Cardiac tamponade in a cat with pericardial mesothelioma.

Pericardial effusion is uncommon in cats and most often secondary to congestive heart failure, feline infectious peritonitis or neoplasia. Primary cardiac tumors are rare in companion animals, with their occurrence being particularly uncommon in cats and among these, mesothelioma is exceptionally rare. Its antemortem diagnosis presents a considerable challenge due to the often-mild nature of intrapericardial fluid accumulation and the difficulty in cytologically differentiating neoplastic cells from reactive mesothelial cells. A 12-year-old Domestic Shorthair cat was presented for dyspnea and weakness. Ultrasound examination revealed concurrent pleural, peritoneal and pericardial effusion. Pericardial effusion appeared densely particulate with multiple small nodules on the epicardial surface. Pericardiocentesis acutely resolved the cardiac tamponade, but recurrence prompted subtotal pericardiectomy. Histopathology of surgical biopsies suggested pericardial mesothelioma. Despite surgery, the cat’s clinical condition deteriorated, leading to euthanasia one month later. Autopsy, histopathology and immunohistochemistry (positive for cytokeratin AE1/AE3, vimentin, calretinin and HBME-1) confirmed pericardial mesothelioma with pleural dissemination. This report describes the clinical, diagnostic, and pathological features of a rare case of feline pericardial mesothelioma and highlights the diagnostic value of a multimodal approach.