Giant Interatrial Septal Aneurysm Mimicking a Left Atrial Mass

Abstract

Interatrial septal aneurysm (IASA) consists of redundant atrial septal tissue, which bulges into either the left or the right atrium. The clinical implications of this entity are not entirely clear; however, if it is associated with other cardiac abnormalities such as patent foramen ovale and atrial septal defects. It may assume significance by increasing the risk of cardioembolic events such as stroke. We present a case of an individual with giant IASA detected by transesophageal echocardiography, which was mimicking a left atrial mass on transthoracic echocardiography. This case emphasizes the superiority of transesophageal imaging over transthoracic echocardiography for this clinical entity.

INTRODUCTION

Interatrial septal aneurysm (IASA) along with atrial septal defect and patent foramen ovale are congenital anomalies which are encountered often in the adult patient. With improvement in two dimensional echocardiography and the increasing usage of transesophageal echocardiography, IASA is no longer considered a rare clinical entity. Early detection may prevent hemodynamic and thromboembolic sequelae.

CASE REPORT

A 41-year old male patient was referred to our institution by his primary care physician for transthoracic echocardiography to evaluate his hypertensive heart disease. The transthoracic echocardiography (TTE) showed a large mass measuring 1.4 × 1.4 cm in the left atrium that could represent a thrombus or myxoma [Figure 1]. The patient was asymptomatic and his past medical history was unremarkable except for hypertension. Clinical and laboratory examinations demonstrated no abnormality. Computed tomographic (CT) scan of the chest and heart with intravenous contrast did not show any cardiac tumor. TEE was then done and it showed a giant IASA bulging into the left atrium and mimicking a left atrial mass [Figure 2]. The patient had not had stroke or other cardio embolic phenomenon; therefore no further interventions were undertaken other than starting aspirin.

Figure 1.

Transthoracic echocardiography showed a large mass (white arrow) measuring 1.4 × 1.4 cm in the left atrium that could represent a thrombus or myxoma

Figure 2.

Transesophageal echo showing interatrial septal aneurysm (white arrow)

DISCUSSION

IASA is a congenital malformation of the atrial septum that may occur as an isolated abnormality or in association with various cardiac defects, such as patent foramen ovale (PFO), atrial septal defect (ASD), and mitral valve prolapse or connective tissue diseases.[1,2] Its prevalence varies depending on the diagnostic method used but with the widespread use of echocardiography, IASA has become an increasingly recognized entity. Rusznak, et al.,[3] concluded that IASA is detected in 8% of the patients who undergo TEE; it is associated with PFO in 25% of cases and with ASD in 22.5% of cases. The diagnosis of IASA is very important to prevent various complications and in differentiating it from an intracardiac mass-like myxoma which will have implications on choice of therapy. Nongated chest CT may be unable to distinguish ASA from intracardiac mass like in our case and in such cases, TEE should provide clarification.

However, when echocardiographic evaluation is suboptimal, ECG-gated cardiac MRI and ECG-gated cardiac 64-multidetector CT scan are useful alternative modalities of diagnosis.[4] TEE has to be regarded the imaging modality of choice for initial evaluation of this lesion as various studies have shown that a significant number of patients with IASA detected on TEE were not diagnosed on TTE.[5,6] Also as in our case TEE can help distinguishing IASA from an atrial mass, which may not be feasible on TTE images.

Although IASA are usually found incidentally as in our case, they can have clinical consequences, such as cardiac thrombo-embolic events,[7] right to left shunt across a PFO or ASD, or can mimic a left or right atrial tumor. An annual stroke rate of 3.8% among patients with IASA and PFO compared with 1.05% among those without these anomalies was found in a systematic review of patients with cryptogenic stroke.[8] This study implied a possible increased risk of recurrent stroke in patients with ASA and PFO.

Observations have also been made regarding prevalence of atrial arrhythmias in patients with IASA but no definite associations have been established in this regard. A study by Hanley, et al.,[9] noted atrial arrhythmias in 25% of patients with IASA.[9] In another multicenter study of 195 patients atrial tachycardia was found in 24% of patients with IASA and 14% of patients had atrial fibrillation.[6]

Management options for atrial septal aneurysm vary according to the clinical scenario with interventions ranging from just observation in asymptomatic individuals to ablation by surgical or catheter interventions in patients at high risk of stroke.[10,11]