Canine Synovial Sarcoma of the Stifle Joint with Pulmonary and Liver Metastases

A seven-year-old female mongrel dog was presented at the Sokoine University of Agriculture Teaching Animal Hospital for second opinion regarding a progressive swelling of the right hind limb of two months duration. Clinical examination revealed a loss of body condition, tachypnea and tachycardia, a painful immobile solid mass of 20 cm x 14 cm x 10 cm located on the right stifle joint, leucocytosis, and anaemia. Radiographic examination of the joint revealed marked soft tissue swelling with amorphous areas of mineralization and complete destruction of the proximal tibia. Smooth and solid periosteal reaction was seen around the tibia and fibula with a Codman’s triangle. Multiple nodules and a mass with soft tissue opacity were seen in the lung fields. Post-mortem examination revealed separation of tibia and fibula, softening of the proximal parts of the tibia, and complete integration of the proximal region of the two bones and articular tissues into the surrounding muscular tissues. Multifocal nodular lesions of variable sizes were mostly found in the lungs and partly in the liver. Histologically, predominantly oval and round cells with variable nuclear sizes and moderate mitoses were observed in tissue samples from the joint, lungs and the liver although some parts of the lung metastases showed both round and spindle shaped tumor cells. Clinical profile is suggestive of aggressive biphasic (spindle and epithelial) type of synovial cell sarcoma with lung and liver metastasis. Early radiographic and biopsy examination of persistent musculoskeletal nodules is recommended for early diagnosis and interventions.