Lipomas are defined as mesenchymal tumors seen at a site where adipose tissue is normally present. True lipomas with encapsulation located in the heart and pericardium are very rare. The incidence of primary heart tumors reported in the autopsy series is between 0.2% and 0.4%8, 9, of which cardiac lipomas account for 8.4%2. Lipomas may occur anywhere in the heart and pericardium, including cardiac valvular leaflets with the predilection of subendocardial origin10–12. The location of cardiac lipomas in the present study also showed predilection within cardiac chambers.
Despite being benign, cardiac lipomas may have a clinical presentation from mild discomfort to even syncope depending on their location and size13. The lipoma within the left ventricle in patient 1 in the present study caused obstruction to the outflow tract and resulted in clinical symptoms similar to those of left ventricular failure. Besides, the presence of infiltration to the myocardium by lipoma may result in severe presentation14. The pericardial lipoma in patient 12 remained silent despite having a giant size. However, the evident chest distress in patient 2 with pericardial lipoma of similar size might be related to diffuse infiltration to the biventricular myocardium.
Most of symptomatic cardiac lipomas can be cured by radical resection. The early detection and accurate diagnosis are of critical significance. Since the clinical application of x-ray imaging tools, the noninvasive detection of cardiac masses, including lipomas, came into realization, which was further facilitated by echocardiography. The advantages of easy availability and convenient operation make echocardiography the preferred screening tool for cardiac masses. Lipomas usually present as homogenous echogenic masses within cardiac chambers or pericardium3, 15. The acoustic characteristics of lipomas can help exclude cardiac malignancies16, 17, but it is difficult to distinguish them from other benign lesions, such as myxoma, by echocardiography18. Fortunately, this has become possible with the application of CT and MRI19, 20.
Lipomas have the same composition as subcutaneous fat and consist of mature adipose tissue. They have the same imaging appearance as that of subcutaneous fat in CT and MRI21. As shown in the present study, most cardiac lipomas can be accurately diagnosed using CT and MRI. On CT, they present as homogenous encapsulated masses with low attenuation (Hounsfield measurement <–50)15, 22. The signal intensity of cardiac lipomas was consistent with that of subcutaneous fat in all MRI sequences, especially the characteristic complete signal loss of the mass in fat suppression sequence23, 24. The application of tissue mapping in cardiac MRI made the diagnosis of lipoma more definitive25, 26. True cardiac lipomas are highly specific in CT and MRI; the main difference is liposarcoma. The size of the lesion and the lipomatous content are reliable discriminators between extracardiac lipomas and liposarcomas27. Thickened or nodular septa, associated nonadipose lesions, prominent foci of high T2 signal, and prominent areas of enhancement are important findings suspicious for liposarcoma28. However, the differentiation between mature cardiac lipomas and well-differentiated liposarcomas may be difficult by imaging29. The information extracted from radiomics may be of value in differentiating between two closely related entities30.
Symptomatic cardiac lipomas were more likely to be resected, while silent lipomas were conservatively treated more often. However, the treatment is highly individualized. Noninvasive cardiac imaging tools including CT and MRI, especially the latter, may be important in clinical decision making regarding cardiac lipomas. Most cardiac lipomas had a broad base attached to the myocardium, while the narrow pedicle attachment, which is best observed with MRI, may indicate radical resection even in asymptomatic patients to prevent potential detachment. On the contrary, cardiac lipomas have no fixed growth pattern. Although most of them show an indolent nature31, aggressive growth, including infiltration into the myocardium, has been reported. Cardiac lipomas may grow to a very large size and infiltrate the myocardium deeply32, 33. In some cases, they are even capable of melting the myocardium and developing cavities in the lipomas that communicate with cardiac chambers, thus having a pseudoaneurysmal appearance34, 35. With cardiac MRI, the infiltrative growth of cardiac lipomas can be clearly depicted for better clinical management36. As shown in patient 2 in the present study, the diffuse myocardial infiltration made the radical removal of the giant pericardial lipoma impossible. Cardiac transplantation was advised for the best solution, though refused by the patient. The imaging findings from MRI in patient 12 also significantly affected clinical decision making. Although the giant pericardial lipoma remained silent, the regional thinning of the ventricular wall, similar to the pseduaneurysmal appearance, raised the suspicion that the lipoma gradually melted the myocardium37, 38. Operative resection was adopted to prevent further growth and potential melting of the ventricular wall.
In addition, cardiac imaging tools are indispensable in the follow-up of cardiac lipomas39. Very rarely, the recurrence of cardiac lipomas has been reported in few cases14, 33. However, no consensus was formed on the follow-up of simple lipomas. A regular visit with cardiac imaging is advocated for all patients undergoing resection. A more frequent follow-up in patient 12 in the present study prompted the earlier discovery of recurrence and a chance to remove the lipoma without transplantation. Patients initially not considered for surgery should be closely followed up using imaging methods because potential infiltrative growth into the myocardium may result in failed resection in the future32. On the contrary, despite no evidence that cardiac lipoma might undergo malignant transformation, mature lipomas and well-differentiated liposarcomas coexist in one heart. A regular review of the tumor would be the best choice, especially using MRI.