The Big Mitral Annulus Calcification (MAC)　― Tissue Characterization and Assessment of Haemodynamic Impact Using Cardiac Magnetic Resonance ―

A 79-year-old asymptomatic male with a history of dyslipidaemia and hypertension was referred for a cardiac magnetic resonance (CMR) scan to characterize a left atrial (LA) mass. CMR demonstrated a large mass in the posterior mitral annulus (53×32×28 mm) extending into the base of the posterior mitral valve (MV) leaflet (causing mild leaflet restriction) and the posterior LA wall, and into the basal/mid-left ventricular walls. The mass was significantly hypointense on steady state in free procession, T1-weighted and T2-weighted turbo spin echo images, and T2-short tau inversion recovery (Figure A–D). On T1/T2 mapping, both the native T1~300 ms (Figure E) and T2~30 ms (Figure F) values of the mass were low (at 1.5T). On first-pass perfusion and early gadolinium-enhanced images the mass was extremely hypoperfused (Figure G,H). On late gadolinium-enhanced images there was a rim of enhancement (i.e., fibrous tissue) encapsulating the mitral annulus calcification (MAC) (Figure I). These features are typical for densely calcified masses such as MAC due to the lack of free mobile protons, the zero spin and no intrinsic MR signal of Ca²⁺.

Figure.

Cardiac magnetic resonance images of a 79-year-old asymptomatic male with a history of dyslipidaemia and hypertension referred for a left atrial mass. The mass was hypointense on (A) steady state in free procession, (B) T1-weighted and (C) T2-weighted turbo spin echo images and (D) T2-short tau inversion recovery. On T1/T2 mapping, both the native T1~300 ms (E) and T2~30 ms (F) values of the mass were low (1.5 T). On first-pass perfusion (G) and early gadolinium-enhanced images (H) the mass was extremely hypoperfused. On late gadolinium-enhanced images there was a rim of enhancement (fibrous tissue) encapsulating the mass (I). These features are typical of mitral annulus calcification.

Calcification of the MV may be related to degenerative changes, atherosclerosis, radiation therapy, increased MV stress, calcium-phosphorus metabolism, or metabolic disorders.¹ Caseous MAC is a rare form of mitral calcification (<1% of MAC cases) and usually a benign condition.² Sometimes, caseous MAC may be mistaken for cardiac calcified amorphous tumor, which is a rare intracavitary cardiac mass, with the microscopic feature of calcification carrying a risk of embolic events.³ However, caseous MAC is located at the mitral annulus level with well-defined boundaries, and should not be misinterpreted as a cardiac tumor, a thrombus, or an abscess, leading to unnecessary interventions.

References

• 1.   Abramowitz Y, Jilaihawi H, Chakravarty T, Mack MJ, Makkar RR. Mitral annulus calcification. J Am Coll Cardiol 2015; 66: 1934–1941.
• 2.   Arora H, Madan P, Simpson L, Stainback RF. Caseous calcification of the mitral annulus. Tex Heart Inst J 2008; 35: 211–213.
• 3.   de Hemptinne Q, de Canniere D, Vandenbossche JL, Unger P. Cardiac calcified amorphous tumor: A systematic review of the literature. Int J Cardiol Heart Vasc 2015; 7: 1–5.