Asymptomatic Giant Right Atrial Aneurysm

Abstract

A 5-year-old asymptomatic boy was found incidentally, on a chest radiograph, to have gross cardiomegaly; further evaluation by echocardiography showed a giant right atrial aneurysm. The patient underwent successful surgical reduction of the right atrium, closure of an atrial septal defect, and tricuspid valve repair. These measures were taken to prevent thrombus formation in the right atrium, prevent paradoxical embolism, and lower the risk of atrial arrhythmias. The morphologic features of the resected atrial tissue showed paper-thin wall with a central aneurysm and focal endocardial fibrosis consistent with a diagnosis of idiopathic dilatation of the right atrium. (Tex Heart Inst J 2001; 28:301–3)

Right atrial aneurysm is a rare abnormality. It can be detected at any time between fetal and adult life. Due to its rare occurrence, right atrial aneurysm may easily be confused with other, more common anomalies that lead to right atrial enlargement, such as Ebstein's anomaly. Right atrial aneurysms may be asymptomatic; however, some patients develop arrhythmias or intracavitary thrombi. The optimal therapeutic approach for right atrial aneurysm is controversial. We report the case of an asymptomatic child who was diagnosed with giant right atrial aneurysm and underwent successful surgical treatment.

Case Report

A 5-year-old asymptomatic boy was referred to a pediatric cardiologist for evaluation of a heart murmur detected on routine physical examination. A chest radiograph showed marked cardiomegaly with normal pulmonary vascularity (Fig. 1A). The results of Holter monitoring were reportedly normal. An echocardiogram was interpreted as showing Ebstein's anomaly, and the patient was referred to Mayo Clinic Rochester in July 2000 for surgical repair.

Fig. 1 Chest radiographs show A) cardiomegaly with normal pulmonary vascular markings, and B) normal cardiac size after surgery.

Echocardiography, repeated during the patient's evaluation at our institution, was thought not to indicate Ebstein's anomaly. The tricuspid valve was not displaced. There was mild tricuspid regurgitation and no stenosis. The most important observation was a giant right atrium; the right atrial diameter was 10 cm compared with 2 cm for the left atrium, and the calculated right atrial volume was 398 mL compared with 7 mL for the left atrium (which was somewhat compressed by the right atrium). The right atrial wall was akinetic and without intracavitary thrombus. There was an atrial septal defect with bidirectional shunting. The right ventricle and outflow tract were mildly dilated with preserved systolic function. The left atrium and ventricle were normal.

An electrocardiogram showed sinus rhythm with nonspecific intraventricular conduction delay. Surprisingly, the P wave was normal. We decided to reduce the size of the right atrium surgically and to close the atrial septal defect in order to prevent thrombus formation in the right atrium, prevent paradoxical embolism, and lower the risk of atrial arrhythmias.

During surgery, the giant right atrium was seen, and the right atrial walls were paper-thin. The right ventricle and the tricuspid valve annulus were dilated. The distance between the tricuspid annulus and the leading edge of the anterior valve leaflet appeared to be less than normal. In addition, there was a partial deficiency of tissue of the posterior tricuspid leaflet, and the leaflets did not close fully during systole. The tricuspid cords appeared normal. There was an 8-mm atrial septal defect along the superior aspect of the fossa ovalis (Fig. 2).

Fig. 2 Nondisplaced septal tricuspid leaflet (in contrast with findings of Ebstein's anomaly). The endocardial fibrosis appears white. A forceps has been placed through the atrial septal defect.

The operation included suture closure of the atrial septal defect, tricuspid valve annuloplasty, and an extensive right reduction atrioplasty. Transesophageal echocardiography performed after the repair showed no residual tricuspid regurgitation. Examination of resected atrial tissue showed extreme wall thinning, central aneurysmal formation, and focal endocardial fibrosis consistent with idiopathic dilatation of the right atrium (Fig. 3). The postoperative chest radiograph showed a marked reduction in heart size (Fig. 1B). At a recent 1-year follow-up visit, this patient was asymptomatic and doing well clinically.

Fig. 3 The resected right atrial tissue is paper-thin, with focal endocardial fibrosis and central aneurysmal formation.

Discussion

Giant right atrial aneurysm is a rare condition of unknown origin; whether it is congenital or acquired is controversial. Some prefer to call it idiopathic dilatation of right atrium, while others label it as congenital enlargement of right atrium or right atrial diverticulum. In utero ¹ and familial ² cases have been reported. Bailey ³ 1st reported the condition in 1955, and several case reports followed. ^4–10

Recently, a review was published ¹ of all congenital malformations of the right atrium and coronary sinus reported in the literature from 1955 through 1998. Of the 105 cases in this series, 60 were cases of congenital enlargement of the right atrium. The patients ranged in age from 32 weeks’ gestation to 75 years at the time of diagnosis. Many (48%), like our patient, were asymptomatic. Others presented with arrhythmia, palpitations, chest pain, shortness of breath, and fatigue. Sinus rhythm was observed in 53% of the patients. The major rhythm abnormality was atrial fibrillation or atrial flutter, which occurred in 28% of cases. Other conduction disturbances included pre-excitation, junctional rhythm, atrioventricular block, and incessant supraventricular tachycardia. Patients were at a risk for thrombus formation in the right atrial cavity, which predisposed them to thromboembolic complications such as stroke (paradoxical embolism) and pulmonary embolism. ^11–13 In patients experiencing atrial fibrillation or flutter, thromboemboli may also arise from the left atrium.

In asymptomatic individuals, this cardiac anomaly usually becomes apparent as cardiomegaly on a routine chest radiograph. Various conditions can mimic this entity on a radiograph, including Ebstein's anomaly, pericardial effusion, pericardial cysts, and tumors. ^14,15 Accurate diagnosis is necessary for proper medical and surgical management. Herein lies the importance of recognizing the wide anatomic spectrum of Ebstein's anomaly ¹⁶ and differentiating it from other causes of right atrial enlargement. In cases of right atrial aneurysm, massive dilatation of the right atrium is usually associated with tricuspid annular dilatation and tricuspid regurgitation. In our patient, there also appeared to be a partial deficiency of some tissue of the tricuspid leaflets, which contributed to failure of leaflet coaptation and tricuspid regurgitation.

Patients with arrhythmias have been treated successfully with excision of the right atrial aneurysm, ^17,18 but the arrhythmias may recur after surgical cryoablation. ¹⁹ The best approach to asymptomatic patients has been controversial, with some patients managed surgically and others nonsurgically. Because of the risk of future thromboembolic complications and arrhythmias, we recommend a right reduction atrioplasty and repair of any associated lesions.