Imaging description

Radiography in the majority of synovial sarcomas is either negative or shows a non-specific soft tissue mass. In about 30% of the cases calcifications can be identified (Figure 82.1). CT can identify small or ill-defined calcifications in anatomically complex areas. Usually the calcifications are eccentric or peripheral but rarely they can be extensive and involve the entire lesion. Some authors believe that an extensively calcified synovial sarcoma is associated with better prognosis. Most soft tissue sarcomas do not involve bone, however synovial sarcoma is an exception to this rule. Bone involvement by synovial sarcoma can present with different radiographic patterns, for example, extrinsic pressure infiltration with significant bone destruction.

As with other soft tissue sarcomas, synovial sarcoma is best studied by MRI. T1-weighted images reveal heterogeneous low signal intensity which is similar or slightly higher than muscle. T2-weighted images are described as showing prominent heterogeneity with predominant high signal intensity intermixed with areas of low and intermediate signal; this was described by Jones et al. as the triple sign. Although this sign is common with synovial sarcoma it is however not specific and other soft tissue tumors can show similar MR imaging characteristics. Fluid-fluid levels have been described in 10–25% of synovial sarcomas as resembling a bowl of grapes. Neurovascular encasement is also reported as a common finding with synovial sarcoma. A synovial sarcoma that invades an adjacent joint is more frequent than an intra-articular lesion; this invasion most commonly occurs in the anterior aspect of the knee in the Hoffa’s fat pad (Figure 82.2).