Mesothelioma in Two Nondomestic Felids: North American Cougar (Felis concolor) and Cheetah (Acinonyx jubatus)

A 15-year-old male North American cougar (Felis concolor) presented with a 2-day history of anorexia, restlessness, and dyspnea. White blood cell count ( ？cells/μL) and absolute segmented neutrophil count ( ？cells/μL) were increased, and BUN (143？mg/dL), creatinine (6.3？mg/dL), and phosphorus (8.5？mg/dL) concentrations indicated chronic renal disease. Thoracic radiographs showed severe pleural and pericardial effusion. During attempts to remove the fluid, cardiac tamponade developed and the cat died. At necropsy, nodular masses decorated the pericardium at the level of the base of the heart. The final microscopic diagnosis was mesothelioma of the pericardium, tunica adventitia of the main pulmonary artery, left auricle epicardium, and left ventricular epicardium. A 15-year-old female cheetah (Acinonyx jubatus) was evaluated for acute respiratory distress. The white blood cell count ( ？cells/μL) and absolute segmented neutrophil count ( ？cells/μL) were increased. Radiographically pleural effusion and a cranial thoracic mass were seen. The cheetah was euthanized, and a gross diagnosis of disseminated pleural mesothelioma with thoracic effusion was made. Histologically, pleural mesothelioma was confirmed with local invasion of the lung and pulmonary arterial emboli and infarction. In both cases, a diagnosis of mesothelioma was made based on cellular morphology, microscopic architecture, and neoplastic cell coexpression of cytokeratin and vimentin. 1. Introduction Mesothelioma is a neoplasm involving cells that line the coelomic cavities of the body and can occur as either a widespread nodular mass or multifocal masses. Mesothelial tumors are considered malignant due to their ability to seed throughout a body cavity resulting in numerous tumors and implantation metastasis; however, spread into noncommunicating body cavities is considered rare [1]. In domestic dogs, primary mesothelial tumors have been reported affecting the thoracic cavity, pericardial sac, abdominal cavity, and vaginal tunics of the scrotum [1]. In domestic cats, primary mesotheliomas have been reported in the pericardium, pleura, peritoneum, and the abdomen with pulmonary and nodal metastases [1–6]. While pleural mesotheliomas have been reported in tigers and clouded leopards (Neofelis nebulosa nebulosa), pericardial mesotheliomas are rarely reported in both domestic and nondomestic species [7–9]. A common clinical sign of affected animals is pronounced dyspnea caused by pleural effusion or compression from peritoneal effusion. Marked effusions from direct exudation of the tumor or from