Complicated Lipomatous Hypertrophy of the Interatrial Septum

Abstract

Background

Lipomatous hypertrophy of the interatrial septum (LHIS) is a benign cardiac lesion characterized by excessive fat accumulation in the interatrial septum, often sparing the fossa ovalis. Although typically asymptomatic, severe cases may lead to hemodynamic compromise.

Cases Summary

We report 2 cases of exuberant symptomatic LHIS requiring surgical intervention. The first patient presented with dyspnea and upper extremity swelling, whereas the second had progressive exertional dyspnea. Multimodality imaging confirmed large interatrial septal masses leading to hemodynamic compromise. Both underwent successful surgical resection with histopathologic confirmation of benign adipose tissue. These cases highlight the importance of multimodality imaging in diagnosing and assessing LHIS in ambiguous and symptomatic cases.

Conclusions

LHIS is an often underrecognized entity that can lead to significant hemodynamic complications. Comprehensive imaging and timely surgical intervention are key to optimal management in severe cases.

Graphical Abstract

Lipomatous hypertrophy of the interatrial septum (LHIS) is a benign cardiac lesion characterized by the accumulation of adipose tissue in the interatrial septum.¹ It is a rare but increasingly recognized entity with an incidence estimated to be ranging from 1% to 8%.² LHIS has been associated with age, obesity, female sex, and pulmonary emphysema.^3,4 Although it is typically asymptomatic and discovered incidentally in most cases, LHIS has been linked to atrial arrhythmias, including atrial fibrillation and premature atrial contractions, and conduction disturbances.⁵ Moreover, cases with protrusion or significant thickening may result in superior vena cava (SVC) or right atrial (RA) inflow obstruction, leading to symptoms of venous congestion and, in some cases, SVC syndrome.^6,7

Take-Home Messages

• •LHIS should be considered in the differential of lipomatous cardiac masses, particularly in patients with risk factors.
• •Progressive symptoms in known LHIS should prompt reassessment for hemodynamic compromise and need for surgery.
• •Although often asymptomatic, multimodality imaging is essential for accurate diagnosis, surveillance, and/or surgical planning of complicated and ambiguous cases.

LHIS typically spares the fossa ovalis, resulting in a characteristic dumbbell shape on imaging.⁴ However, diagnosing LHIS can sometimes be challenging because of limited awareness of the condition, occasional atypical presentations, and its potential to mimic other cardiac masses. Although echocardiography, particularly transesophageal echocardiography (TEE), can often detect septal thickening and fossa ovalis sparing, a definitive diagnosis may sometimes require advanced imaging modalities such as cardiac computed tomography (CT) or cardiac magnetic resonance (CMR), particularly in ambiguous or symptomatic cases.^8,9

We hereby present 2 cases of symptomatic, exuberant LHIS leading to hemodynamic compromise, both of whom required surgical intervention. These cases highlight the role of multimodality imaging in confirming the diagnosis, resolving diagnostic uncertainty, surveillance, evaluating nearby structures, and guiding surgical planning.

Case 1

A 71-year-old man presented with several months of progressive dyspnea, particularly at rest and when lying supine. He also reported new-onset fatigue, diaphoresis, and bilateral upper extremity swelling. His vital signs were within normal limits, and physical examination was notable only for mild upper extremity edema.

Medical history was significant for infrarenal abdominal aortic aneurysm, coronary artery disease, hypertension, dyslipidemia, chronic kidney disease, and a long-standing history of smoking. Given his smoking history, he was referred to an oncologist, where a chest CT scan was performed, which identified a lipomatous mass surrounding the SVC and causing severe stenosis. He was referred to a cardiologist for further evaluation.

His electrocardiogram showed premature atrial complexes with ectopic atrial bradycardia. Transthoracic echocardiography (TTE) revealed a large, protruding RA mass along with increased interatrial septal thickness (17 mm) (Figure 1A). Left and right ventricular systolic functions were preserved. TEE confirmed the presence of a large RA mass nearly occluding the SVC (Video 1) with partially defined borders (Figure 1B). Given the diagnostic uncertainty, CMR was performed, which confirmed a well-circumscribed, 52.4- × 50.8-mm mass occupying much of the right atrium and causing significant SVC obstruction, with a minimal SVC diameter of 6.2 × 7.2 mm. The mass was well defined, demonstrating separation from pericardial fat, with sparing of the fossa ovalis. T1-weighted imaging showed a hyperintense signal, with suppression on fat saturation sequences, consistent with a severe form of LHIS. The mass was hypoperfused on first-pass perfusion imaging, had no evidence of fibrosis on delayed-enhancement images, and demonstrated no invasion of adjacent cardiac structures. Left heart catheterization with an attempted biopsy of the mass was performed but yielded insufficient tissue for histopathologic analysis. Considering the hemodynamically significant compression, surgical resection was pursued. Preoperative CT angiography demonstrated the classic dumbbell-shaped morphology of LHIS, with an exuberant superior extension (75 × 55 × 49 mm) resulting in distal SVC compression, with no local invasion or venous collaterals noted (Figures 1C and 1D). The patient underwent median sternotomy with resection of the interatrial septal mass and SVC reconstruction. Histopathologic analysis confirmed mature adipose tissue without malignant features. His postoperative course was uneventful, and he was monitored in the cardiovascular intensive care unit before being discharged on daily aspirin.

Figure 1.

Case 1: Composite Multimodality Cardiac Imaging During Work-Up for Lipomatous Hypertrophy of the Interatrial Septum

(A) Apical 4-chamber view on transthoracic echocardiography demonstrating a severely hypertrophied IAS, contiguous with a right atrial mass measuring 3.3 cm in diameter (red asterisk). (B) Bicaval view on transesophageal echocardiography showing a large right atrial mass arising from the IAS, sparing the fossa ovalis, measuring 5.2 × 5.0 cm and causing narrowing and obstruction of the SVC inflow to the RA. (C and D) Preoperative cardiac computed tomography sagittal (C) and coronal (D) slices demonstrating the anatomic relationship of the RA mass arising from the IAS, with neighboring cardiac structures and vessels (highlighted). IAS = interatrial septum; IVC = inferior vena cava; LA = left atrium; LV = left ventricle; RA = right atrium; RPA = right pulmonary artery; RV = right ventricle; SVC = superior vena cava.

Case 2

This is the case of a 58-year-old man with a history of diabetes mellitus, hyperlipidemia, and sleep apnea. He has systemic lipomatous syndrome, with multiple previous large lipomas, primarily in the abdomen, some of which have been partially resected. The patient was first diagnosed with a cardiac mass around 10 years ago when it was already of moderate size. He had been under serial follow-up with echocardiography and CMR, which showed gradual enlargement of the lesion over time. At his last follow-up 2 years prior, he was asymptomatic except for mild exertional dyspnea, and conservative management was recommended.

The patient presented with increasing fatigue and exertional shortness of breath but denied chest pain, orthopnea, palpitations, or other cardiac symptoms. Physical examination was grossly normal, with no signs of heart failure or venous congestion. A prior CMR showed a well-defined 79- × 50-mm mass arising from the interatrial septum, with increased signals on black blood contrast imaging (Figure 2B) and T2-weighted sequences. The mass displayed complete suppression on fat-suppressed sequences (Figure 2C) and showed no enhancement on delayed imaging (Figure 2D), consistent with fatty tissue. It caused mild external compression of the adjacent SVC and inferior vena cava (IVC) at the cavoatrial junction in the right atrium. In view of his worsening symptoms, he underwent TTE, which showed the large RA mass protruding into the right atrial cavity and abutting the right ventricular inflow (Figure 2A). The IVC, however, was normal in caliber, and the tricuspid valve was intact on chest CT (Figures 2E and 2F); the size of his mass has increased compared with prior imaging and the patient's symptoms worsened. Hence, the patient was referred for surgical resection. Intraoperative findings show a well-circumscribed LHIS that extended to the interspace between the aorta and SVC and penetrated through the dome of the right and left atrium; it also compressed the IVC and extended through the diaphragm. The mass was successfully excised, and he underwent complex reconstruction of the dome of the left atrium to the lateral wall of the right atrium and interatrial septum with bovine pericardium. Histopathology confirmed benign adipose tissue in all sections and no evidence of malignant cells. The patient was admitted to the cardiovascular intensive care unit where his course was notable for postoperative atrial fibrillation, for which he was started on oral amiodarone. He also developed accelerated junctional rhythm requiring backup pacing. The patient was then transferred to the regular nursing floor and discharged without further complications.

Figure 2.

Case 2: Composite Imaging Using Transesophageal Echocardiography, Cardiac Magnetic Resonance, and Computed Tomography in the Work-Up of Right Atrial Mass

(A) Midesophageal 4-chamber view demonstrating the mass (red asterisk) occupying the RA cavity and abutting RV inflow. (B-D) Cardiac magnetic resonance black blood contrast imaging sequences showing increased signal intensity of the right atrial mass (B), identical to that of surrounding adipose tissue, demonstrating complete fat suppression (C) on fat-suppressed sequences and exhibiting no LGE on delayed hyperenhancement sequences (D) (first-pass perfusion imaging). (E and F) Preoperative cardiac computed tomography slices demonstrating the anatomic relationship of the right atrial mass arising from the IAS, with neighboring cardiac structures and vessels. AoV = aortic valve; IAS = interatrial septum; LA = left atrium; LGE = late gadolinium enhancement; LV = left ventricle; RA = right atrium; RV = right ventricle; SVC = superior vena cava.

Discussion

LHIS is an increasingly recognized abnormality. In a series of 1292 patients who underwent multislice CT of the thorax, LHIS was diagnosed in 2.2% of cases.⁴ Another study reported a prevalence of 2.8% in 802 patients undergoing CT-positron emission tomography scans, suggesting that LHIS may be more common than previously thought and potentially underrecognized by clinicians.¹⁰ These findings highlight the importance of considering LHIS in the differential diagnosis of patients with lipomatous cardiac masses, even in the absence of typical imaging features. Although LHIS goes unnoticed most of the time, adequate recognition and timely intervention are of increased importance in symptomatic and/or complicated cases. We report 2 cases that highlight the importance of multimodality imaging in the diagnosis, surveillance, and surgical treatment of LHIS with hemodynamic repercussions. TTE is often used for initial screening, and could provide additional information like the presence of septal thickening.¹ TEE could also be used to identify characteristic features and hemodynamic repercussions, and could help differentiate LHIS from other cardiac masses such as myxomas or malignant tumors.^2,9 Although echocardiographic techniques are useful for initial detection in stable asymptomatic patients, further characterization by CT (particularly multislice CT) could provide more detailed images to highlight the characteristic features of LHIS, including its proximity to neighboring cardiac and thoracic structures. CT is highly specific in cases of LHIS, by identifying fatty tissue based on density and effectively narrowing the differential diagnosis in such cases to a few entities such as lipoma or LHIS. This aids in the initial diagnosis, but also in assessing the tumor's size and extent.^4,11 Although CT is often diagnostic, CMR, particularly with fat suppression sequences, is frequently used to further characterize the mass and can provide high-resolution images of the interatrial septum. It is often used in conjunction with other imaging modalities to provide a comprehensive evaluation, especially when there is a discrepancy in findings or when a more detailed anatomic and functional assessment is required.¹² Our described cases underscore this importance. In case 1, advanced cardiac imaging was able to confirm an uncertain diagnosis on echocardiography and provided a detailed roadmap for surgical intervention. In case 2, cardiac CT was instrumental in further characterizing the extent of the tumor in an increasingly symptomatic patient with an established diagnosis of LHIS, ultimately guiding clinical decision-making.

Although LHIS is often asymptomatic and no treatment is usually indicated, surgical intervention may be necessary in symptomatic cases that cannot be managed conservatively like SVC compression, RA inflow obstruction, or severe atrial arrhythmias.^13,14 Surgical treatment was adopted in our cases because of the presence of increasing symptoms and hemodynamic involvement. We therefore emphasize the importance of screening for complications in cardiac masses, which could warrant further testing or intervention. It is also essential to consider other fatty cardiac masses, such as lipomas, in the differential diagnosis. Although the distinction between LHIS and other fat-containing lesions may not always alter clinical management, recognizing the characteristic features of LHIS can aid in diagnosis and guide appropriate surveillance strategies; in symptomatic cases requiring surgical intervention, resection is typically pursued regardless of the specific pathology. Case 2 is a patient with a diagnosed systemic lipomatous syndrome and a history of multiple subcutaneous and retroperitoneal lipoma resections. LHIS was presumably one of the lipomatous manifestations of his genetic systemic disease. To our knowledge, only 1 case in the literature, reported by Takayama et al,¹⁵ has described LHIS as a possible manifestation of a broader lipomatous disorder in a patient with LHIS combined with numerous subcutaneous nodules.

Conclusions

LHIS is often underdiagnosed and can, in some cases, lead to discernible complications. Our cases underscore the importance of multimodality imaging for accurate diagnosis, surveillance, and treatment planning in symptomatic or complicated cases. A comprehensive approach is therefore encouraged for greater diagnostic accuracy in cases of diagnostic uncertainty or arising complications. Surgical resection should be considered in patients with progressive symptoms and hemodynamic compromise.

Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Appendix

Video 1

Transesophageal Echocardiography Showing Superior Vena Cava Compression and Inflow Obstruction