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Despite being an unusual finding (Treggiari et al., 2015), ruling heart base tumours in or out is a relatively common indication for echocardiography at the practice level.
Intracardiac masses are strongly associated with cancer in other parts of the body (particularly the spleen), but heart base tumours or masses within the pericardium can often appear in isolation.
Dogs with heart base masses can frequently be asymptomatic. Where symptoms do occur, this may be secondary to an accompanying pericardial effusion. An unexplained pericardial effusion should elicit a search for a heart base tumour or mass within the pericardium, and pericardiecomy has been shown to be particularly successful in such cases.
Above: With the left ventricle above and right ventricle below, could this dog’s effusion be explained by the mass adhered to the free wall?
Other symptoms can be caused by pressure from a large tumour pushing against the heart or major blood vessels, resulting in congestive heart failure and ascites. Arrythmias are also associated with cardiac tumours.
Brachycephalic breeds, particularly Boxers, appear to exhibit a predisposition to aortic body tumours according to the literature. Chemodectoma occur in the wall of the ascending aortic at the level of the heart base, while paraganglioma tumours are located within the atria along the root of the great vessels (Treggiari et al., 2015). While I have seen plenty of Boxers with problems related to their aorta (particularly subaortic stenosis), I have yet to encounter an aortic body tumour – let me know if you have any examples!
Cardiac tumours are particularly rare in cats but, when they do occur, they tend to be malignant.
Echocardiography has 100% sensitivity for detection of cardiac tumours, provided a thorough search is performed from all available imaging windows. Look not just for the tumour itself but also associated signs (effusions, unexplained arrhythmias, unexplained congestive heart failure and ascites). While appearance and location on echo can give some indication of what type of tumour you may be facing, you will need to use other methods to confirm.
Common types of heart base tumour:
Treggiari, E., Pedro, B., Dukes-McEwan, J., et al. (2015). A descriptive review of cardiac tumours in dogs and cats. Veterinary and Comparative Oncology, 15(2):273-288.