Idiopathic aneurysmal giant right atrial enlargement with thrombus formation.

A 12-year-old boy presented to our outpatient department with progressive dyspnoea and palpitations of 6-month duration. Cardiovascular system examination revealed a short ejection systolic murmur at the left lateral heart border. Chest X-ray showed gross cardiomegaly. Two-dimensional ECHO revealed massive aneurysmal right atrial (RA) enlargement, low-pressure tricuspid regurgitation and dysplastic tricuspid valve with compression of the left atrium (LA) and left ventricle (LV). Cardiac CT showed grossly enlarged RA compressing the LA, LV, right pulmonary artery and right upper lobe pulmonary vein. Initially, the patient refused surgery. On follow-up, a thrombus was seen in the giant RA and the patient agreed to and underwent successful surgery. Absence of pericardium was specifically excluded on cardiac MRI and on surgery. Resected atrial tissue showed wall thinning and focal fibrosis establishing idiopathic dilation of the RA. The patient is on regular follow-up.