Canine Synovial Myxoma

Abstract

This report describes the signalment, clinical findings, gross appearance, histological and immunohistochemical characteristics, and behavior of 39 cases of canine synovial myxoma. Large-breed middle-aged dogs-especially, Doberman Pinschers and Labrador Retrievers-were most commonly affected. The stifle and digit were the most common sites. Grossly, the tumors were composed of gelatinous nodules that often filled the joint cavity and exuded viscous fluid on cut section. In 12 cases (31%), radiographic bony lysis or grossly invasive growth was noted clinically. Histologically, the nodules were sparsely cellular and composed of stellate to spindle cells suspended in an abundant myxomatous matrix. By immunohistochemistry, the cells were positive for vimentin, heat shock protein 25, and cadherin 11 and negative for cytokeratin and S100 protein; some cells (20-40%) were positive for CD18. Affected dogs had long survival times (average, 2.5 years), even with incomplete excision of the tumor. Three cases had local recurrence, but none metastasized or directly resulted in death. Canine synovial myxoma is a histologically distinctive tumor with a good prognosis.

Incidental Synovial Myxoma with Extensive Intermuscular Infiltration in a Dog

“…Renal adenocarcinoma was confined to the left kidney; no metastasis was detected. The gross and histopathologic findings of the joint and intermuscular masses were consistent with those of canine synovial myxoma [1][2][3]. Muscle infiltration of synovial myxoma has been reported in some cases [3,4], but little is known about the histopathology of the muscle lesions.…”

“…The gross and histopathologic findings of the joint and intermuscular masses were consistent with those of canine synovial myxoma [1][2][3]. Muscle infiltration of synovial myxoma has been reported in some cases [3,4], but little is known about the histopathology of the muscle lesions. In the present study, we report for the first time the histopathologic findings of muscle lesions of synovial myxoma, including the cystic structures lined by synoviocyte-like cells.…”

“…Synovial myxoma is a unique lesion of the synovium and one of the most common joint tumors in dogs, especially large-breed middle-aged dogs [1][2][3]. They are characterized by myxomatous nodules protruding into the joint cavity, with proliferation of cells resembling both type A and b synoviocytes; the cellular origin of the tumor is still undetermined.…”

“…They are characterized by myxomatous nodules protruding into the joint cavity, with proliferation of cells resembling both type A and b synoviocytes; the cellular origin of the tumor is still undetermined. Synovial myxoma has a good prognosis with long survival time, even with incomplete excision of the tumor [3]. Local recurrence is rare, and metastasis has not been reported.…”

“…Local recurrence is rare, and metastasis has not been reported. They sometimes invade the bone and extend beyond the joint capsule, infiltrating along fascial planes of adjacent muscles [3,4]. However, the histopathology of the muscle infiltration of the tumor has not been well described.…”