Metastatic renal extraskeletal osteosarcoma in a dog: Clinical presentation, CT features and the role of ALP cytochemical staining for diagnosis

A 7-year-old beagle dog referred for investigations of haematuria was diagnosed with an amorphous mineralised mass of the right kidney and distant metastasis to several muscles, lymph nodes, interventricular septum, diaphragm and pulmonary parenchyma. Cytological examination of ultrasound-guided fine-needle aspirates taken from the right renal mass, right perineum nodule and abdominal wall nodules diagnosed a sarcoma with osteoblastic differentiation. Alkaline phosphatase cytochemical staining was performed on the slides from the renal aspirate and supported the diagnosis of an osteosarcoma. Due to the poor prognosis and extensive metastatic disease, the dog was euthanased. Computed tomography characteristics are described, as well as the use of alkaline phosphatase cytochemical staining, for diagnosis of extraskeletal osteosarcomas in dogs.