Atypical loculated pericardial effusion with infectious pericarditis mimicking a cardiac mass in a dog: a case report

A 13-year-old, Maltese dog presented with syncope and lethargy. Abdominal ultrasonography demonstrated anechoic peritoneal effusion and hepatic congestion. A focal echogenic round mass compressing the right ventricle and atrium was observed on echocardiography. Cardiac tamponade and right ventricular outflow tract obstruction occurred. On computed tomography, a homogeneous soft-tissue structure compressing the right chamber without contrast enhancement, suspected to be loculated pericardial effusion. During pericardiocentesis, cardiac tamponade was resolved, and irregular pericardial thickening was noted. Pericardial effusion was exudate and gram-positive bacterial colonies were observed on cytology. A diagnosis of fibrinous pericarditis secondary to bacterial infection was established.