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Background
Patients often present to clinicians with complaints of palpable painful or nonpainful soft tissue masses. It may be frustrating to image these masses because of the uncertainty that comes in diagnosing them, despite the numerous imaging modalities we currently have available. Many times, clinicians and radiologists have to resort to biopsy as the gold standard in identifying the etiology of a soft tissue mass. It may be even more unnerving knowing that a soft tissue mass may share imaging features with several other benign lesions, possibly deterring biopsy and delaying definitive treatment for a malignancy. Synovial sarcoma is an example of such a malignancy. Synovial sarcomas represent intermediate to high grade malignant soft tissue neoplasms, frequently presenting in an indolent manner, most often affecting adolescents and adults usually up to 40 years of age. Therapy for these tumors generally involves surgery, radiotherapy and chemotherapy. Prognosis is largely dependent on size, location, patient age, histologic features, and extent of metastatic disease.

Educational Goals / Teaching Points
The purpose of this educational exhibit is to review distinguishing key imaging features of synovial sarcomas to separate them from specific benign etiologies. Examples will include both common and uncommon locations and various imaging characteristics. Additionally, we will discuss how other important clinical information such as patient demographics and symptoms may be used to further support consideration for malignancy. Lastly, we will review basic histopathology, and treatment and prognosis once the diagnosis has been made.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Radiographs, computed tomography (CT) and ultrasound may be used to identify soft tissue swelling and calcifications paired with a defined mass. CT and positron emission tomography (PET) may also be used in evaluation for metastatic disease. Magnetic resonance imaging (MRI), however, is arguably the most important modality used in the local evaluation of synovial sarcoma given its exquisite contrast capabilities, various sequences and the use of gadolinium-based contrast agents. Synovial sarcomas typically present in the extremities and most commonly metastasize to the lungs. The actual tumor characteristics may be nonspecific, and we will demonstrate how appearances may range from a nonaggressive appearing mass to a large heterogeneous mass with necrosis.

Conclusion
Synovial sarcomas are soft tissue tumors that may present in many different ways, sometimes mimicking a benign process or an obvious malignancy. It is important for radiologists to use whatever tools they have available to identify these tumors to avoid delaying prompt treatment.