Multimodality Imaging of the Anatomy of the Aortic Root

Abstract

The aortic root has long been considered an inert unidirectional conduit between the left ventricle and the ascending aorta. In the classical definition, the aortic valve leaflets (similar to what is perceived for the atrioventricular valves) have also been considered inactive structures, and their motion was thought to be entirely passive-just driven by the fluctuations of ventricular-aortic gradients. It was not until the advent of aortic valve-sparing surgery and of transcatheter aortic valve implantation that the interest on the anatomy of the aortic root again took momentum. These new procedures require a systematic and thorough analysis of the fine anatomical details of the components of the so-called aortic valve apparatus. Although holding and dissecting cadaveric heart specimens remains an excellent method to appreciate the complex "three-dimensional" nature of the aortic root, nowadays, echocardiography, computed tomography, and cardiac magnetic resonance provide excellent images of cardiac anatomy both in two- and three-dimensional format. Indeed, modern imaging techniques depict the aortic root as it is properly situated within the thorax in an attitudinally correct cardiac orientation, showing a sort of "dynamic anatomy", which admirably joins structure and function. Finally, they are extensively used before, during, and after percutaneous structural heart disease interventions. This review focuses on the anatomy of the aortic root as revealed by non-invasive imaging techniques.

Keywords: aortic root; cardiac magnetic resonance (CMR); computed tomography (CT); echocardiography.

Figure 1

(A) Computed tomographic image in multiplanar modality, showing the aortic root (AO) is the cardiac centerpiece, surrounded by the atria and the right ventricular outflow tract (RVOT). (B) The 3D volume rendering CT image in antero-posterior projection showing the obliquity of the aortic root (yellow arrow), sited posterior and rightward to the RVOT (red arrow). (C) Computed tomographic in multiplanar imaging modality showing the correct attitudinal orientation of the aorta. The black line, that joins the nadir of aortic sinuses, is near 30° tilted in respect to the horizontal red line, so that the left coronary sinus (LCS) and its leaflet are at the highest position among the right coronary (RCS) and non-coronary sinuses. (D) CT image in 3D volume rendering modality in antero-lateral projection showing the AO is surrounded laterally by the right atrial appendage (RAA). (E) CT image in 3D volume rendering modality in lateral projection, showing the space between the left atrium (LA) and the AO (yellow arrow) named “sinus transversum” filled up by epicardial adipose tissue. (F) The 2D transesophageal echocardiography in short-axis aortic view, showing the close proximity between the fossa ovalis (FO) and the non-coronary sinus (NCS) (see text).

Figure 2

(A) CT image of short-axis view of the aortic root from an aortic perspective. The gray-beige areas superimposed to the image indicate the myocardium enclosed at the bases of right coronary sinus (RCS) and left coronary sinus (LCS). (B) CT scan of volumetric image of the aortic root. The ventriculo–arterial junction is indicated by the yellow dotted line. The red areas below indicate the muscular myocardium enclosed in the bottom part of the sinuses. (C) Cardiac magnetic resonance showing the left ventricle (LV), the left atrium (LA), and the aorta (AO) in cross-section long-axis view. (D) Magnified image of the structures in the red square of the panel C. The double-headed arrow marks the extension of muscular sleeve on the right coronary sinus (RCS). (E) Computed tomography showing the LV, the LA, and the AO in cross section long-axis view. (F) Magnified image of the structures in the red square of the panel C. The double-headed arrow marks the extension of muscular sleeve on the RCS.

Figure 3

(A) The 2D TEE in long axis-view showing a peri-annular aortic abscess (arrow). (B) Same case of panel A showing the abscess may extend posteriorly on the crux cordis (arrow). (C) The 3D TEE in long-axis view. The red curve lines mark the position of His bundle immediately under the MS (asterisk) and its bifurcation. (D) CT multiplanar reconstruction showing the course of the His bundle and its branches (red lines). The light blue cylinders are representative of the position of the implanted valve. AO = aorta; LV = left ventricle; LA = left atrium; RA = right atrium; RV = right ventricle.

Figure 4

Anatomic specimen components of the aortic root: the sinus–tubular junction (white thick dotted line), the crown-shaped annulus (red dotted line), and the ventricular–arterial junction (black dotted line). The virtual basal ring (white thin dotted line). MS = membranous septum; ILT = interleaflet triangle.

Figure 5

(A) The 2D and (B) 3D TEE long-axis view showing the echocardiographic annulus. (C,D) Multiplanar reconstruction using the 3D data set showing the virtual annulus. (E,F,H) CT scans showing the 3 nadirs (marked by the red, green, and yellow circles). (G) Dedicated software aligns the three nadirs in the same plane making possible measurements of diameters (white dotted lines) and circumference (blue line).

Figure 6

(A) CT in volume rendering format and (B) 3D TEE showing the typical crown-shaped configuration of the anatomical annulus (dotted line).

Figure 7

The three inter-leaflets triangles visualized with CT volume rendering format (dotted line). NCS = non-coronary sinus; LCS = left coronary sinus; RCS = right coronary sinus.

Figure 8

(A–D) Tridimensional 3D TEE showing the progressive closure of aortic leaflets during the systole.

Figure 9

(A) The 3D TEE magnified image showing the bird’s nest appearance with the lunula, body, and hinge line. (B) Anatomic specimens showing the Lambl’s excrescences (arrow).

Figure 10

(A) CT Volume rendering modality showing the origin of right coronary artery arise at the level of sinutubular junction (black dotted line). (B) The 3D TEE longitudinal cross-section showing the orifice of coronary artery (arrow) at level of sinutubular junction (white dotted line). (C,D) CT multiplanar image modality showing the measurements of the distance (double-headed arrow) between the coronary ostia (white dotted line) and the virtual annulus (yellow dotted line). (E) The 2D TEE multiplanar reconstruction derived by 3D data set in short-axis view of the aorta showing the orifice of LAD (curved arrow). The white dotted line indicates the longitudinal cross-section plane that shows the image of the panel. (F) From this image, the distance between the coronary ostia (white dotted line) and the virtual annulus (yellow dotted line) can be measured (double-headed arrows).