Imaging description

At cardiac MRI (CMR), mitral annular calcification (MAC) is low in signal intensity on bright blood, T1- and T2-weighted images and can appear as a smooth, multilobulated mass or masses in the region of the atrioventricular groove (Figure 3.1). Caseous, also known as liquefactive, MAC is a rare variant that is typically a larger, rounded mass with central liquefactive necrosis, composed of calcium, inflammatory cells, and cholesterol. Given that calcification is not well depicted by MRI, MAC can be mistaken for a cardiac tumor. Caseous MAC can occasionally be large – up to several centimeters in size and may displace mitral valve leaflets, resulting in valvular dysfunction such as regurgitation or stenosis. On post-contrast images, there is occasionally a thin rim of enhancement due to fibrous tissue surrounding the calcification (Figure 3.2). If CT is available, MAC is easy to identify on non-contrast images due to presence of high attenuation calcification (Figure 3.1).

Importance

MAC at CMR can be mistaken for a cardiac tumor or other type of cardiac mass, leading to inappropriate additional testing as well as patient anxiety. Although benign, the presence of MAC is a marker of increased cardiovascular risk. MAC was associated with a 50% greater likelihood of cardio vascular events at follow-up in the Framingham Heart Study and predicted both increased all-cause and cardiovascular death.

Typical clinical scenario

MAC is a common disorder. In the Multi-Ethnic Study of Atherosclerosis, MAC was detected by CT in 9% of a cohort of 6814 subjects from age 45–8. Caseous MAC is more rare, affecting < 1% of subjects with MAC. MAC is often discovered incidentally at echocardiography, and usually requires no further imaging. However, if the diagnosis is uncertain, patients may be referred to advanced imaging with MRI or CT.

Differential diagnosis

MAC should be differentiated from a true cardiac tumor. Location in the mitral annulus, low T1 and T2 signal intensity, and lack of enhancement are distinguishing characteristics.