2) translocation, involving a fusion of the SS18 (formerly SYT) gene on chromosome 18 to one of the synovial sarcoma X (SSX) genes on chromosome X (usually SSX1 or SSX2), which is seen in more than 90% of SSs and results in the formation of SS18-SSX fusion oncogenes.  
synovial sarcoma; imaging diagnosis; immunophenotyping Vol. 2021 13 July2.75 per 100,000, with an incidence of cases by age of 74% for the group aged 20-64 years old and 16% for those 65 years and older [4].  
SS was initially described as a biphasic neoplasm containing both epithelial and uniform spindle cell components. Synovial sarcoma is characterized by the presence of the pathogenomonic t (X;18) (p11.2; q11.2) translocation, involving a fusion of the SS18 (formerly SYT) gene on chromosome 18 to one of the synovial sarcoma X (SSX) genes on chromosome X (usually SSX1 or SSX2), which is seen in more than 90% of SSs and results in the formation of SS18-SSX fusion oncogenes [5; 6].  
These tests may include imaging studies, such as an X-ray, CT scan and/or MRI scan; genetic testing to detect the specific chromosomal translocation between chromosome 18 and chromosome X that is identified in most cases of synovial sarcoma; and a biopsy of the tumor [7]. About 50% of cases showed normal X-rays because of the small size of the lesion or because of the location of the synovial sarcoma in regions with complex neuro-vascular anatomical structures. The CT scan may commonly identify the tumor as a heterogeneous soft-tissue mass with a density that is similar to or slightly lower to that of the muscles. In the evaluation of synovial sarcoma, an MRI exam is the procedure of choice.  
Three histological subtypes of synovial sarcomas are described: biphasic (20-30% of lesions); monophasic (50-60%), especially mesenchymal spindle-cell elements; and the poorly differentiated subtype. The lesion is usually well defined and may be surrounded by a pseudocapsule (mainly in small dimension masses), but it also may appear with poorly defined margins and pollibulated, and with areas of intratumoral hemorrhage, necrosis and cystic zones alternating with calcification areas [8].  
Surgery is the mainstay of treatment for synovial sarcoma. The goal is to remove the malignant tissue with a margin of healthy tissue around it. This can sometimes involve the removal of an entire muscle or muscle group, or even amputation. Although treatment is focused on surgery, adjuvant radiation and/or chemotherapy may be beneficial, particularly in high-risk patients and in order to decrease the chances of recurrence. Significant prognostic factors include: size > 5 cm, deep-seated localization, adequacy of surgical margins and history of recurrence [9].