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Clinical Observations |
Cardiovascular MR Research Centre, Prince Charles Hospital, Rode Rd., Chermside, Brisbane, QLD Q4032, Australia.
Received June 3, 2004;
accepted after revision March 2, 2005.
Address correspondence to R. I. vanden Driesen.
Abstract
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CONCLUSION. Cardiac amyloidosis is a common cause of infiltrative heart disease. The combination of subtle widespread heterogeneous myocardial enhancement on delayed postcontrast inversion recovery T1-weighted images, which may initially be dismissed as a technical error, with ancillary features of restrictive cardiac disease is highly suggestive of cardiac amyloidosis.
Keywords: cardiac amyloidosis • cardiac imaging • cardiomyopathy • heart • MRI
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Amyloidosis is the most common cause of restrictive cardiomyopathy outside the tropics. Cardiac injury occurs due to the widespread interstitial deposition of proteinaceous material throughout the myocardium that causes pressure atrophy of adjacent myocardial fibers. Intramural deposition within coronary arteries leads to vessel wall thickening, luminal narrowing, and potentially arterial occlusion. Over time, these changes result in ventricular (and atrial) wall thickening and reduced ventricular wall compliance, impairment of diastolic filling, and eventual diastolic heart failure [1].
Differentiation of amyloidosis from other forms of restrictive cardiomyopathy, such as hypertrophic cardiomyopathy, sarcoidosis, or infiltrative lymphoma, is important for selection of appropriate treatment options.
MR appearances of restrictive cardiomyopathies as a group have been well documented. Findings are similar to those of echocardiography including concentric thickening of the left ventricular wall, reduced systolic function with diminished ejection fraction, restriction of diastolic filling, and enlargement of atria without associated ventricular enlargement. The reduced ejection fraction is often useful to differentiate restrictive cardiomyopathies from hypertrophic cardiomyopathies, which often are associated with a normal or even increased ejection fraction [3-7].
Descriptions in the literature of more specific MRI features related to cardiac amyloid infiltration are limited. The most common observation has been a diffuse decrease in signal intensity on T1- and T2-weighted images, although this often needs to be formally measured in a region of interest and may not be apparent on simple viewing of images. Patchy areas of enhancement in the myocardium after IV gadolinium administration have also been described [3, 8].
We aim to describe a pattern of myocardial enhancement common to a number of patients referred to our unit for clinical workup who were subsequently confirmed to have cardiac amyloidosis. We believe this pattern is relatively specific for cardiac amyloid, particularly when the other features of restrictive cardiac disease are present.
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Delayed enhancement imaging was performed in the same slice locations using a segmented inversion recovery fast gradient-echo sequence with the following parameters: 4.8/1.3; flip angle, 20°; receiver bandwidth, ± 31.25 kHz; field of view, 35 cm; slice thickness, 8 mm; slice gap, 2 mm; acquisition matrix, 256 x 160; and number of averages, 2. ECG gating with k-space segmentation of 24 views per segment was used. Images were acquired 8-15 min after administration of 0.2 mmol/kg of gadolinium diethylenetriamine pentaacetic acid, using an inversion time of 200-250 msec. This imaging sequence requires the selection of an appropriate inversion time to null the signal from normal myocardium. As the time delay between contrast administration and imaging increases, the inversion time must be increased accordingly. This pulse sequence was also performed in four patients before gadolinium administration. Double and triple inversion recovery images were acquired in four patients. All imaging sequences were acquired at end expiration.
MRI Analysis and Interpretation
Quantitative measures of left ventricular function were derived from the
short-axis SSFP images using software (MASS, Medis) on a workstation
(Advantage Windows, GE Healthcare). The standard technique of manually tracing
the contours of the ventricular borders with a trackball cursor and then
applying Simpson's rule was used to derive measures of left ventricular mass,
end-diastolic volume, and end-systolic volume, from which stroke volume and
ejection fraction were automatically calculated. Images were interpreted
independently by two radiologists with training and experience in cardiac
MRI.
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In all patients, there was widespread enhancement of the thickened myocardium on delayed postcontrast inversion recovery T1-weighted gradient-echo images. The pattern of enhancement was heterogeneous in most patients, although almost all of the myocardium showed some degree of involvement. Subendocardial enhancement was present in some cases but was not the predominant pattern (Figs. 2A, 2B and 3A, 3B).
The same T1-weighted pulse sequence was performed both before and after IV contrast administration in four cases to confirm that the observed changes in myocardial signal represented true enhancement (Fig. 4A, 4B). In all of these cases, there was no increase in myocardial signal detected before the administration of gadolinium. Double and triple inversion recovery sequences were unremarkable.
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On delayed postcontrast images acquired 8-15 min after IV gadolinium administration, a definite widespread heterogeneous pattern of increased signal on inversion recovery T1-weighted images was observed throughout the myocardium in six of the seven patients. Similar changes were seen in the seventh patient, but they were more subtle. This pattern differs from common patterns of enhancement associated with other entities such as ischemic infarction, which usually shows intense subendocardial or transmural enhancement; infiltrative diseases such as sarcoidosis or lymphoma, in which enhancement is often focal; and interstitial fibrosis, which may show longitudinal striae of mid wall enhancement. The degree of enhancement was considerably less than that seen with replacement fibrosis of myocardial infarction [9].
The delayed enhancement imaging sequence depends on the selection of an appropriate inversion time to null the signal from normal myocardium. Typically, at 8-15 min after injection, this is between 200 and 250 msec. In every one of our patients, the entire myocardium enhanced to some extent. Therefore, even with the correct inversion time selected, suppression of signal from normal myocardium could not be achieved. This finding may be initially misinterpreted as a technical issue, preventing recognition of the diffuse disease process.
As we noted in the Results section, pleural and pericardial effusions were present in six patients. Although the presence of effusions may be explained by the associated impairment of cardiac function, it should also be noted that amyloidosis itself is often a primary cause of both pleural and pericardial effusions [10].
So far, we have observed only a limited number of patients, all of whom have been at an advanced stage in their disease with significant impairment of cardiac function. It remains to be determined whether myocardial changes can be observed earlier in the disease process.
In conclusion, we consider the combination of widespread heterogeneous myocardial enhancement with other supporting features of infiltrative myocardial disease to be relatively specific for cardiac amyloidosis. The enhancement pattern may be incorrectly dismissed as a technical failure of myocardial signal suppression on the inversion recovery gradient-echo T1-weighted pulse sequence commonly used for delayed enhancement imaging. Amyloidosis should be considered whenever there is difficulty suppressing signal from the myocardium on delayed enhancement images with standard inversion times.
Further assessment and correlation of these findings with greater patient numbers may determine more specific MRI features of amyloid cardiomyopathy, with more accurate estimation of the sensitivity and specificity of these findings.
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