Peritoneal epithelioid mesothelioma in German shepherd dog - A case report

A seven-year-old intact German shepherd male dog was brought to Animal Disease Investigation Office, Bhuj, Government of Gujarat with complaint of testicular enlargement. On clinical examination bilateral enlargement of testes without accumulation of any transudate/exudate in scrotum was noticed, hence bilateral orchiectomy was performed. At the time of surgery, multifocal to coalescing, raised, soft to firm, off-white, 0.1 to 1 cm diameter nodules, randomly scattered over the tunica vaginalis of testes were noted. After two days of surgery, dog showed blood tinged vomitus and lethargy. Although, dog was treated symptomatically, animal was died on the next day. On post mortem examination, the serosal surfaces of the abdominal viscera, internal abdominal wall and diaphragm were studded with multifocal to coalescing, raised, soft to firm, off-white, 0.1 to 2 cm diameter nodules. Mild ascites was noted. Appropriate samples were collected in 10% neutral buffered formalin and submitted for histopathology. Microscopic examination revealed, neoplastic cells expanding and elevating the serosal surface of most visceral organs, testes and wall of abdomen. The neoplastic mesothelial cells showed resemblance with epithelial cells and exhibited various cytoplasmic and nuclear features of malignancy such as moderate to abundant quantity of eosinophilic cytoplasm, variably distinct cell border, round to oval large vesicular nuclei with centrally placed prominent nucleoli, occasional mild anisokaryosis, karyomegaly and mitotic figures less than one per high power field. On immunohistochemical examination, neoplastic cells showed strong cytoplasmic immunoreactivity with cytokeratin and vimentin and negative for smooth muscle actin and S-100. On the basis of gross, microscopic and immunohistochemical examination, the growth was diagnosed as peritoneal malignant epithelioid mesothelioma.