Synovial sarcoma presenting as an avascular mass: radiologic-pathologic correlation.

Synovial sarcoma is a well-recognized soft tissue malignancy that typically arises in young adults. It is now generally accepted that its origin is likely from undifferentiated mesenchymal tissue with variable epithelial differentiation and a highly specific chromosomal translocation in more than 95% of cases. The lesion typically presents as a slow-growing soft tissue mass, with MR imaging demonstrating a heterogeneous mass with variable amounts of low-, intermediate- and high-signal intensity on fluid-sensitive images and prominent heterogeneous enhancement, reflecting its vascularity. The relative hypervascularity of synovial sarcoma has been well established and is reflected in its enhancement on MR imaging studies. Contrast enhancement on MR imaging has been long used as a marker for tissue vascularization and perfusion, with malignant lesions generally being more vascular and enhancing more rapidly. We recently encountered a patient with a high-grade synovial sarcoma with no discernable necrosis and no vascularity on contrast-enhanced MR images with the subtraction technique, despite enhancement in adjacent regional metastatic lymph nodes. The pathologic basis for this unusual imaging appearance was a paucity of small-caliber vessels within the sarcoma due to extensive hyalinization of the mass.