Diffuse abdominal epithelioid mesothelioma in a cow.

Mesotheliomas are rare in animals but occur spontaneously in many different species, including cattle, dogs, cats, swine, and horses (1,2), as well as in rats (3), blue foxes (4), and goats (1). In the bovine species, these tumors are more frequently observed in calves than in adults (1,2) and are considered to be congenital in young animals. Mesothelial tumors can take 2 different histologic patterns, a fibromatous one and an epithelioid one. The fibromatous form may mimic fibromas or fibrosarcomas (1,2). Epithelioid mesotheliomas must be differentiated from metastatic adenocarcinoma of the lungs, uterus, or gastrointestinal tract (1,2). Mesotheliomas may be multicentric and progress more by extension and implantation than by true metastasis (1,2). We report a case of diffuse abdominal epithelioid mesothelioma with tracheobronchial lymph node metastasis in an adult cow, confirmed by immunoperoxidase reactions for cytokeratin and vimentin intermediate filaments. A 14-year-old, Holstein cow from a herd of 34 adults, vaccinated for infectious bovine rhinotracheitis and fed with corn silage, hay, and concentrate, was examined for digestive problems. A marked decrease in milk production had been noted for some weeks. On 2nd examination 1 mo later, the cow was hypothermic and anorectic. Her abdomen was pendulous and pear-shaped, when viewed from the rear, with subcutaneous dependent edema. Results of a serological examination for leukosis were positive. Transrectal examination revealed the presence of multiple abdominal masses. A tentative clinical diagnosis of bovine leukosis was made. The animal was euthanized and a complete necropsy was done at the Faculty of Veterinary Medicine at Saint-Hyacinthe. The mammary veins were severely congested and the supramammary lymph nodes were enlarged and edematous, with hemorrhagic streaks on the cut surface. The thoracic cavity appeared normal, apart from enlargement of a tracheobronchial lymph node. About 30 L of serosanguineous fluid were present in the abdominal cavity. The parietal peritoneum and the rumenal serosa had a ground glass appearance and were hyperemic. The peritoneum was covered by numerous cauliflower-like, yellowish nodules, a few millimeters to 3 cm in diameter, that were often isolated and pedunculated. Sometimes, these nodules coalesced to form diffuse plaques on the peritoneal surface. Nodules were found on the serosal surface of many abdominal viscera (liver, gall bladder, spleen, pancreas, kidneys, urinary bladder, uterus, and ovaries) and on the diaphragm. These did not invade the subjacent parenchyma. Fibrin