Myocarditis MRI


 * Associate Editor(s)-In-Chief: Varun Kumar, M.B.B.S.

Overview
Cardiac MRI findings associated with myocarditis include myocardial inflammation, myocardial edema, capillary leak, and reduced left ventricular function. While the cMRI pattern of gadolinium hyperenhancement in ST segment elevation myocardial infarction is transmural and extends from the endocardium to the epicardium, the patchy, non-segmental hyperenhancement pattern in myocarditis in contrast involves the epicardium and spares the subendocardium.

Indications to Perform Cardiac MRI in the Patient with Suspected Myocarditis
Performance of cardiac MRI is generally indicated in those patients with new or persisting symptoms of chest pain and congestive heart failure, who have evidence of significant myocardial injury, in the absence of or in whom there is a low suspicion of coronary atherosclerosis.

Myocardial Inflammation
Myocardial inflammation associated with myocarditis appears as a high intensity signal with delayed gadolinium hyperenhancement on cardiac MRI (cMRI). . While the cMRI pattern of gadolinium hyperenhancement in ST segment elevation myocardial infarction is transmural and extends from the endocardium to the epicardium, the patchy, non-segmental hyperenhancement pattern in myocarditis in contrast involves the epicardium and spares the subendocardium. The areas of hyperenhancement are often observed in the lateral and inferior territories of the heart.

When used in conjunction with the findings on coronary angiography, cMRI is useful in distinguishing between a diagnosis of myocarditis and myonecrosis associated with myocardial ischemia. Among 79 patients with elevated cardiac biomakrkers who were suspected of having ACS and had normal coronary arteries on coronary angiography, 81% of the patients (including those with preserved ejection fraction) were diagnosed with myocarditis based on cMRI findings.

Myocardial Edema
High T2 signal intensity areas suggests myocardial edema.

Myocardial Scar
Gadolinium-enhanced magnetic resonance imaging (MRI) may also aid in assessing the extent of myocardial scarring (areas of delayed gadolinium enhancement) which is largely confined to the epicardium.

Myocardial Capillary Leak
Myocardial early gadolinium enhancement ratio (ratio between myocardium and skeletal muscle) ≥ 4.0 is suggestive of hyperemia and capillary leakage.

Myocardial Dysfunction
Cardiac MRI can be used to assess for the presence of and severity of myocardial dysfunction associated with myocarditis.

Associated Pericardial Effusion
Cardiac MRI can be used to assess for the presence of and severity of a pericardial effusion associated with myocarditis. The association of a pericardial effusion along with myocarditis is referred to as myopericarditis.

Sensitivity and Specificity
CMR was reported to have a sensitivity of 76%, specificity of 95.5%, and overall diagnostic accuracy of 85% when any-two of the following three sequences were used.
 * Focal and global T2 signal intensity
 * Myocardial global relative enhancement
 * Delayed gadolinium enhancement

Among 21 patients who underwent biopsy of contrast enhanced regions in a series in Germany, histopathologic findings in 19 patients were consistent with myocarditis.