Right-sided congestive heart failure in a dog because of a primary intracavitary myocardial lymphoma

A 9-year-old female intact Cocker Spaniel was presented with a history of acute-onset dyspnoea and abdominal distension of 3 days' duration. Ultrasonography revealed pleural, peritoneal and pericardial effusions. Abdominal fluid analysis was consistent with a modified transudate. Echocardiography revealed a large, hypoechoic space-occupying mass within the right atrium. The dog was euthanased and the postmortem examination showed a solid, 40 × 35 × 20 mm broad-based mass arising from the right atrial wall and occluding approximately 90% of the right atrial lumen. Histopathology revealed myocardial lymphoma. There were histologically similar, focal nodules in the lung parenchyma without involvement of other extracardiac sites. There was gross and histological evidence of hepatic congestion and marked distension of the caudal vena cava, consistent with secondary right-sided congestive heart failure.

This case highlights the need to consider lymphoma as a differential diagnosis for an intra-atrial mass and as a cause of congestive heart failure in the dog.