Ovarian papillary adenocarcinoma in a Yorkshire terrier dog

A 10-year-old intact female Yorkshire terrier dog was referred for evaluation of marked abdominal distension and hemorrhagic effusion. Abdominal radiography and ultrasonography demonstrated abdominal effision and intraabdominal mass with anechoic cystic components. On ascites cytology, neoplastic epithelial cells with vacuolated cytoplasm and prominent nucleoli were identified. Magnetic resonance imaging (MRI) showed the well-defined, heterogeneous, and large mass filled the intraabdominal cavity. At necropsy, a large mass ansirig from the right ovary was observed. Histopathologically, the mass was composed of papillary structures lined by neophastic epithelial cells. The dog was definitively diagnosed as malignant ovarian adenocarcinoma with papillary pattern based on clinical and histopathological findings.