Lipomatous hypertrophy of the interatrial septum (LHIAS) is a benign condition characterized by excessive fat deposition within the atrial septum. Fat infiltration is prominent in the cranial and caudal portions of the septum while characteristically sparing the fossa ovalis, creating the pathognomonic 'dumbbell' (bilobed) shape. It is typically discovered incidentally in elderly, obese individuals and those on chronic corticosteroid therapy. Diagnosis is made when septal thickness exceeds 20 mm. Although usually asymptomatic, it can rarely cause supraventricular arrhythmias and superior vena cava syndrome. Autopsy series report a prevalence of 1-8%.
Age Range
50-85
Peak Age
65
Gender
Equal
Prevalence
Common
LHIAS develops from hyperplasia and hypertrophy of fetal brown fat tissue within the interatrial septum. Adipose tissue normally present in the septum accumulates excessively, particularly in the cranial (limbic region) and caudal portions. The fossa ovalis region is spared from fat infiltration due to its fibrous composition, creating the pathognomonic dumbbell shape. Histologically, it contains mature white adipocytes, vacuolated brown fat cells, and entrapped myocardial fibers — hence it is not a true lipoma but a hypertrophic process. Expansion of fatty tissue compresses myocardial fibers and can lead to myocyte degeneration, which explains the mechanism for supraventricular arrhythmias. Obesity, aging, and chronic steroid use are the main predisposing factors that promote fat accumulation. On imaging, fat tissue demonstrates negative HU values on CT and markedly hyperintense signal on T1-weighted MR sequences; signal loss on fat-suppressed sequences confirms the diagnosis.
The dumbbell configuration created by thinning at the fossa ovalis level in the interatrial septum is the pathognomonic finding of lipomatous hypertrophy. Since the fossa ovalis is fibrous in composition, fat deposition skips this region and creates bilobed thickening in the cranial and caudal portions of the septum. This morphology is the most reliable finding for differentiation from lipoma (which may involve the fossa ovalis) and other cardiac masses. It can be seen on CT, MR, and echocardiography, but is best evaluated on MR and CT.
Marked thickening of the interatrial septum with fat density (-30 to -120 HU) is identified. Sparing of the fossa ovalis creates the typical dumbbell configuration. Septal thickness exceeds 20 mm and may sometimes reach 60-70 mm.
Report Sentence
Marked fat-density (-XX HU) thickening of the interatrial septum in a dumbbell configuration with sparing of the fossa ovalis, consistent with lipomatous hypertrophy.
On contrast-enhanced studies, no significant enhancement is observed in the accumulated fat tissue of the septum. While surrounding myocardium enhances normally, fat tissue maintains its avascular character. Rarely, entrapped myocardial islands within the septum may show minimal enhancement.
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No significant enhancement is identified within the fat-density thickening of the interatrial septum on contrast-enhanced imaging.
On T1-weighted sequences, the interatrial septum demonstrates markedly hyperintense signal, isointense to subcutaneous fat. The dumbbell configuration is clearly delineated by the low signal (fibrous tissue) at the fossa ovalis region. Signal intensity is at the same level as subcutaneous and mediastinal fat, confirming intralesional fat content.
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Dumbbell-configured thickening of the interatrial septum demonstrating markedly hyperintense signal isointense to subcutaneous fat on T1-weighted sequence.
On fat-suppressed sequences (STIR, fat-sat T1, Dixon water image), complete signal loss is observed in the interatrial septal lesion. This finding definitively confirms that the lesion contains macroscopic fat. When Dixon technique separates fat and water, the septum appears markedly hyperintense on the fat image and hypointense on the water image.
Report Sentence
Complete signal loss in the interatrial septal lesion on fat-suppressed sequences, confirming macroscopic fat content.
On SSFP cine sequences, a bilobed mass in dumbbell configuration is identified in the interatrial septum. Fat demonstrates intermediate signal on SSFP (not as bright as pure T1-weighted). The 'waist' formation (thinning) at the fossa ovalis level is a diagnostic clue. Atrial wall motion beyond the mass and motionless segments of the septum can be dynamically assessed. In the presence of supraventricular arrhythmia, irregular heart rhythm may create artifacts in the sequence.
Report Sentence
Bilobed structure in dumbbell configuration in the interatrial septum with thinning at the fossa ovalis level on SSFP cine sequences.
On transthoracic echocardiography (TTE), hyperechoic bilobed thickening is identified in the interatrial septum. The dumbbell appearance is seen with thinning at the fossa ovalis region. It is best evaluated in subcostal and apical four-chamber views. Septal thickness can be measured (>20 mm is diagnostic). Transesophageal echocardiography (TEE) provides higher resolution and demonstrates the dumbbell shape more clearly. The lesion has a homogeneous hyperechoic texture without calcification or cystic components.
Report Sentence
Hyperechoic bilobed thickening of the interatrial septum with sparing of the fossa ovalis, suggestive of lipomatous hypertrophy.
On FDG PET-CT, lipomatous hypertrophy of the interatrial septum shows no increased FDG uptake. Benign fat tissue has low metabolic activity and does not mimic a malignant mass. However, entrapped myocardial islands in the septum may show physiological myocardial FDG uptake, which can be misinterpreted as increased activity. Clinical and anatomical correlation is important for differentiating physiological myocardial uptake from pathological uptake.
Report Sentence
No increased metabolic activity is observed in the area of lipomatous hypertrophy of the interatrial septum on FDG PET-CT.
Criteria
Interatrial septal thickness >20 mm, typical dumbbell configuration, septal involvement only, no enhancement
Distinct Features
Most common form. Homogeneous fat signal, smooth contours. Usually asymptomatic and does not require treatment. Septal width rarely reaches 60-70 mm.
Criteria
Fat infiltration of crista terminalis and right atrial free wall in addition to septal thickening, dumbbell configuration usually preserved
Distinct Features
Fat deposition extends beyond the septum to the crista terminalis and right atrial wall. More extensive fat infiltration can create mass effect and contribute to SVC obstruction. Physiological FDG uptake may increase in the crista terminalis region on PET-CT, creating false positivity.
Criteria
Septal thickness >40 mm, massive fat accumulation narrowing the atrial lumen, hemodynamic impact findings (SVC obstruction, restricted atrial septal transit)
Distinct Features
Rare form. Septal thickness may range from 40-70 mm. Can narrow the right atrium and superior vena cava lumen, leading to symptomatic SVC syndrome. More prone to atrial arrhythmias. Surgical resection may rarely be needed. On CT and MR, massive fat accumulation can be confused with a tumor, but fat signal and dumbbell morphology provide differentiation.
Distinguishing Feature
Lipoma is an encapsulated, well-defined fat mass that can also involve the fossa ovalis — does not demonstrate dumbbell configuration. LHIAS is diffuse infiltrative, spares the fossa ovalis, and has dumbbell morphology. Lipoma can originate from any cardiac chamber, while LHIAS is specifically confined to the interatrial septum.
Distinguishing Feature
Myxoma is typically a pedunculated, mobile, heterogeneous mass originating from the fossa ovalis in the left atrium. It shows hyperintense T2, intermediate T1 signal, and contrast enhancement. LHIAS is diffuse fat accumulation in the septum sparing the fossa ovalis, shows no enhancement, and has fat signal. Myxoma causes embolic complications while LHIAS does not carry such risk.
Distinguishing Feature
Cardiac metastasis is typically an irregular-bordered mass with heterogeneous enhancement in the setting of known primary malignancy. It shows high uptake on FDG PET. LHIAS is a homogeneous lesion with fat density showing no contrast or FDG uptake. Metastasis can cause pericardial involvement and effusion while LHIAS does not. Known malignancy history and rapid growth are important clinical clues favoring metastasis.
Distinguishing Feature
Liposarcoma is a malignant tumor containing fat but with heterogeneous, invasive character and contrast enhancement. It has a prominent solid soft tissue component in addition to fat, and these areas show strong enhancement. LHIAS has homogeneous fat content without solid component or enhancement. Liposarcoma shows rapid growth and local invasion while LHIAS is stable.
Urgency
lowManagement
conservativeBiopsy
Not NeededFollow-up
Rutin takip genellikle gerekmez. Semptomatik vakalarda (aritmi, SVC obstrüksiyonu) kardiyoloji takibi önerilir.Lipomatous hypertrophy is a benign condition with no clinical significance in most patients. Diagnosis is typically made with characteristic dumbbell morphology and fat signal on CT or MR; biopsy is not required. Pathognomonic imaging features (dumbbell configuration with sparing of fossa ovalis + fat signal) are sufficient for diagnosis. No treatment or follow-up is needed in asymptomatic cases. In rare symptomatic cases (supraventricular arrhythmia, SVC obstruction), cardiology evaluation and if necessary medical treatment (antiarrhythmic) or very rarely surgical resection may be performed. It is important to correctly differentiate this lesion from malignant cardiac masses (especially liposarcoma).
LHIAS is generally a clinically insignificant incidental finding. However, marked thickening (>2 cm) can cause superior vena cava obstruction, supraventricular arrhythmias, or right heart failure. Definitive diagnosis is made with cardiac MRI or CT. Surgery is rarely needed; surgical excision may be considered for symptomatic and large lesions. Differential diagnosis from cardiac lipomas and malignant tumors is important.