The normal aortic valve is a trileaflet valve with the left and right cusps giving rise to the left and right coronary arteries, respectively (Fig. 8.6). The noncoronary cusp is in fibrous continuity with the anterior leaflet of the mitral valve. The aortic valve has a semilunar attachment to the junction of the left ventricular outlet and the aortic root. The cusps have a main core of fibrous tissue with endocardial linings on each surface. The cusps are thickened at the midpoint to form a nodule. The area of the aortic orifice in a normal adult is 3.0–4.0 cm². The imaging plane of the aortic valve to identify the cusps is defined by obtaining long-axis views of the LVOT and the proximal aorta (3-chamber and 2-chamber views). The valvular plane is then obtained by orthogonal views perpendicular to the annulus (Fig. 8.7).

CT and MRI allow a detailed understanding of the complex three-dimensional aortic root anatomy, including the crown-shaped anatomic aortic annulus, the virtual basal ring, the sinuses of Valsalva, the valve leaflets, and the sinotubular junction (Figs. 8.8 and 8.9). The ascending aorta consists of the aortic root and the tubular segment [6]. The border between the two is called the sinotubular junction. The aortic root, representing the outflow tract from the left ventricle, provides the supporting structures for the leaflets of the aortic valve and forms the bridge between the left ventricle and the ascending aorta. The top end of LVOT, the aortic annulus, the commissures, the sinuses of Valsalva, the coronary ostia, and the sinotubular junction are the framework in which the valve leaflets are hanging. The annulus is an oval-shaped, 3-pronged coronet with 3 anchor points at the nadir of each aortic cusp [7]. The attachment of the aortic cusps is semilunar, extending throughout the aortic root from the LV distally to the sinotubular junction. The anatomic boundary between the left ventricle and the aorta, however, is found at the point where the ventricular structures change to the fibroelastic wall of the arterial trunk. This locus is not coincident with the basal attachment of the leaflets of the aortic valve.

The root is much wider at the midpoint of the sinuses than at either the sinotubular junction or the basal attachment of the leaflets [8]. This becomes of significance when considering measurements of the annulus because the hinges of the leaflets extend through all these three levels. The appropriate measuring points are at the bottom of the basal valvular attachments, at the widest point of the sinuses, and at the sinotubular junction. Beyond diameter measurements, the perimeter appears especially useful for definition of the exact size in multiplanar CT or MRI. An exact visualization of the aortic root and ascending aorta is important as diseases of these structures are commonly related to bicuspid aortic valve disease and in an interventional and surgical context.

Cardiac volumes and ejection fraction have important prognostic and therapeutic implications in cardiology. Systolic left ventricular ejection fraction is a strong predictor for prognosis in valvular heart disease [9]. Left ventricular end-diastolic volume and end-systolic volume measurement by section summation of contiguous MRI short-axis images is the reference standard for left ventricular function. Cine images in short-axis and two long-axis orientations are used for left ventricular function analysis by guide-point modeling ventricular function analysis (Fig. 8.10).

LVOTO results in concentric hypertrophy which is characterized by a reduced end-diastolic radius-to-wall thickness ratio or volume-to-mass ratio (Fig. 8.11). The left ventricular response to LVOTO is complex. It consists of a combination of wall thickening and a change in cavity size with associated effects on systolic and diastolic function. Concentric hypertrophy is defined by a combination of left ventricular hypertrophy and increased relative wall thickness. Patients with LVOTO had wide variation in left ventricular geometry and function [10]. Left ventricular hypertrophy is associated with myofibrillar hypertrophy, but also fibrosis, which is the deposition of collagen and fibronectin. Focal scarring can be observed in severe left ventricular hypertrophy caused by aortic stenosis and correlates with the severity of left ventricular remodeling [11] (Fig. 8.11). The amount of myocardial fibrosis by delayed contrast enhancement is associated with the degree of left ventricular functional improvement and all-cause mortality late after aortic valve replacement in patients with severe aortic valve disease [12].

The normal aortic valve is trileaflet. Congenital forms of valve disease are either unicuspid, bicuspid, or quadricuspid. Bicuspid aortic valve is the most common congenital cardiac anomaly occurring in 1–2 % of the population with a male predominance (4:1) [13] (Fig. 8.12). Mutations in the NOTCH-I gene have been related to bicuspid aortic valve. Valve dysfunction in BAV is characterized by an earlier onset and a higher rate of progression in comparison to patients with tricuspid aortic valve disease [14]. Further, BAV has a predisposition to infective endocarditis [15]. Aortic stenosis is the most common complication of patients with BAV [16]. Twenty percent of patients with bicuspid aortic valve have an associated cardiovascular abnormality, such as patent ductus arteriosus or aortic coarctation. Aortic stenosis does not become hemodynamically significant unless the valve area is reduced to approximately 1.0 cm².

Bicuspid aortic valve stands for a common congenital aortic valve malformation with heterogeneous morphologic phenotypes (Fig. 8.13). In general, a purely bicuspid aortic valve has only two cusps and has a characteristic fish-mouth appearance on short-axis images. Histopathological findings, however, show additional phenotypes of the bicuspid aortic valve regarding to the number of raphes, spatial position of cusps or raphes, and the functional status of the valve [16]. Thus, over the past years, different bicuspid aortic valve classifications were described. These classifications, however, are not uniform and easily applicable. Recently, a systematic classification of BAV with respect to the numbers and spatial position of the cusps and raphes, as well as the functional status, was found reliable and appropriate for a classification system from a surgical point of view (Table 8.1) (Fig. 8.14) [17]. By applying Sievers’ classification system, MRI and CT allow excellent characterization of valve phenotype in patients with bicuspid aortic valve for improved management of this entity (Figs. 8.15, 8.16, and 8.17) [18–21].