Aortic dissection is an uncommon finding in both dogs and cats. The precise pathophysiological mechanisms responsible for the development of aortic dissection remain unclear. In humans, aortic dissection is usually secondary to another systemic disease, such as systemic arterial hypertension, an abnormality of connective tissues or a parietal trauma. This is a case of an aortic dissection in a hypertensive hyperthyroid cat, presenting with haemorrhagic pericardial effusion. The dissection affected both thoracic and abdominal aorta, with histopathological confirmation. This case is an example of the utility of both thoracic and abdominal ultrasound for the diagnosis of aortic dissection in cats and it highlights the importance of rigorous clinical examination. Aortic dissection should be considered in the differential diagnosis of pericardial effusion in cats. Further investigations are fundamental to understand how dissections develop and extend to achieve good clinical results.
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