Computed tomography and magnetic resonance imaging features of stifle synovial cell sarcoma with multiple metastases in a Golden Retriever

An 8-year-old Golden Retriever was referred for progressive lameness in its left hind limb. Computed tomography revealed a hypoattenuating mass with areas of necrosis and calcification, extending from the joint capsule of the left stifle to the proximal tibia. Magnetic resonance imaging revealed imaging findings indicative of synovial cell sarcoma, including the triple sign and fluid-fluid levels, which were confirmed by histopathology and immunohistochemistry. Computed tomography and magnetic resonance imaging indicated metastases to multiple sites, including the lungs, lymph nodes, muscles, bones, and myocardium. Euthanasia was performed because of the rapid clinical deterioration of the dog’s condition. This case shows imaging features of synovial cell sarcoma similar to those described in human medicine, highlighting the clinical importance of advanced imaging for assessing the extent and metastasis of synovial cell sarcoma in dogs.