History
A 6-year-old sexually intact male Bernese Mountain Dog was referred to the medicine service at the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania for weight loss and right pelvic limb lameness of 1 years' duration. Previously, immune-mediated polyarthropathy was suspected on the basis of findings on cytologic evaluation of synovial fluid, joint radiography, and serologic testing for antibodies against Babesia canis, Borrelia burgdorferi, Anaplasma phagocytophilum, and Ehrlichia canis. The dog was treated with doxycycline and prednisone, which improved the lameness but not the weight loss. At the time of admission, the dog was in poor body condition with generalized muscle atrophy. Physical examination revealed considerable amounts of soft tissue swelling surrounding the right stifle joint. Signs of pain were elicited by manipulation of the stifle joint, which was associated with moderate joint instability as evidenced by detection of a cranial drawer sign. A CBC and serum biochemical analysis revealed a moderated nonregenerative anemia and mildly high serum globulin concentration as well as high serum aspartate aminotransferase and alkaline phosphatase activities. Findings on thoracic radiography were unremarkable. On abdominal ultrasonography, enlargement of both medial iliac lymph nodes was observed. Cytologic evaluation of ultrasound-guided fine-needle aspirates of these lymph nodes revealed reactive lymphoid hyperplasia. Radiographic images of the right stifle joint were obtained (Figure 1).
Lateral (A) and craniocaudal (B) radiographic views of the stifle joint in a 6-year-old sexually intact male Bernese Mountain Dog with pelvic limb lameness and weight loss.
Citation: Journal of the American Veterinary Medical Association 236, 12; 10.2460/javma.236.12.1293
Lateral (A) and craniocaudal (B) radiographic views of the stifle joint in a 6-year-old sexually intact male Bernese Mountain Dog with pelvic limb lameness and weight loss.
Citation: Journal of the American Veterinary Medical Association 236, 12; 10.2460/javma.236.12.1293
Lateral (A) and craniocaudal (B) radiographic views of the stifle joint in a 6-year-old sexually intact male Bernese Mountain Dog with pelvic limb lameness and weight loss.
Citation: Journal of the American Veterinary Medical Association 236, 12; 10.2460/javma.236.12.1293
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
A soft tissue mass is associated with the stifle joint; it appears to obliterate the infrapatellar fat pad almost completely and displace the caudal fascial planes caudally (Figure 2). The soft tissue mass extends into the cranioproximal region of the femoropatellar joint with displacement of the patella medially. There is mild osteophytosis of the apex of the patella and both femoral condyles. Multifocal lysis in the medial femoral condyle, the intercondylar fossa, and the proximal portion of the tibia just distal to the intercondyloid tubercles is visible. Muscle atrophy is evident. The presumptive diagnosis was a polyostotic aggressive lesion of the stifle joint such as histiocytic sarcoma, synovial myxoma, synovial cell sarcoma, osteosarcoma, multiple myeloma, lymphosarcoma, bacterial or fungal osteomyelitis, or metastatic neoplasia. Other differential diagnoses, such as severe proliferative synovitis, were considered much less likely.
Same radiographic views as in Figure 1. On the lateral view, notice the large soft tissue mass, obliterating the infrapatellar fat pad and the caudal fascial planes. The mass is outlined by arrowheads. On both views, areas of lysis (black arrows) can be seen in the femoral condyles and in the proximal aspect of the tibia. Some osteophytes consistent with osteoarthritis are present on the patella and the distal aspect of the femur. The patella is medially luxated on the craniocaudal view; it is unclear whether this is caused by the mass or represents a preexisting condition.
Citation: Journal of the American Veterinary Medical Association 236, 12; 10.2460/javma.236.12.1293
Same radiographic views as in Figure 1. On the lateral view, notice the large soft tissue mass, obliterating the infrapatellar fat pad and the caudal fascial planes. The mass is outlined by arrowheads. On both views, areas of lysis (black arrows) can be seen in the femoral condyles and in the proximal aspect of the tibia. Some osteophytes consistent with osteoarthritis are present on the patella and the distal aspect of the femur. The patella is medially luxated on the craniocaudal view; it is unclear whether this is caused by the mass or represents a preexisting condition.
Citation: Journal of the American Veterinary Medical Association 236, 12; 10.2460/javma.236.12.1293
Same radiographic views as in Figure 1. On the lateral view, notice the large soft tissue mass, obliterating the infrapatellar fat pad and the caudal fascial planes. The mass is outlined by arrowheads. On both views, areas of lysis (black arrows) can be seen in the femoral condyles and in the proximal aspect of the tibia. Some osteophytes consistent with osteoarthritis are present on the patella and the distal aspect of the femur. The patella is medially luxated on the craniocaudal view; it is unclear whether this is caused by the mass or represents a preexisting condition.
Citation: Journal of the American Veterinary Medical Association 236, 12; 10.2460/javma.236.12.1293
Comments
Incisional biopsy specimens of the soft tissue mass were obtained. Histologic evaluation revealed histiocytic sarcoma. Synovial tumors have traditionally been thought to be overrepresented by synovial cell sarcomas.1,2 However, in 1 study,2 histiocytic sarcoma was the most common synovial tumor (51.4%), being more than 3 times as common as synovial cell sarcoma (14.3%) and synovial myxoma (17.1%). Other synovial tumors include fibrosarcoma, chondrosarcoma, and undifferentiated sarcoma. Although Bernese Mountain Dogs have the highest prevalence for the systemic form of histiocytosis,1–5 this is not the case for the skeletal manifestation of the disease, for which Rottweilers and Golden Retrievers are by far the most commonly affected breeds.1 Many Rottweilers in 1 study2 had a history of cranial cruciate ligament rupture, which has been associated with ongoing chronic synovitis. The authors of that study hypothesized that the histiocytic sarcomas arise from the dendritic cells found within the inflamed synovium.2 In the dog of the present report, cruciate ligament rupture was suspected on the basis of clinical examination and radiographic evidence of mild osteoarthritis.
Skeletal lesions caused by histiocytic sarcoma can be grouped into periarticular, vertebral, humeral, and rib lesions. Bone lesions are aggressive, predominantly lytic lesions that are usually associated with a soft tissue mass, except in instances that involve the proximal aspect of the humerus or the hip joint, for which a soft tissue mass is typically not present.1 Radiographic findings for the dog of this report were also mainly lytic bone lesions associated with a large soft tissue mass. Osteophytes associated with the stifle joint were smooth and well mineralized and therefore were thought to represent mild osteoarthritis consistent with a cranial cruciate ligament rupture as suspected clinically on the basis of a cranial drawer sign.
Skeletal histiocytic sarcoma can cause systemic disease, in which multiple organ systems are affected, or localized disease with or without regional lymphadenopathy.3 Metastatic spread can occur and is associated with a grave prognosis. In the dog of the present report, no other lesions were found on thoracic radiography and abdominal ultrasonography. However, systemic involvement (disseminated or metastatic) cannot be completely ruled out because the dog had nonregenerative anemia of unknown origin and a history of weight loss. The dog was managed with pain medication and was euthanatized several weeks after the diagnosis.
- 1.↑
Shultz RM, Puchalski SM & Kent M, et al. Skeletal lesions of histiocytic sarcoma in nineteen dogs. Vet Radiol 2007;48:539–543.
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Craig LE, Julian ME, Ferracone JD. The diagnosis and prognosis of synovial tumors in dogs: 35 cases. Vet Pathol 2002;39:66–73.
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Rosin A, Moore P, Dubielzig R. Malignant histiocytosis in Bernese Mountain Dogs. J Am Vet Med Assoc 1986;188:1041–1045.
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Ramsey IK, McKay JS & Rudorf H, et al. Malignant histiocytosis in three Bernese Mountain Dogs. Vet Rec 1996;138:440–444.
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Affolter VK, Moore PF. Localized and disseminated histiocytic sarcoma of dendritic cell origin in dogs. Vet Pathol 2002;39:74–83.
