Pulmonary Embolism and Right Heart Failure Associated With Lipomatous Atrial Septal Hypertrophy: A Case Report

Introduction

Lipomatous hypertrophy of the interatrial septum, also known as lipomatous atrial septal hypertrophy (LASH), is a benign but uncommon condition characterized by excessive accumulation of adipose tissue within the interatrial septum [1]. The true prevalence of LASH remains unknown; however, increased utilization of cardiac imaging in clinical practice has led to more frequent identification. Although most cases remain asymptomatic, rare presentations with symptoms of superior vena cava (SVC) obstruction have been reported [2]. LASH causing SVC obstruction with subsequent pulmonary embolism is rare. We describe a 75-year-old woman who presented with bilateral pulmonary emboli and an incidental finding of LASH associated with SVC and right atrial obstruction. We also review current literature addressing its clinical presentation, diagnostic imaging modalities, and general management principles.

Case Report

A 75-year-old woman with a history of chronic obstructive pulmonary disease, hypertension, and tobacco use presented with exertional dyspnea that had gradually progressed over 12 months; substantial worsening had occurred during the preceding 7 days. Associated symptoms included orthopnea, paroxysmal nocturnal dyspnea, and bilateral lower-extremity edema. No chest pain, cough, or fever was evident. Other than an appendectomy performed several decades earlier, the patient reported no recent surgery, travel, or exposure to sick contacts. She regularly used prescription medications for hypertension (diltiazem and telmisartan) and insomnia (zolpidem), without recent changes; she had no known medication allergies. Her family history was notable for coronary artery disease (father) and lung and cervical cancer (sister). She had discontinued smoking 1 year before presentation and denied other recreational drug use. She had previously worked as a chiropractic therapist and was retired at the time of presentation. Physical examination revealed a temperature of 97.8°F, heart rate of 65 beats/min, blood pressure of 161/80 mmHg, respiratory rate of 22 breaths/min, and oxygen saturation of 98% on room air. Cardiovascular examination demonstrated normal S1 and S2 heart sounds without murmurs, rubs, or gallops. Bilateral 1+ pitting edema of the lower extremities was present, with elevated jugular venous pressure. Respiratory examination revealed normal work of breathing, symmetric air entry bilaterally, and occasional bibasilar crackles.

Laboratory investigations (Table 1) were notable for an elevated D-dimer level of 1.46 μg/mL, with normal hematocrit, white blood cell, and creatinine findings. Chest radiography showed no evidence of pneumonia, and electrocardiography demonstrated normal sinus rhythm without ischemic changes (Figure 1B). Computed tomography pulmonary angiography revealed bilateral pulmonary emboli and intracardiac lipomatosis causing SVC constriction (Figure 2). Lower-extremity venous Doppler ultrasonography results were negative for deep venous thrombosis. Intravenous heparin was initiated and the patient was admitted. Transthoracic echocardiography demonstrated lipomatous hypertrophy of the interatrial septum, with a 5.5×6.2-cm mass located in the superior aspect of the right atrium, compressing the SVC and nearly obliterating the right atrial cavity (Figure 1A). No evidence of a patent foramen ovale, clinically significant valvular disease, or left ventricular dysfunction was identified. These findings led to suspicion that blood flow stasis within the right atrium served as a predisposing factor for thromboembolism. On hospital day 5, the patient underwent coronary angiography with left and right heart catheterization to evaluate possible coronary artery disease. Normal right heart pressures were observed, with stenosis of the left anterior descending and distal right coronary arteries. The patient was discharged on apixaban and scheduled for elective outpatient surgery. One month later, median sternotomy was performed, followed by coronary artery bypass grafting with a left internal mammary artery graft to the left anterior descending artery, a saphenous vein graft to the posterior descending artery, and partial resection of the interatrial septum. Histopathologic examination confirmed lipomatous hypertrophy of the myocardium with focal fibrous scarring; there was no evidence of granulomatous inflammation, vasculitis, or malignancy. The patient tolerated the procedure well and had an uneventful postoperative course. The acute pulmonary embolism was ultimately attributed to sluggish flow and mechanical obstruction within the right atrium secondary to LASH. Apixaban was safely discontinued 3 months after surgery.

Discussion

This case illustrates a unique presentation of LASH and underscores the importance of echocardiography in the evaluation of pulmonary embolism. LASH is characterized by benign but pronounced accumulation of adipose tissue within the interatrial septum. The first case was described by Prior in 1964 [1], and subsequent reports have further characterized this entity. Advanced age and increased body mass index are recognized risk factors; the reported incidence ranges from 1% to 8% [3]. Typically, this nonencapsulated mass exceeds 2 cm in thickness. Histologically, LASH is characterized by adipose tissue accumulation with scattered atypical and fibrotic myocytes [4]. Involvement usually affects the interatrial septum superior and inferior to the fossa ovalis, while sparing the fossa itself. This distinctive distribution produces the characteristic dumbbell-shaped appearance on imaging studies [5]. Although confined to the atrial septum, adipose tissue accumulation may become extensive, leading to suspicion of a malignant neoplasm on imaging examination. Consequently, LASH represents an important differential diagnosis in the evaluation of an atrial mass. Rarely, extension into the right atrium may cause SVC obstruction, as observed in the present case.

The majority of patients with LASH remain asymptomatic and do not require intervention. In rare instances, cardiac arrhythmias and symptoms of congestive heart failure may develop when the lesion enlarges sufficiently to obstruct SVC flow. The mechanism underlying arrhythmia in LASH is hypothesized to involve disruption of atrial myocyte activity, given that adipose infiltration may lead to myocyte fibrosis and impaired electrical conduction [6,7]. Mechanical obstruction of the vena cava or pulmonary veins arising from atrial extension of LASH may also precipitate congestive heart failure manifestations, as demonstrated in this case. Venous obstruction and flow stasis leading to thromboembolism have been reported in association with atrial myxoma [8]; however, pulmonary embolism resulting from LASH through a similar mechanism remains rare. Cheezum et al described an 84-year-old woman with LASH who displayed SVC syndrome [9]. A similar report involved a 65-year-old woman who presented with chest pain [10]. Both patients underwent surgical exploration and resection; however, neither case was complicated by pulmonary embolism, making the present report unique.

Several imaging modalities have been used for the diagnosis of LASH, including transthoracic echocardiography, transesophageal echocardiography, computed tomography, and cardiac magnetic resonance imaging. Two-dimensional echocardiography (transthoracic or transesophageal) is the imaging modality of choice due to its lower cost and wide availability [11]. Regardless of the imaging technique selected, the characteristic dumbbell-shaped appearance of the interatrial septum is often sufficient to establish the diagnosis. In equivocal cases, computed tomography or cardiac magnetic resonance imaging may be used to confirm the fatty composition of the mass [7].

Considering population aging and the expanding use of noninvasive imaging, LASH detection is expected to increase. Other benign and malignant cardiac masses, including lymphoma, myxoma, metastases, and fibroelastoma, represent important differential diagnoses and should be considered during evaluation of a cardiac mass. Accurate identification of LASH is essential due to its benign nature and suitability for expectant management; other cardiac tumors often require more invasive therapeutic approaches.

Conclusions

LASH is a benign adipose tissue mass that remains asymptomatic in most individuals. Its characteristic appearance on echocardiography allows distinction from other cardiac masses. In rare instances, enlargement may occur to a degree sufficient to impede SVC flow. Pulmonary embolism resulting from LASH-induced SVC obstruction is an uncommon but possible complication. Recognition of its clinical presentation, diagnostic features, and management is important because increasing echocardiography use is expected to lead to more frequent identification. This case supports consideration of echocardiography as a routine evaluation for patients with pulmonary embolism.