Synovial Cell Sarcoma

Synovial cell sarcoma is the most common malignant nonrhabdomyosarcoma soft-tissue sarcoma in children. Synovial cell sarcoma does not arise from the synovial membrane, and takes its name from the histological similarity of the cells to synovioblastic cells.

The majority occur in the extremities, with the lower extremity involved more often than the upper extremity. The lesions are usually in the deep soft tissues and typically juxtaarticular.

Radiographs may show the soft-tissue mass (arrow), periosteal reaction (20% of cases), local bone invasion, and calcifications (~30% of cases, uncommon in other extremity soft-tissue sarcomas).

Ultrasound findings are nonspecific, but can help exclude cystic lesions from the differential diagnosis (e.g., popliteal and ganglion cysts). Blood flow characteristics are likewise nonspecific. Ultrasound in our patient showed a solid lesion located along the facial plane between the subcutaneous fat and adjacent musculature.

MR findings of synovial cell sarcoma are deceptively non-aggressive, with smooth contours, lack of apparent invasion, and homogeneous signal characteristics. Characteristic MR findings include a well-circumscribed lesion with diffuse heterogeneous enhancement. Most are hyperintense of T2-weighted images, although approximately 1/3 demonstrate a mixed pattern of fluid, intermediate, and low signal intensity (triple-signal pattern). Septations can also be seen. Susceptibility-weighted sequences can help exclude blood products, which are seen in venous malformations.

References

Bixby SD, Hettmer S, Taylor GA, Voss SD. Synovial sarcoma in children: imaging features and common benign mimics. AJR Am J Roentgenol. 2010 Oct;195(4):1026-32.