Imaging of atrial septum lipoma
During instrumental examinations, atrial septum lipoma (Atrial Septum Lipoma) is visualized as a mass with exceptionally well-defined borders.
A key feature on cardiac CT is the markedly low X-ray attenuation of the tumor tissue (low attenuation). Magnetic resonance imaging (MRI) provides an even more comprehensive picture and allows unambiguous determination of the fatty nature of the tumor:
- On T1-weighted images (T1WI), the mass demonstrates pronounced hyperintensity.
- When using a fat-suppression sequence (STIR - short tau inversion recovery), complete signal suppression from the structure is observed.
- On cine MRI sequences (SSFP - cine-steady-state free precession), the signal intensity is assessed as high or intermediate.
- On post-contrast T1WI, there is a complete absence of contrast agent uptake (no enhancement).
Note: when analyzing MRI scans, attention should be paid to surrounding structures, as an atrial septum lipoma may be associated with a concurrent subpleural lipoma.
Differential diagnosis: Rhabdomyoma
Unlike a lipoma, a rhabdomyoma (Rhabdomyoma) is characterized by a deep location within the myocardial thickness, poor demarcation from surrounding tissues, and typically multiple lesions. An important clinical feature is that the majority of cardiac rhabdomyomas are capable of spontaneous regression.
- Echocardiography: the picture is variable. Tumors may be isoechogenic (making their differentiation from normal myocardium extremely difficult) or hyperechogenic (more common in children and newborns).
- CT: masses show contrast enhancement (enhancing). In multiple involvement, they can mimic diffuse thickening of the myocardial wall.
- MRI: on T1WI, the signal intensity of a rhabdomyoma is completely identical to the adjacent normal myocardium, whereas on T2WI, a relatively increased signal intensity is noted.
Features of cardiac fibroma
A cardiac fibroma (Fibroma) is predominantly a solitary tumor located in the ventricular wall (the left ventricle is affected much more frequently). Clinically, a fibroma manifests as cardiac rhythm disorders (arrhythmias) or the development of congestive heart failure (congestive cardiac failure). The mass may be resectable.
Plain chest radiography may reveal cardiomegaly. CT reveals an infiltrative or well-demarcated mass, usually large (≥ 5 cm). A fibroma is characterized by dystrophic calcification in the form of specific "whorls of calcium" (whorls of calcium) and very poor contrast enhancement.
MRI findings of fibroma:
- The tumor is located intramurally, is poorly vascularized, has clear contours, and is surrounded by a characteristic rim of compressed healthy myocardium.
- Due to its dense fibrous structure, the mass yields a low signal on T1WI and T2WI compared to the intact myocardium.
- On the SSFP sequence, signal intensity is variable; the tumor does not deform on spatial modulation of magnetization sequences (tagged sequences).
- Delayed enhancement (Delayed enhancement) can be peripheral, homogeneous, or heterogeneous. Fibromas without contrast enhancement may visually resemble focal hypertrophic cardiomyopathy (focal HCM).
Papillary fibroelastoma
Papillary fibroelastoma (Papillary Fibroelastoma) ranks second in frequency among benign cardiac tumors. It is almost always a solitary mass. It can form on any endocardial surface, but the most common localization is the atrial aspect of the mitral valve and the aortic aspect of the aortic valve.
Most of these tumors are less than 1 cm in size and are asymptomatic. However, they carry the risk of systemic embolism or sudden cardiac death (due to coronary artery embolism).
The main diagnostic method is echocardiography, where the tumor appears as a small hyperechogenic mass attached to the valve leaflets. On ECG-gated CT (ECG-gated CT), a fibroelastoma may be an incidental finding as a focal low-attenuation mass (low-attenuation mass). Identification on MRI is extremely difficult due to its small size; however, imaging reveals clear contours, an intermediate signal on T1WI and T2WI, and, typically, the absence of delayed enhancement.
Briefly: answers to topical questions
Which benign myocardial tumors must be differentiated from a lipoma?
In the cited sources, lipomatous hypertrophy of the interatrial septum is explicitly indicated as part of the differential diagnosis of a cardiac lipoma. It represents an accumulation of brown adipose tissue leading to thickening of the interatrial septum by more than 2 cm; the oval fossa is typically intact, giving the mass a "dumbbell" shape.
What echocardiographic signs are characteristic of a cardiac lipoma?
The echocardiographic picture of a cardiac lipoma is extremely variable. Other characteristic echocardiographic signs of a lipoma are not specified in the cited sources.
To memorize the MRI picture of a lipoma: "Bright on T1, dark on STIR, does not accumulate contrast." This is the classical triad of diagnostic imaging for adipose tissue.
Class and exam questions
Does a cardiac lipoma accumulate contrast agent?
No, on post-contrast T1-weighted images, contrast enhancement is completely absent.
How to distinguish a lipoma from a fibroma on CT?
A fibroma is prone to massive calcification (the "whorls of calcium" sign) and can be greater than 5 cm in size. A lipoma, however, demonstrates the typical low X-ray attenuation of fat without such calcifications.
Which benign cardiac tumor can undergo spontaneous regression?
Most cardiac rhabdomyomas are prone to spontaneous regression (spontaneous disappearance).
What else to study on this topic
- Mechanisms of fat signal suppression (STIR) in MRI
- Specifics of ECG-gated CT (ECG-gated CT) in valve tumors
- Causes and risks of coronary artery embolism in papillary fibroelastoma
- Differential diagnosis of fibroma and focal hypertrophic cardiomyopathy
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