Aim A giant aneurysm of the right atrial appendage (ARAA) a rare cardiac anomaly of unknown cause characterized histopathologically by focal thinning of the endocardium, of the myocardium, and by the thinning to the disappearance of the pectinate muscles. Between 1955 and 1998, 60 cases were reported worldwide, later sporadic cases, of which less than 20 were in children. In most cases, the aneurysm of the right atrial appendage is asymptomatic, but it can increase in size associating palpitations, dyspnea, thrombosis with embolic manifestations, supraventricular arrhythmias up to compression of the right ventricle, thus, diagnosis and early treatment are very important.

Material and Method This case shows the importance of excluding less common causes of right atrial dilatation, which could greatly influence the management of the case, thus limiting multiple complications that may occur.

Results A 4-year-old boy, with no significant family history, asymptomatic, was diagnosed with ARAA following the detection of cardiomegaly on a chest X-ray performed for respiratory interference. Prophylactic treatment with Aspenter 4 mg/kg was instituted. During the echocardiographic monitoring, Holter-ECG, and cardiac MRI for 12 months, the patient remained asymptomatic. Anyway, the giant dilatation of the ARAA was compressing the right ventricle generating a mild hypoplasia of the tricuspid annulus, but the family preferred just evaluation.

Conclusions ARAA is a rare congenital anomaly that can progress and cause important complications. The most frequent complications of this malformation are thromboembolic manifestations and supraventricular arrhythmias. Echocardiography and cMRI are effective for diagnosis and follow-up. There is no consensus regarding the indications and timing of the surgical intervention, which is generally performed in the presence of symptoms and/or complications. Thromboembolic prophylaxis is essential until surgery is performed. Although it is an extremely rare anomaly, it is important to recognize and differentiate, especially from Ebstein’s disease, an important cause of right atrial dilatation in the pediatric population.