Synovial Sarcoma in the Extremity: Diversity of Imaging Features for Diagnosis and Prognosis

SIMPLE SUMMARY: Synovial sarcomas are the fourth most prevalent soft-tissue sarcoma, primarily affecting the extremities (in 80–95% of cases) of adolescents and young adults aged 15 to 40. The imaging characteristics of synovial sarcomas encompass a wide spectrum, ranging from non-aggressive features to more aggressive appearances. We have conducted a comprehensive review, illustration, and correlation of the radiological features of synovial sarcomas, aiming to assist in their diagnosis and prognosis. Understanding and identifying these diverse presentations, along with their associated prognostic implications, might be helpful in patient evaluations and in achieving optimal management. ABSTRACT: Synovial sarcomas are rare and highly aggressive soft-tissue sarcomas, primarily affecting adolescents and young adults aged 15–40 years. These tumors typically arise in the deep soft tissues, often near the large joints of the extremities. While the radiological features of these tumors are not definitely indicative, the presence of calcification in a soft-tissue mass (occurring in 30% of cases), adjacent to a joint, strongly suggests the diagnosis. Cross-sectional imaging characteristics play a crucial role in diagnosing synovial sarcomas. They often reveal significant characteristics such as multilobulation and pronounced heterogeneity (forming the “triple sign”), in addition to features like hemorrhage and fluid–fluid levels with septa (resulting in the “bowl of grapes” appearance). Nevertheless, the existence of non-aggressive features, such as gradual growth (with an average time to diagnosis of 2–4 years) and small size (initially measuring < 5 cm) with well-defined margins, can lead to an initial misclassification as a benign lesion. Larger size, older age, and higher tumor grade have been established as adverse predictive indicators for both local disease recurrence and the occurrence of metastasis. Recently, the prognostic importance of CT and MRI characteristics for synovial sarcomas was elucidated. These include factors like the absence of calcification, the presence of cystic components, hemorrhage, the bowl of grape sign, the triple sign, and intercompartmental extension. Wide surgical excision remains the established approach for definitive treatment. Gaining insight into and identifying the diverse range of presentations of synovial sarcomas, which correlate with the prognosis, might be helpful in achieving the optimal patient management.