History
A 10-year-old spayed female Persian cat was referred for evaluation of a mass in the area of the left elbow joint that had been steadily increasing in size for more than 2.5 months without inducing lameness or signs of pain. The cat's vaccination status was adequate, and there was no history of travel outside New York state. Seven months before referral, the cat had been treated successfully for hyperthyroidism with radioiodine. Diagnostic evaluation prior to referral included radiographic examination of the left thoracic limb, which revealed signs of osteoarthrosis. A viscous fluid was obtained during fine-needle aspiration of the mass. Physical examination of the cat at the time of referral revealed a 4-cm, multilobular, smooth, firm mass over the cranial aspect of the left elbow joint. The skin covering the mass was freely moveable, but the mass adhered to the underlying tissues. Signs of pain were not elicited during examination. Results of a CBC and serum biochemical analyses were within reference ranges. Radiographs of the left elbow joint were obtained (Figure 1).
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Radiographic Findings and Interpretation
At the craniomedial aspect of the elbow joint, there is a large (approx 3-cm diameter) juxta-articular soft tissue mass. In the humeral condyle, there are a few radiolucent areas. At the cranial aspect of the elbow joint, there is a triangular, periarticular, mineralized body. At the medial aspect of the elbow joint, there is mild periarticlar new bone formation (severe osteoarthrosis). The lucent lesions in the humerus were possibly associated with the mass or with osteoarthrosis (Figure 2).
Comments
Excisional biopsy of the left elbow joint mass was performed. Histologic evaluation of the biopsy specimen revealed low-grade synovial cell sarcoma. The cat was returned 6 weeks later for amputation of the left thoracic limb. Physical examination revealed recurrence of the soft tissue mass on the medial and lateral aspects of the left elbow joint. No other abnormalities were found on physical examination. Results of a CBC and serum biochemical analyses were within reference ranges. Three-view thoracic radiography did not reveal metastatic disease. Amputation of the left thoracic limb and removal of the left axillary lymph node were performed. Histologic evaluation of the left thoracic limb revealed recurrent synovial cell sarcoma without evidence of metastasis to the lymph node.
Synovial cell sarcoma is a rare tumor in animals and occurs more commonly in dogs than in cats. Only 5 cases in cats have been reported in the literature.1,2 These cats ranged in age from 6 to 9 years old, and most were lame.1,2 In 3 cats, the mass did not invade adjacent bone structures or metastasize, although incomplete excision resulted in recurrence of the mass.1 In the remaining 2 cats, radiography revealed bony lysis and periosteal reactions adjacent to the soft tissue tumor.1,2 Amputation was performed, with no evidence of tumor recurrence or metastasis up to 7 months after amputation.
Synovial cell sarcoma is diagnosed predominantly in large-breed and middle-aged dogs.3 Reports4–7 conflict as to a sex predisposition. The stifle and elbow joints are the most frequent sites, and common clinical signs include a nonpainful, palpable mass with variable rate of growth and lameness that correlates with the extent of bone lysis detected radiographically.3,4,6,7
Radiographic signs include a homogeneous soft tissue mass with or without bone involvement consisting of periosteal or periarticular new bone and cortical, cancellous, and punctate to moth-eaten bony lysis on both sides of the joint.3
Grossly, synovial cell sarcomas are lobules of cystlike spaces filled with mucinous fluid that infiltrate through fascial planes and connect to the joint capsule.3 Synovial cell sarcomas stain for vimentin and can stain for cytokeratin.3,5,7 It is questionable whether mitotic index, degree of nuclear pleomorphism, and percentage of tumor necrosis have a role in prognosis.5–7
The metastatic potential of synovial cell sarcoma in dogs has been reported3,4,6 to be as high as 54%, with metastasis to the lung and lymph nodes from 4 months to > 1 year after diagnosis. In 1 study,7 median survival times were 840 and 455 days, respectively, for dogs that underwent amputation and marginal excision. Mean survival time without treatment was 93 days. The tumor tends to recur with local excision, but dogs whose limbs are amputated may live disease free for > 5 years, with a recurrence rate of 7% at the amputation site.5,6 Adjunctive treatment with chemotherapy or orthovoltage radiation in dogs with and without metastatic disease has been reported with variable response rates and disease-free intervals.4–7
- 1↑
Silva-Krott IU, Tucker RL, Meeks JC, et al. Synovial sarcoma in a cat. J Am Vet Med Assoc 1993;203:1430–1431.
- 2
Borenstein N, Fayolle P, Moissonnier P. What is your diagnosis? Synovial sarcoma. J Small Anim Pract 1999;40: 205, 236–237.
- 3↑
Pool RR, Thompson KG. Tumors of joints. In:Meuten DJ, ed.Tumors in domestic animals. 4th ed.Ames, Iowa: Iowa State Press, 2002;227–233.
- 4
McGlennon NJ, Houlton JF, Gorman NT. Synovial sarcoma in the dog—a review. J Small Anim Pract 1988;29:139–152.
- 5
Craig LE, Julian ME, Ferracone JD. The diagnosis and prognosis of synovial tumors in dogs: 35 cases. Vet Pathol 2002;39:66–73.
- 6
Vail DM, Powers BE, Getzy DM, et al. Evaluation of prognostic factors for dogs with synovial sarcoma: 36 cases (1986–1991). J Am Vet Med Assoc 1994;205:1300–1307.
- 7↑
Fox DB, Cook JL, Kreeger JM, et al. Canine synovial sarcoma: a retrospective assessment of described prognostic criteria in 16 cases (1994–1999). J Am Anim Hosp Assoc 2002;38:347–355.