Lipomatous Metaplasia in Ischemic Cardiomyopathy
A Common but Unappreciated Entity
A 68-year-old man with a 14 year prior history of anterior myocardial infarction was referred for viability assessment. He had established 3-vessel coronary artery disease with a proximally occluded left anterior descending coronary artery. He complained of worsening shortness of breath and diminishing exercise tolerance. Cardiac magnetic resonance imaging demonstrated a nondilated left ventricle with minor aneurysmal transformation that affected the mid-anterior wall and extended into mid- and antero-septum as well as the apex. Gradient (Figure, A) and T1-weighted spin-echo images demonstrated bright signal intensity in the mid-myocardium of the anterior wall (see arrows in Figure, B), which disappeared with fat saturation (see arrows in Figure, C and D). These findings are indicative of lipomatous metaplasia (LM). The term LM describes fat that is present in and seemingly replaces scar tissue in the myocardium. The exact etiology of LM is unknown, but it is not seen in the absence of substitutive myocardial fibrosis. Histological evidence of LM has been found in up to 68%, 24%, and 37% of areas of left ventricular myocardial scars in explanted hearts of patients who underwent transplantation for ischemic heart disease, idiopathic dilated cardiomyopathy, or chronic valvulopathy, respectively.1 Myocardial perfusion imaging (lipohilic myocardial perfusion agents such as tetrofosmin and sestamibi may well be taken up into fat cells) and echocardiography fail to diagnose LM (which accounts for the lack of recognition of this not uncommon entity) with the consequent implications for overestimation of viable myocardium or underestimation of scar size.
Importantly, LM on magnetic resonance imaging must not be mistaken for late enhancement after gadolinium contrast.
The online-only Data Supplement, consisting of movies, is available with this article at http://circ.ahajournals.org/cgi/content/full/116/1/e5/DC1.