Clinical History A 54-year-old male presented with a presumed diagnosis of Ebstein’s anomaly and atrial fibrillation. His past medical history was remarkable due to an exploratory cardiac surgery in his childhood for a suspected cardiac mass, which revealed an enlarged right atrium. A recent comprehensive echocardiogram revealed a severely enlarged right atrium with no obvious finding that would suggest Ebstein’s anomaly.
He was referred for a cardiac magnetic resonance imaging (MRI) for further evaluation of cardiac anatomy and function.
Cardiac MRI demonstrated a markedly enlarged right atrium, measuring 19 x 16 x13 cm at end-systole (Figure 1). The right ventricle and left heart chambers (Figure 1A,B) were displaced laterally and posteriorly by the enlarged right atrium. The location and orientation of the tricuspid valve in relation to the mitral valve were normal with no evidence of apical displacement or tethering to suggest Ebstein's anomaly. There was tricuspid annular dilatation and a resulting eccentric jet of tricuspid regurgitation seen on phase contrast images (Figure 2A,B).
(Click on image to enlarge)
Figure 1(A,B):(A) Four chamber steady-state free precession (SSFP) image demonstrates a markedly enlarged right atrium with displacement of the right ventricle and left heart chambers. Note the normal relation of the mitral (black arrow) and tricuspid valves (white arrow). (B) Short axis SSFP image again demonstrates the markedly enlarged right atrium. RA: Right atrium, RV: Right ventricle, LA: Left atrium, LV: Left ventricle.
Figure 2(A,B):Phase contrast imaging demonstrates an eccentric, anteriorly directed jet of tricuspid regurgitation (arrow) in both the magnitude (A) and phase contrast images (B).
Idiopathic dilatation of the right atrium is a very rare condition of unknown origin and was first reported by Bailey. The partial loss of atrial muscle fibers with progressive atrial enlargement was proposed as the causative mechanism. The clinical presentation varies but is frequently an incidental finding detected on the chest radiography done for routine evaluation or during the evaluation of the atrial fibrillation. Approximately 50% of the patients are asymptomatic at the time of the diagnosis. The common presenting symptoms, when they occur, are shortness of breath (28%), palpitations (17%) and arrhythmia (12%).
Echocardiography, computed tomography (CT) and MRI can all provide important structural and functional information about this condition. MRI can provide high-resolution images of the right atrium and right ventricle as well as quantitative right ventricular volume and systolic function. In addition, alternative pathologies can be excluded. The differential diagnoses of this rare entity include Ebstein’s anomaly, Uhl's anomaly, cardiac tumor, pericardial effusion or pericardial cyst. In our patient, a clinical diagnosis of Ebstein’s anomaly was first considered before the results of echocardiography and MRI were obtained. Surgical reduction of the right atrium can be considered in symptomatic patients although the optimal treatment of this rare condition is not well established.
Bailey CP. Surgery of the heart. Philadelphia: Lea&Febiger Publisher; 1955. P. 413
Gomes S, Wolfenden H, Lambros J. Giant right atrium in an adult: case report of a rare condition. Heart Lung Circ 2012;21:50-52
Kroft LJ, de Roos. A MRI diagnosis of giant right atrium. Am J Roentgenol , 2007;189:94-95
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Suhny Abbara, MD
MGH Department of Radiology
Wilfred Mamuya, MD, PhD
MGH Department of Cardiology