Noninvasive Characterization of Left Atrial Mass
A 75-year-old woman presented for workup of a systolic murmur and recurring episodes of atrial fibrillation. Transthoracic and transesophageal echocardiography revealed biatrial dilatation, severe mitral valve stenosis, and a large left atrial mass attached to the atrial septum (IAS) (Figure 1). Thus, the patient was referred to us for presurgical cardiac catheterization. Coronary angiography ruled out coronary artery disease and demonstrated atypical vascularization of the left atrium, indicating additional perfusion and leaking of contrast media in the area where the mass was attached to the IAS (Figure 2). Movie I and Movie II show fully animated versions of Figure 1 and Figure 2, respectively. From the results of echocardiography and cardiac catheterization, the most likely diagnosis appeared to be left atrial myxoma. In patients with mitral valve stenosis, however, chronic atrial thrombus remains an important differential diagnosis. Therefore, the patient underwent cardiovascular MRI (CMR) for additional noninvasive characterization of the left atrial mass.
CMR was performed with a 1.5-T Magnetom Sonata (Siemens Medical Systems). Fast-gradient-echo steady-state free-precession (SSFP) cine and single-shot imaging confirmed the echo findings of biatrial dilatation, mitral valve stenosis (mitral valve area, 0.8 cm2), and left atrial mass attached to the IAS (Figure 3, top, and Movie III). The mass was measured as 40×50 mm. Interestingly, gradient-echo perfusion imaging did not reveal any blood flow in the atrial mass during the first pass of contrast agent, which is atypical for myxoma (left middle panel of Figure 3). In addition, the T1 relaxation time of the atrial mass was not shortened after administration of gadolinium; thus, the inversion time required to null the mass was 600 ms compared with 300 ms needed to null normal myocardium (see right middle row and bottom panels of Figure 3). This is also atypical for myxoma but a frequent finding in the setting of intracardiac thrombus. Consequently, the left atrial mass was ruled to be thrombus by CMR.
A few days later, the mass was removed during mitral valve replacement surgery. Histopathological evaluation revealed a massive thrombus (45×55×70 mm) that formed on top of a very small preexisting left atrial myxoma, most probably because of impaired atrial flow in the setting of severe mitral valve stenosis. This finding explains not only the results of CMR but also the septal attachment of the mass and the atrial vascularization indicated by coronary angiography.
Despite the fact that transesophageal echocardiography is and remains the gold standard for noninvasive assessment of intracardiac structures, the present case demonstrates how CMR can add diagnostic information because of its unique capability of noninvasive tissue characterization if performed in addition to echocardiography.
The online-only Data Supplement, which contains Movie I, Movie II, and Movie III, is available at http://circ.ahajournals.org/cgi/content/full/113/2/e19/DC1.