Periarticular histiocytic sarcoma of a thoracic limb in a Rottweiler

An 8-year-old, castrated, male Rottweiler was referred for evaluation of chronic right thoracic limb lameness and a progressively growing mass surrounding the right elbow joint. On admission, the dog's general health was good, without abnormalities detected on physical examination. The dog was diagnosed with periarticular histiocytic sarcoma. Although draining lymph nodes and lung metastases were suspected, palliative amputation was performed. Localized histiocytic sarcomas, with destructive lesions involving multiple bones of a joint and periarticular soft-tissue masses, are uncommon in dogs. This case report presents clinical findings, imaging characteristics, and histopathologic and immunohistochemical features of a periarticular joint histiocytic sarcoma.