## 3 Computed Tomography and Mitral Valve  
### Anatomy of the Mitral Valve  
The mitral valve (MV) apparatus is composed of different parts: valvular annulus, two leaflets, chordae tendineae, and papillary muscles (Figure 9a,b).  
The MV annulus has a saddle shape. Its anterior flat portion, thus, the superior \"horn\", is connected by collagen fibers with the aortic annulus at the level of the noncoronary and the left aortic valve cusps. This fibrous part is called the actorunitral junction [60]. The posterior part of the mitral annulus includes the low saddle points in proximity to the lateral and medial commissures and the posterior saddle horn. This posterior part of the annulus is in continuity with the flexible, less fibrotic endocardium and may be subject to dilation. For this reason, it follows the myocardial contraction and relaxation, accentuating saddle height and decreasing circumferential area [61]. Notably, the MV annulus is surrounded by critical vascular structures, particularly by the coronary sinus (CS) posteriorly and the left circumflex artery laterally.  
The anterolateral and posteromedial commissures separate the anterior and the posterior MV leaflets. The two MV leaflets are significantly different in size. The anterior leaflet, during systole, configures the posterior part of the left ventricular outflow tract, occupies one-third of the annulus, and is longer than the posterior leaflet, which sticks to two-thirds of the annulus. The posterior leaflet typically has two indentations which divide it into three individual scallops: a P1 lateral scallop (adjacent to the left atrial appendage), a larger central P2, and a medial P3 scallop according to [PERSON]'s classification. Contrarywise, the anterior leaflet is not anatomically divided into scallops, but its segments are referred to as A1, A2, and A3, corresponding to P1-3 [60].  
The subvalvular apparatus of the MV includes chordae tendineae and papillary muscles. The primary cords anchor to the free edges of the leaflets, the secondary ones to the ventricular surface of the leaflets, and the tertiary ones originate from the left ventricular wall or muscle trabeculae at the posterior leaflet of the VM. Their function is to maintain, during systole, both leaflets in a position that allows their coaptation in systole without protrusion into the left atrium [62; 63]. As far as the papillary muscles are concerned, the  
Figure 9: (**a**) Transverse and (**b**) sagittal planes of the mitral valve.  
interolateral muscle arises from the apical-lateral third of the left ventricle. In contrast, the posteromedial muscle derives from the middle of the lower wall of the left ventricle. From their apex, the papillary cords take origin [64]. Their vascularization is important to understand some complications of infarction: notably, the left anterior descending and diagonal or marginal coronary branches feed the anterolateral papillary muscle; instead, in most cases, only one coronary artery (depending on the dominance, circumflex or right coronary artery) feeds the posteromedial papillary muscle. The different vascularization allows us to understand the susceptibility of the latter to ischemia and rupture.