Mitral Annular Calcification Workup

Updated: Mar 06, 2017
  • Author: Saurabh Sharma, MD; Chief Editor: David J Maron, MD, FACC, FAHA  more...
  • Print
Workup

Approach Considerations

Imaging studies

Mitral annular calcification (MAC) is usually an incidental finding on cardiac imaging. With transthoracic echocardiography, on the parasternal or apical views, MAC is identified as an echodense band or mass in the atrioventricular groove. MAC is seen all the way through systole and diastole, distinguishable from the posterior mitral valve leaflet. [86] Although most commonly affecting the posterior annulus, it can occasionally involve the anterior annulus, or interannular fibrosa, as noted in the video below.

Transesophageal two-dimensional echocardiography. Mitral annular calcification is especially prominent in the anterior annulus (interannular fibrosa). A mobile element extends from the calcified anterior annulus into the aortic outflow tract.

Calcification can extend from the annulus onto the leaflets, limiting their mobility. It is not unusual to find the posterior leaflet encased in calcium and completely immobilized. This usually has no physiologic consequences. However, calcification extending onto the anterior leaflet and limiting its mobility may be associated with transmitral gradients. [68] Caseous calcification is less echodense than typical MAC; a central echolucent zone is usually present and acoustic shadowing is generally absent.

Cardiac magnetic resonance imaging (MRI) and computed tomography (CT) scanning have also been used in the evaluation of MAC [87] and can be particularly helpful in differentiating caseous MAC, cardiac tumor, and thrombus when poor quality images are seen on echocardiography. [88, 89]

Next:

Histologic Findings

Biopsy is never needed for the diagnosis of mitral annular calcification (MAC). In its most characteristic configuration, it forms a semilunar deposit of calcium within the annulus fibrosus, with limited extension to the leaflet tissue. This is different from the calcification seen in rheumatic valvular disease, which usually involves the commissures and the leaflet tissue with only late extension to the annulus.

Carpentier et al studied pathologic specimens of 68 patients (mean age, 62 y) with extensive MAC and significant mitral regurgitation. They found calcification of at least one third of the posterior annulus in 88% of cases, with calcification of the entire posterior annulus in 10%. [66] Calcium formation was generally encapsulated in a fibrous sheath. However, fibrous encapsulation was not found in areas of myocardium infiltrated by the calcific process. Beyond the limits of the calcification, the remaining annulus fibrosus usually displayed fissures and zones of dehiscence. These defects were filled with lipoid substances, platelets, and red blood cell aggregates. In caseous MAC in particular, the histopathologic findings are characterized by central liquefaction necrosis and scattered calcifications that are predominantly located in the peripheral regions. [27]

Previous
Next:

Staging

In general, no standard grading system by echocardiography is recognized. Many studies have classified the severity of mitral annular calcification (MAC) by measuring its thickness on M-mode echocardiography at the point of greatest width. Thickness greater than 1 mm but less than 4 mm has been considered mild to moderate, whereas thickness greater than 4 mm has been considered severe. MAC greater than 4 mm has been found to be an independent predictor of myocardial infarction and valvular disease. [33]

Other investigators have graded the severity of MAC by dividing the posterior annulus in thirds and adding up the number of thirds involved. Still others have looked at annular calcification in the context of overall cardiac calcification, using semiquantitative systems to grade calcification in the aortic and mitral valves, aortic root, and submitral apparatus, as well as the mitral annulus. [25, 83]

Previous