The 3D multiplanar reconstruction of the mitral valve was created offline to measure the size of the MAC (Fig. 3). In Figure 3, the size of the MAC that was located more laterally was measured, which was equivalent to the MAC seen in Figure 1. Size measurement by 3D multiplanar reconstruction is useful for echocardiographic follow-up evaluation because caseous MAC is a dynamic lesion that can progress in size.1
MAC is a common manifestation during echocardiographic examinations, especially in the elderly. On the other hand, caseous MAC is a rare echocardiographic finding. The echocardiographic prevalence of caseous MAC is reported to be 0.64% in patients with MAC2 and 0.068% in large series of patients of all ages.2 Caseous MAC appears as a round or spherical mass with echodense distinct outer borders with central areas of echolucency and without echocardiographic acoustic shadowing. The location and extension of caseous MAC should be accurately assessed and followed with echocardiography because it may lead to mitral stenosis3 or regurgitation4 when it extends to involve the mitral leaflets. The presence of MAC can reduce the angle of the mitral leaflet opening and cause valvular dysfunction.
Because caseous MAC is an unfamiliar condition, most cases are confused with other left atrial masses such as tumors, abscesses, or infective endocarditis. MAC should not be misinterpreted as an intracardiac tumor, abscess, or infective endocarditis (Table 1) because misdiagnosis may lead to unnecessary surgical resection.5 Myxoma is a common intracardiac tumor. When distinguishing between caseous MAC and a myxoma on echocardiography, it is important to note that myxoma is usually mobile, pedunculated, and attached to the myocardial wall along the interatrial septum. It usually lacks the calcified borders and interior echolucency seen in caseous MAC. Additionally, it is highly vascular compared with caseous MAC in which no blood flow should be visualized on color flow Doppler imaging. A myocardial abscess appears as a mass at the mitral–aortic intervalvular fibrosa with a homogenous echogenic appearance on echocardiography. It usually lacks large amounts of calcification and sometimes shows systolic flow within its cavity as visualized by color flow Doppler. Infective endocarditis appears on echocardiography as an oscillating mass on a support structure such as an abscess or a partial dehiscence of a prosthetic valve. Although other structures that may lie in the atrioventricular grooves include a dilated coronary sinus or left circumflex artery aneurysm, blood flow within those structures is invariably seen on color flow Doppler.
In this case, the location and features of caseous MAC were clearly visualized by intraoperative 3D TEE so that the entity could be identified. Although the previous use of 3D TEE for characterization of this lesion has been reported,6 the technology for 3D echocardiography has been advancing and is now capable of providing detailed delineation of the morphology of MAC. In summary, we demonstrated that 3D TEE was able to provide incremental value over 2D TEE and thus enable confident diagnosis and assessment of caseous MAC.
Clinician’s Key Teaching Points
By Nikolaos J. Skubas, MD, Massimiliano Meineri, MD, and Martin J. London, MD
- Calcification of the mitral annulus is a common clinical finding. It is characterized by immobile calcium deposits within the fibrous annulus that appear as typical hyperechoic structures with acoustic shadowing. When limited to the mitral annulus, they are not usually clinically relevant but if they extend into the valve leaflets may cause valvular dysfunction. Less common is the more friable, caseous variant.
- Caseous mitral annular calcifications appear as well-defined round or spherical masses attached to the mitral valve annulus and may develop along either side of the leaflets. They are avascular and move with the structures they are attached to, exerting a local mass effect. On echo imaging, they appear with a clear calcified outer border and central echolucent areas with no flow on color Doppler imaging.
- In this case, a well-defined, avascular spherical mass was noted on the ventricular side of the posterior mitral valve leaflet on baseline 2D TEE examination without valvular dysfunction. Its echocardiographic appearance was pathognomonic for caseous mitral annular calcification. Three-dimensional TEE identified 2 separate masses involving the base of the P2 and P3 scallops of the posterior mitral valve leaflet visible from both the ventricular and the atrial aspects. Three-dimensional multiplanar reconstruction allowed precise measurement of the 2 separate masses for later follow-up imaging.
- Caseous mitral annular calcifications not causing mitral valve dysfunction do not warrant surgical resection. However, they may be misinterpreted as other intracardiac masses that warrant surgical treatment such as myxomas, vegetations, or abscesses.
Name: Ryoji Iida, MD, PhD.
Contribution: This author helped conduct the study, analyze the data, and write the manuscript.
Attestation: Ryoji Iida approved the final manuscript.
Name: Tomonori Furuya, MD.
Contribution: This author helped write the manuscript.
Attestation: Tomonori Furuya approved the final manuscript.
Name: Takahiro Suzuki, MD, PhD.
Contribution: This author helped write the manuscript.
Attestation: Takahiro Suzuki approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
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