Lipomatous Atrial Septal Hypertrophy, an Unexpected Giant Interatrial Mass: A Case Report and Literature Review

Abstract

Lipomatous atrial septal hypertrophy (LASH) is a histological cardiac benign lesion finding with high prevalence in healthy population, usually detected during imaging procedures for other indications. Nevertheless, it could become clinically significant if it compromises venous return and diastolic left ventricular filling, up to becoming an anatomical substrate for atrial tachyarrhythmias. We present a case of LASH diagnosed in a 54-year-old female patient admitted to our emergency department after ground fall and collateral finding of positive blood cultures leading to transesophageal echocardiography. A giant mass involving the interatrial septum was observed, in the absence of primitive neoplasia evidence after performing a total-body computed tomography scan and abdominal echography. No signs or symptoms of pulmonary venous congestion were observed, and no relevant tachyarrhythmias were detected at continuous electrocardiogram monitoring during the hospitalization period.

INTRODUCTION

Lipomatous atrial septal hypertrophy (LASH) is a histological cardiac benign mass characterized by fatty tissue deposition within the interatrial septum with a thickness increase of up to > 20 mm, first described in 1964.[1] Its prevalence ranges from 2% (in patients undergoing cardiac tomography) to 8%–10% when detected by transesophageal echocardiography (TEE) which appears the most sensitive technique to identify the mass.[2,3] LASH typically appears as a hyperechogenic mass surrounding the fossa ovalis (FO) (usually spared) and involving the left or right atrial side of the inter-atrial septum (IAS). It could also be associated with the septal aneurysm or patent foramen ovale (PFO)-related shunt which could be excluded using color Doppler imaging and/or bubble test. LASH entity could range from mild IAS thickening to giant interatrial mass, exceeding centimeters in transverse diameter and obstructing left ventricular (LV) diastole and/or pulmonary venous return. Cardiac magnetic resonance (CMR) represents a valuable alternative in diagnosing this type of lesion. T1- and T2-weighted imaging (including fat suppression) and gadolinium-based contrast sequences are able to identify the nature of the mass which appears: (1) hyperintense at T1-weighted (T1w) sequence, (2) hypointense at T2w images with fat saturation, and (3) isointense at inversion-recovery gradient-echo late gadolinium enhancement.[4,5] Occasionally, this finding could be also detected by positron emission tomography (PET)-TC fluorodeoxyglucose 18 performed for other indications such as infective endocarditis or suspect neoplasia.[6] LASH usually occurs as collateral finding with excellent prognosis. Rarely, it could become clinically evident through obstruction of the superior vena cava (SVC) ostium or expanding into the right or left atrium and sometimes compromising LV diastolic filling and pulmonary venous return.[7] Furthermore, considering the increasing number of percutaneous cardiac procedures over the last decade, its detection could manifest as an unexpected fence during transseptal approach and its recognition could modify the procedure planning,[8] given that a thick interatrial tissue can reduce catheter maneuverability after entering the left atrium. LASH is also associated with an increased risk of developing atrial arrhythmias, including atrial fibrillation or atrial flutter,[9,10] rarely involving atrioventricular (AV) conduction leading to advanced AV block.[11] Pathogenesis of LASH appears still uncertain. It usually occurs in the elderly age and in obese patients,[12] suggesting a role of adult adipocyte degeneration.[13] It has been postulated an uncorrected folding of the septum primum and septum secundum during septal development in the embryogenic era, leading to mesenchymal cell incarceration and maturation into adipocytes which can significantly lead to septal thickening in the adult age. Differential diagnosis between LASH and malignant primary or secondary masses is mandatory. When an interatrial mass is detected, a comprehensive multimodality imaging approach is recommended, integrating information gathered from TEE, CMR, computed tomography (CT) scan, and PET-TC,[5,14] to obtain information on its extension and tissue characterization, excluding neoplastic origin.

CASE REPORT

We present a case of LASH diagnosed in a 54-year-old female patient admitted to our emergency department after facial and spine injury due to a ground fall although no loss of consciousness was referred. She had a history of surgical resection of rectal polyp, hypertension, major depressive disorder, left eye blindness from birth, and a dental (radicular) granuloma. Blood coltures tests showed an inflammatory state with elevated C-reactive protein and procalcitonin associated with decompensated glycometabolic state (fast glucose up to 600 mg/dL, HbA1c: 13.9%). The patient was hospitalized at the internal medicine unit, where blood cultures were taken during fever peak, and Streptococcus anginosus was detected. For this reason, the patient was referred to our echocardiography laboratory (echo lab) to exclude an infective endocarditis (IE). Transthoracic echocardiography (TTE) showed a concentric LV hypertrophy, compatible with chronic systemic hypertension with a preserved biventricular systolic function and a marked thickening of the interatrial septum. No evidence of IE was found, and cardiac valves appeared free of vegetation. An empiric intravenous antibiotic regimen was started (amoxicillin and clavulanic acid 2 g tid), and after antibiogram result, it was shifted to meropenem 1 g tid. Because of a persistent suspicion of IE, the patient was referred to an echo lab for a second-level imaging technique, and a TEE has been performed. Concentric hypertrophy of the left ventricle was confirmed with no evidence of valvular masses compatible with infective vegetation. Moreover, a strange interatrial septum was observed with pathological thickening and hyperechogenic and a maximum thickness of 22 mm measured in short-axis view [Figure 1 and Video 1]. The FO was spared, with an evident septal aneurysm (type 4 L-R according to Olivares-Reyes classification) without interruptions or interatrial shunts at color Doppler [Figure 2 and Video 2]. Neither obstruction of the SVC ostium nor expanding processes into the right or left atrium were evident. The echocardiographic data suggested a diagnosis of LASH. A total-body CT scan with contrast and a complete abdominal ultrasound scan were performed to exclude active neoplastic processes or cardiac metastatic involvement. CMR was not performed due to the patient’s claustrophobia and lack of strong indications due to a low probability of alternative diagnoses at TEE. No relevant arrhythmias have been registered during the hospitalization period. The patient has been discharged with a main diagnosis of dental abscess-related sepsis associated with glycometabolic decompensation. A complimentary diagnosis of lipomatous atrial septum hypertrophy was added. A therapeutic regimen with oral cephalosporin was prescribed and regular cardiological follow-up has been recommended after discharge.

Figure 1.

2D-TEE mid-esophageal 2D bicaval (111°) view showing the hypertrophied interatrial septum with evident aneurysm of the fossa ovalis. 2D = Two-dimensional, TEE = Transesophageal echocardiography

Figure 2.

2D-3D TEE X-plane view of the interatrial septum with FO aneurism in the absence of evident shunt. 2D = Two-dimensional, 3D = Three-dimensional, FO = Fossa ovalis, TEE = Transesophageal echocardiography

DISCUSSION

The etiology of LASH is unclear: it has been postulated that fat accumulation is due to the embryologic development of the interatrial septum. It is well established that LASH is a macroscopic and histological cardiac benign finding characterized by: (1) massive fatty tissue deposition within the interatrial septum, (2) accidental diagnosis during cardiac imaging investigation performed for other reasons, and (3) good prognosis quoad vitam. The prevalence ranges from 2.2% in patients undergoing multislice CT to approximately 8% in patients referred for TEE.[3] The exclusion of cardiac metastatic involvement from primitive extracardiac tumors or primitive cardiac masses is crucial. TEE is the most sensitive technique to confirm diagnosis. Although it is considered a histologically and clinically benign lesion, physicians should take into account a rare but not negligible association with cardiac arrhythmias (mainly atrial fibrillation) or hemodynamic complications that should be investigated. The main question is: what should we do when a finding like this appears on our echo machine screen? Before responding to this question, we report a summary derived from the literature accounting for five crucial points:

1. LASH is characterized by >2 cm fat deposition in the area of the interatrial septum

2. LASH is composed of mature adipose tissue and brown (fetal) adipose tissue (BAT)

3. LASH may be associated with advanced age and obesity as well as atrial arrhythmias

4. Echocardiography, CT, and magnetic resonance imaging (MRI) are used to diagnose LASH, which has a bilobed appearance

5. LASH may not be a contraindication to percutaneous interventional procedures.

First of all, a multimodality imaging, including echocardiography (TTE and TEE in both two-dimensional [2D]-three-dimensional [3D] modality), CT, and MRI, is mandatory. An appropriate imaging strategy allows to make a correct diagnosis by: (1) measuring the maximum thickness of the interatrial septum that should be >2 cm (cutoff value) and (2) evidencing the pathognomonic dumbbell shape of the lesion. The dumbbell shape is due to a fat accumulation that is cephalad and caudad to the FO, with sparing of the fossa itself. Another reason for using multimodality imaging is that LASH must be included in the differential diagnosis of any type of atrial mass or fat-containing neoplasm. Regarding arrhythmic complications, LASH should be investigated as the cause of paroxysmal atrial fibrillation in otherwise healthy and obese patients. We speculate a potential strong correlation between LASH and atrial arrhythmias. The main question is if this type of lesion could represent a trigger for a higher incidence of AF.[15] Fatty tissue deposition in the atrial septum may contribute to electrical potential dispersion and neo-circuit genesis, leading to any atrial tachyarrhythmias, potentially reversible after surgery. This intriguing link should persuade physicians to screen patients for parossistic atrial fibrillation in the presence of a diagnosis of LASH, to identify the subclinical forms requiring oral anticoagulation in the presence of an increased thromboembolic risk. Furthermore, LASH is typically included in the list of challenges for transseptal puncture, alongside atrial septal aneurysm and previous atrial surgery.

The septum should be crossed through the thin portion of the septum, but LASH may interfere with directing the needle to the FO and require a higher degree of force. In addition, puncturing of the hypertrophied area can reduce the maneuverability of the catheter after entering the left atrium. This may lead to dangerous consequences, sometimes resulting in the pericardial effusion or an intracardiac shunt. About transcatheter closure of atrial septal defects and patent foramen ovale (PFO), a retrospective analysis by Rigatelli et al.[16] examining transcatheter PFO closure in patients with LASH concluded that the procedure may not be contraindicated if it is possible to perform an accurate evaluation of rim thickness with intracardiac echocardiography. Finally, about treatment strategy, usually LASH does not require any intervention because the quoad vitam prognosis is good. Surgical correction must be considered in cases of severe rhythm disorders or severe vena cava obstruction due to an extended infiltration and right atrial protrusion. Although these complications are very rare, both of them may lead to a heart failure picture.

CONCLUSIONS

LASH is characterized by fat deposition in the septum secundum. At echocardiography, LASH is identified by significant (>2 cm) fat infiltration in the area of the septum that spares the FO. Although LASH is considered a histologically benign finding, there is a reported association with atrial arrhythmias, sudden cardiac death, and congestive heart failure that appear to be related to the extent of infiltration and size of the lesion. Multimodality imaging, including echocardiography (TTE and TEE in both 2D-3D modality), CT, and MRI, is mandatory to make a correct diagnosis, excluding primary and secondary neoplasms.

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The authors confirm that written consent for submission and publication of this case report including images and associated text has been obtained from the patient in line with the COPE guidance.

Author contribution

All authors contributed to this work.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published, and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.