HISTORY

A 7-month-old, male German Shepherd dog, weighing 35 kg was referred to the Veterinary Teaching Hospital for evaluation of the cardiovascular system due to exercise intolerance and ascites of four weeks duration. Physical examination revealed a severe abdominal distension and hepatomegaly. The dog had pale mucous membranes and increased capillary refill time. The femoral arterial pulses were weak and the jugular veins appeared distended and pulsatile. On thoracic auscultation the heart sounds were muffled. A 6-lead ECG revealed small amplitude of QRS complexes and slight ST segment elevation. Thoracic radiographs showed a dorsal displacement of the trachea and a globoid cardiac silhouette, suggesting pericardial effusion. Two-dimensional echocardiographic examination revealed a wide echo-free space around the heart, characteristic of pericardial effusion and a fluid-filled single large unilocular mass with a thin and hyperechoic wall in a right caudolateral location. The mass appeared attached to the parietal pericardium by a short pedicle, and a non well-defined hyperechoic structure was seen inside the cyst. Results of a CBC and serum chemistry were within reference range, with the exception of hypoproteinemia (4.4 g/dl). Analysis of peritoneal fluid was typical of a modified transudate. Serosanguineous pericardial fluid, obtained by pericardiocentesis contained 2.8 x 106 RBC/mL and 3.5 x 103 nucleated cells/mL (60% neutrophils, 12% lymphocytes, 24% macrophages and 4% mesothelial cells). A total of 800 mL was collected from the pericardial cavity. Furosemide at a dose of 0.5 mg/kg q 12h was prescribed. Three days later the body condition improved and ascites disappeared. Following right lateral thoracotomy, a single greyish, smooth mass was surgically excised from the pericardial sac. The mass was attached to the apical region of the pericardial sac by a short pedicle. Partial pericardiectomy was performed. A year later the dog remains asymptomatic. Macroscopically, the intrapericardial mass was a unilocular cyst (7.9 cm x 6.5 cm x 5 cm) with a thin wall surrounding a cavity filled with liquid and solid masses of variable size. Microscopic examination of the wall revealed a lining of mesothelial cells on a fibrous connective tissue stroma with papillary projections towards the interior of the cavity. The solid masses were composed of adipose tissue surrounded by fibrous connective tissue which had undergone fat necrosis and metastatic calcification.

DISCUSSION

The gross characteristic of the unilocular cyst and histologic aspect of this clinical case were typical of a congenital pericardial celomic cyst (unilocular, thin-walled cyst lined with mesothelium) reported in humans. Four types of congenital pericardial cysts have been described in humans: celomic, lymphangiomatous, bronchial and teratomatous. Pericardial cysts in dogs are uncommon and to our knowledge a "true" celomic pericardial cyst has not been previously reported in the pericardium of the dog. The possibility of an intrapericardial cyst should be considered in young dogs with clinical signs of cardiac tamponade.