Synovial cell sarcoma in a dog: A misnomer—Cytologic and histologic findings and review of the literature

Abstract

A 4-year-old Irish Setter was presented with a history of progressive left pelvic limb lameness. Orthopedic examination revealed pain on manipulation of the left stifle. Radiographs showed an osteolytic lesion in the subchondral bone of the medial tibial condyle. Fine-needle aspirates were taken, and cytology revealed numerous cohesive clusters of plump, oval to spindloid cells often with perivascular distribution and moderate cellular atypia. A diagnosis of sarcoma was made with synovial cell sarcoma (SCS) and histiocytic sarcoma being the 2 main differentials. Histopathology confirmed the diagnosis of sarcoma and provided the same differentials. All neoplastic cells were positive for vimentin, and approximately 5% of them also stained with pan-cytokeratin using immunohistochemical staining methods. Neoplastic cells did not express CD18. The combination of this immunohistochemical profile and cell morphology was consistent with an SCS. Synovial cell sarcoma is a rare and poorly understood canine tumor entity. This is the first extensive description of the cytologic features of this neoplasm. The literature was also reviewed, focusing on comparative aspects of dogs and people, with a special emphasis on the cell of origin and diagnostic tools. Controversies regarding the nomenclature of this tumor are also presented. The authors propose a new term (cytokeratin-positive joint-associated sarcoma) for addressing this neoplasm until the cell of origin of this tumor is elucidated.

Imaging features of benign synovial inflammation affecting the long digital extensor tendon sheath in a dog

“…8 The incidence of metastatic disease secondary to synovial cell sarcoma is not well described, but pulmonary metastases and hypertrophic osteopathy developed in one dog 10 months following diagnosis. 3 The presence of pulmonary soft tissue nodules biased this case towards a diagnosis of malignancy. Small or ill-defined pulmonary nodules can have variable significance, 9,10 as in this case where histopathology was consistent with granulomas.…”

“…Pathology of the LDET and sheath is uncommon in adult dogs, although tendinopathy or rupture secondary to trauma or mechanical injury 1,2 and neoplasia may occur in this region. [3][4][5][6] A relationship between LDET injury with CrCL injury has been postulated. 2 In this case, there was minimal cruciate ligament degeneration on MRI and the dog had a low activity level with no recent history of trauma.…”

“…Pathology of the LDET and sheath is uncommon in adult dogs, although tendinopathy or rupture secondary to trauma or mechanical injury 1,2 and neoplasia may occur in this region 3–6 . A relationship between LDET injury with CrCL injury has been postulated 2 .…”

“…Based on the clinical history, signalment, regionally infiltrative intrasynovial mass, and pulmonary nodules, neoplasia such as a soft tissue sarcoma was considered a top differential. Synovial cell sarcoma has been reported in dogs affecting the LDET sheath and stifle, although it remains a relatively uncommon and poorly understood tumor 3,4 . Imaging characteristics may include increased soft tissue with focal regions of osteolysis on radiographs 3,4 and contrast enhancement on MRI 4 .…”

“…Synovial cell sarcoma has been reported in dogs affecting the LDET sheath and stifle, although it remains a relatively uncommon and poorly understood tumor 3,4 . Imaging characteristics may include increased soft tissue with focal regions of osteolysis on radiographs 3,4 and contrast enhancement on MRI 4 . Masses associated with tendons and ligaments may grow into surrounding muscle and bone without joint involvement 7 .…”