Mesotelioma peritoneal sarcomatoide em gato

Abstract

Background: Mesothelioma is a malignant neoplasm of mesothelial cells that line the pleural, peritoneal, pericardial and vaginal cavities of the testicles. They are rare in all species and even less common in cats. The diagnosis is made by histophatological and immunohistochemical findings. Clinical signs depend on the location of the tumor. The most common symptoms include dyspnea due to pleural effusion and abdominal distension caused by peritoneal effusion. The prognosis is poor, and survival rates in affected animals are low. Treatment primarily consists of supportive care. The objective of this study is to report a case of peritoneal sarcomatoid mesothelioma in a cat. Case: A female cat, of approximately 7 years of age, was admitted with abdominal distension, hyporexia and weight loss for 4 days. The physical examination revealed marked abdominal distension, pale mucous membranes and 8% dehydration. Abdominal ultrasound showed marked abdominal effusion and reactive omentum. The leukogram showed leukocytosis (40.4 x 103 /μl) due to neutrophilia (35.55 x 103 /μl), increased number of rods (0.81 x 103 /μl), eosinophilia (2.4 x 103 /μl) and lymphopenia (0.8 x 103 /μl). Abdominal fluid was collected for analysis and classified as modified transudate, and cytology showed rare mesothelial cells. Due to the critical condition, the animal was hospitalized. Treatment was administered with cephalothin [20 mg/kg, IV, TID] and 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 animal remained apathetic, feeding only through a syringe. After three days, with no clinical improvement, the animal passed away. After necropsy, macroscopic analysis showed multiple whitish, irregular, amorphous and firm masses in the omentum. Histologically, more than 90% of the cell population was composed of elongated neoplastic cells, organized in bundles and packets, supported by a dense fibrous connective tissue stroma, characterizing peritoneal sarcomatoid mesothelioma. These neoplastic cells showed strong immunoreactivity to anti-vimentin antibody, confirming their mesenchymal origin. Discussion: This report highlights a case of peritoneal sarcomatoid mesothelioma in a cat. The animal exhibited apathy, anorexia, and abdominal distension, the latter being the primary symptom of peritoneal mesothelioma. Unlike the reported case, mesothelioma more commonly affects the pleural cavity. Ultrasound and fluid analysis are useful in differentiating this condition from other causes of ascites. However, the definitive diagnosis of mesothelioma is based on histopathology and immunohistochemistry of the tumor, which, in this case, were performed only postmortem. These tumors appear as multiple small nodules invading the affected cavity or adjacent organs. The neoplastic cells were positive only for the anti-vimentin antibody, characterizing a purely sarcomatoid neoplasm. Given the leukocytosis with neutrophilia, mild left shift, lymphopenia, and eosinophilia in the leukogram, associated with ascites and peritonitis observed on ultrasound, effusive FIP was initially suspected. However, histological analysis did not reveal characteristic findings of FIP, such as predominantly pyogranulomatous inflammation around blood vessels, necrotizing phlebitis, and thrombosis, which are typically present in the disease. It is believed that the leukogram alterations were caused by the inflammatory process induced by mesothelioma. Without a pre-mortem diagnosis, the animal received only supportive treatment until death. This case highlights the diagnostic challenges of peritoneal mesothelioma and its aggressive nature.