Joint tumors are uncommon in dogs and very rare in cats. Joint tumor is a misnomer as tumors of the articular cartilage have not been reported. Periarticular tumors is a more accurate term. The most common periarticular tumors in dogs are synovial cell sarcoma, histiocytic sarcoma, myxosarcoma and myxoma, and various other sarcomas. The majority of periarticular tumors are malignant and the risk of metastasis depends on tumor type and, for some tumors such as synovial cell sarcoma, histologic grade.
Synovial cell sarcomas most commonly involve the stifle joint, but can involve any joint. Flat-Coated Retrievers and Golden Retrievers are predisposed to periarticular synovial cell sarcomas.
A relationship between previous joint disease and the development of periarticular histiocytic sarcoma has been identified in Bernese Mountain Dogs, with periarticular histiocytic sarcoma 5.4-times more likely to develop in a diseased joint.
Radiographs are recommended initially, however all periarticular tumors have a similar radiographic appearance. Typical radiographic changes include a partially lobulated soft tissue mass adjacent to a joint, tendon sheath, or bursa, with involvement of two or more bones (100% of cases) and bone destruction in 11%-45% of dogs (and up to 72% in one study). The bone destruction may be smooth and well-delineated as a result of pressure necrosis from an expansile mass, or less distinctive lysis as a result of soft tissue infiltration of bone. Advanced imaging with either contrast-enhanced CT scans or MRI can assist in further determing the presence of a periarticular mass and the extent of disease for surgical planning. A definitive diagnosis requires both histopathology and immunohistochemistry, with the latter often required to differentiate synovial cell sarcoma from histiocytic sarcoma.
The regional lymph nodes and lungs are the most common sites for metastasis of synovial cell and histiocytic sarcomas. Fine-needle aspiration of the regional anatomic lymph node or sentinel lymph node mapping and biopsy are recommended to assess for nodal metastasis. Sentinel lymph node mapping involves peritumoral injection of a lipid-soluble contrast agent 24 hours prior to surgery (usually under sedation), regional radiographs immediately prior to surgery to identify the sentinel lymph node, and then peritumoral blue dye injection during surgery to aide in intraoperative identification and excision of the sentinel lymph node.
Thoracic radiographs or CT scans are recommended to assess the lungs for metastasis.
The recommended treatment for dogs and cats with periarticular tumors is limb amputation. The decision to proceed with limb amputation is often difficult. However, cats have excellent function and the vast majority of dogs have good to excellent function following limb amputation. The only contraindication for limb amputation is pre-existing neurologic disease. Large breed dogs, obese dogs, and dogs with osteoarthritis are often good candidates for limb amputation. The majority of dogs can walk unassisted 1-2 days after surgery. The median time to maximal recovery is 4 weeks, but this time is significantly shorter for dogs with owners who are positive about the amputation procedure. There is no difference in recovery rates or mobility following amputation of either the fore or hind limb. In a study published in 2015 in which 64 owners of dogs with amputated limbs were surveyed, 91% of owners perceived no change in their dog's attitude after limb amputation, 88% of owners reported complete or near complete return of their dog to pre-amputation quality of life, 78% indicated that their dog's recovery and adaption were better than they had expected; and 73% reported no change in their dog's recreational activities.
Please visit www.tripawds.com for more information on limb amputation and living with a three-legged pet. Images and videos of three-legged dogs can be found at www.animalcancersurgeon.com/bone-tumors-appendicular.
Palliative radiation therapy has been reported in one dog with a grade III synovial cell sarcoma, and this dog lived for13 months prior to developing a metastatic splenic hemangiosarcoma.
The role of chemotherapy for synovial cell sarcomas and other types of soft tissue sarcomas is unknown, but should be considered for dogs with grade III synovial cell sarcomas because of the high risk of distant metastasis. Chemotherapy with CCNU (or lomustine) is recommended for dogs with periarticular histiocytic sarcoma.
Synovial Cell Sarcoma
The prognosis for dogs with synovial cell sarcoma depends on clinical stage, surgical treatment, and histologic grade. Local tumor recurrence is common following conservative surgery. Metastasis is reported in 8%-32% dogs with synovial cell sarcoma, with the regional lymph nodes and lungs the most common sites of metastasis.
The overall median survival time following surgical excision is 455 days to 967 days, and this is significantly better than the median survival time of 93 days for untreated dogs. The median survival time for dogs with metastasis at the time of diagnosis is < 6 months which is significantly worse than the median survival time of 36-48 months when there is no evidence of metastasis at the time of diagnosis. The median survival time following conservative surgical resection is 455 days compared to 840 days when treated with limb amputation. The median survival times for dogs with grade I, II, and III synovial cell sarcomas are 365-1460 days, 156-1095 days, and 183 days, respectively.
The prognosis for dogs with periarticular histiocytic sarcoma depends on treatment protocols. Metastasis is reported in up to 91% dogs with periarticular histiocytic sarcoma, with the regional lymph nodes and lungs the most common sites of metastasis. The median survival times for untreated dogs and dogs treated with limb amputation and limb amputation combined with CCNU chemotherapy are 61 days, 161 days, and 568 days, respectively.
Last updated on 6th March 2017