Incidentally diagnosed non-dissecting thoracic aortic aneurysm in a dog with suspected aortic valve abnormality.

A thoracic aortic aneurysm (TAA) is a relatively common cardiovascular disorder in humans. However, it is rarely reported in dogs. To date, several reported canine cases are associated with clinical signs and severe complications, such as aortic dissection and rupture. Herein, we report an incidentally diagnosed TAA in an asymptomatic elderly dog with suspected aortic valve abnormality. A 12-year-old spayed female Shiba Inu was referred for the evaluation of anorexia and vomiting. It was subsequently diagnosed with gallbladder mucocele. Thoracic radiography revealed cranial mediastinal widening, and transthoracic echocardiography showed marked dilation of the thoracic aorta distal to the sinus of Valsalva, with a maximal diameter of 30.2 mm. Echocardiographic findings revealed an abnormal aortic valve morphology characterized by asymmetric cusp motion and eccentric systolic opening, accompanied by aortic regurgitation. Severe circumferential dilation of the aortic root, ascending thoracic aorta, and aortic arch, without evidence of dissection or rupture, was confirmed on computed tomography angiography and intra-operative transesophageal echocardiography. Hence, a diagnosis of a non-dissecting fusiform TAA was made. The clinical signs resolved completely after cholecystectomy, and the dog remained clinically stable for >200 days without specific treatment for the aortopathy. This is a rare case of an incidentally diagnosed TAA in a dog with aortic valve abnormality. This case indicates that canine TAA may be under-recognized and emphasizes the importance of advanced imaging modalities for identifying TAA in dogs.