Peritoneal Sarcomatoid Mesothelioma in cat

Resumo

Background: Mesothelioma is a malignant neoplasm of mesothelial cells that line the pleural, peritoneal, pericardial, and vaginal cavities of the testicles. Mesotheliomas are rare in all species and even more uncommon in cats. Diagnosis is based on histopathological and immunohistochemical findings. Clinical signs vary depending on the tumor’s location. The most common symptoms include dyspnea due to pleural effusion and abdominal distension caused by peritoneal effusion. The prognosis is poor, with low survival rates in affected animals. Treatment primarily consists of supportive care. This report describes a case of peritoneal sarcomatoid mesothelioma in a cat.

Case: A 7-year-old female cat was presented with abdominal distension, hyporexia, and weight loss over four days. Physical examination revealed marked abdominal distension, pale mucous membranes, and 8% dehydration. Abdominal ultrasound demonstrated significant peritoneal effusion and a reactive omentum. The leukogram revealed leukocytosis (40.4 x 10³/μl) due to neutrophilia (35.55 x 10³/μl), increased band neutrophils (0.81 x 10³/μl), eosinophilia (2.4 x 10³/μl), and lymphopenia (0.8 x 10³/μl). Abdominal fluid was collected and classified as a modified transudate; cytology revealed a few mesothelial cells. Due to the critical condition, the animal was hospitalized and received supportive treatment with cephalothin (20 mg/kg IV TID), metronidazole (15 mg/kg IV BID), vitamin B complex (0.2 mL/kg IV SID), and omeprazole (1 mg/kg IV SID). During hospitalization, the cat remained apathetic, receiving syringe feeding only. After three days without clinical improvement, the animal died. Necropsy revealed multiple whitish, irregular, firm, amorphous masses in the omentum. Histologically, over 90% of the cell population consisted of elongated neoplastic cells arranged in bundles and packets, supported by dense fibrous connective stroma—features consistent with peritoneal sarcomatoid mesothelioma. The neoplastic cells exhibited strong immunopositivity exclusively for the anti-vimentin antibody, confirming their mesenchymal origin.

Discussion: This case describes a rare occurrence of peritoneal sarcomatoid mesothelioma in a cat. The animal presented with apathy, anorexia, and abdominal distension—the latter being the hallmark of peritoneal mesothelioma. Unlike this case, mesotheliomas more commonly affect the pleural cavity. Ultrasonography and fluid analysis are helpful for distinguishing this condition from other causes of ascites. However, definitive diagnosis relies on histopathology and immunohistochemistry, which in this case were performed only postmortem. These tumors typically appear as multiple small nodules infiltrating the affected cavity or adjacent organs. The neoplastic cells were immunoreactive only to vimentin, characterizing a purely sarcomatoid neoplasm. Given the leukocytosis with neutrophilia, mild left shift, lymphopenia, and eosinophilia, along with ascites and peritonitis observed via ultrasound, effusive feline infectious peritonitis (FIP) was initially suspected. However, histological examination did not reveal hallmark features of FIP, such as predominantly pyogranulomatous perivascular inflammation, necrotizing phlebitis, or thrombosis. It is believed that the hematologic alterations were secondary to the inflammatory response induced by mesothelioma. In the absence of a premortem diagnosis, only supportive therapy was administered. This case highlights the diagnostic challenges and aggressive nature of peritoneal mesothelioma.