Primary ovarian rhabdomyosarcoma in a dog.

A 10-year-old female English pointer was diagnosed with an ovarian tumour with abdominal metastases. Ultrasonography revealed several nodules of 1-5 cm diameter within the abdominal cavity. Fine needle aspiration cytology of the nodules suggested a malignant mesenchymal tumour. On necropsy examination the right ovary and its capsule were enlarged and there were white-red, friable nodular masses distributed over the surface of the pancreas, liver, omentum, mesentery and serosae of the small and large intestines. Microscopical evaluation revealed neoplastic cells with a high degree of pleomorphism and vascular invasion. Immunohistochemically, the neoplastic cells expressed myosin, desmin, vimentin and CD10, but were negative for cytokeratin, placental alkaline phosphatase, inhibin-alpha and smooth muscle actin. Based on these findings a diagnosis of primary ovarian alveolar rhabdomyosarcoma was made.