The central veins demonstrate greater symmetry than the supra-aortic arteries (Fig. 8.2). The internal jugular veins of the neck and subclavian veins from the upper extremities are confluent, forming the right and left brachiocephalic veins. The external jugular veins also drain into the subclavian veins bilaterally, near the originations of the brachiocephalic veins. The right and left brachiocephalic veins converge to form the superior vena cava (SVC) at about the level of the aortic arch. The SVC lies to the right of the arch, causing a bit of asymmetry. The right brachiocephalic vein descends directly into the SVC as a short venous segment, but the left brachiocephalic vein is longer and sharply angulated because of the position of the SVC. The left brachiocephalic vein courses obliquely from the left internal jugular (IJ) vein to the right chest, lying anterior to the branch arteries of the arch. Both brachiocephalic veins converge to form the superior vena cava. Approximately 7 cm in length, the SVC is in contact with the pleura of the right lung, the trachea, and aorta. There are no valves in the brachiocephalic trunks or SVC.

The arch and branches are a neglected area that is seldom imaged with ultrasound because of dense ultrasound reflections produced by bone and lung air. It is, however, described as part of a standard echocardiographic assessment made through a suprasternal approach [8].

The suprasternal notch is the midline depression that lies at the base of the neck, between the sternum and larynx. Echocardiography uses the notch to visualize the ascending aorta, arch, and descending thoracic aorta as a means for evaluating the aorta for valvular insufficiency, dissection, aneurysm, or coarctation [9]. Though it is described as a standard echo approach, the image is often less than satisfactory and is seldom used in adult echo.

The echocardiographer uses a 2–5 MHz transducer to visualize the ascending aorta, arch, and descending aorta. The transducer produces a small footprint for the more superficial arch branches and is less suited for branch vessel assessment. For the neck, vascular sonographers use high-frequency (5–10 MHz) linear probes to image the extracranial cerebrovascular branches at the carotid bifurcation. The examination approaches the cervical carotid arteries from the lateral neck, alongside the sternocleidomastoid muscle. The scan typically ends centrally at the right common carotid origin and left common carotid artery at the neck base.

As a compromise, the midline, suprasternal approach should be our approach to the supra-aortic vessels, using a low-frequency curvilinear probe rather than the small footprint echo or the high-frequency linear probe. The obvious drawbacks to imaging the arch and its branches from this angle include the following: (1) Interference from the sternum and claviculae which severely limits access. The ultrasound beam is projected downward through a narrow acoustic window which limits the anterior-posterior projection by the sternum and neck. (2) The truncal arteries project directly toward the probe, and veins project directly away from the probe. The resulting B-mode echoes are weakly reflective and poorly illuminate the walls of the central branches. (3) Color Doppler compensates for the weak B-mode image, but the number of large vessel flows and color artifacts picked up from the bright echoreflective surfaces of the mediastinum and pleura produce a confusing image with large swaths of color.

To overcome these problems, recognizing the anatomy of the arch and brachiocephalic veins is important to scanning the central vessels. It is also important to maintain an orientation that is based upon the known ultrasonic anatomy. The examination can be performed by first placing the curvilinear transducer above the sternum and positioning the probe to produce a panoramic view of both common carotid arteries and internal jugular veins at the base of the neck (Fig. 8.3). With this view as the reference point, the scan can be extended centrally by gray scale and color. The right common carotid artery will be seen to rapidly converge with the subclavian artery to become the innominate artery. On the left, the common carotid artery will be seen to simultaneously continue uninterrupted toward the arch. As the probe is projected centrally, both the innominate and left common carotid arteries will approach one another. The larger innominate artery will approach midline from the patient’s right, and the left common carotid artery will course obliquely from the left. From further left, the left subclavian artery will course toward the arch from the clavicle.

The arteries and veins of interest lie in front of the trachea. Because the arch projects obliquely from right to left and anterior to posterior, the probe positioned for a transverse view of the innominate and left common carotid arteries will also capture the aorta in near transverse. The aorta will be seen in gray scale as a 2−3-cm pulsatile mass. By color, flow in the aorta will be notably disturbed. Flow in the innominate and left common carotid will be much more uniform and easily traced as tracks of color flow directed toward the probe. Both arteries can be interrogated by spectral Doppler as they approach the aorta.

Once the relative positions of the arteries are identified, the innominate artery (Fig. 8.4) and left common carotid artery (Fig. 8.5) may be imaged individually in the longitudinal view by rotating the ultrasound probe on the neck base to the left of midline.

The left subclavian artery may be the most difficult to follow. To visualize the subclavian, the transducer probe will be positioned above the clavicle, projecting the heel of the probe toward the left posterior aspect of the notch (Fig. 8.6). Ultrasound reflections will capture bright reflections from the pleura and left lung. Artifactual duplication of the left subclavian artery by B-mode and color could then result from mirror imaging reverberation (Fig. 8.6).

The subclavian artery should be identified as the color flow pattern that lies superficial to any color artifact. To avoid further confusion, the left subclavian artery could be followed from the axillary artery, below the clavicle, through the thoracic outlet to the subclavian artery.

Difficulties in imaging may be associated with con­figuration of the arch. The arch has been described in coiled and uncoiled configurations with the supra-aortic trunks originating from different points of the arch [10]. The better configuration positions the innominate on the right edge of the apex, and the left subclavian on the left edge. The take-off points, located on the superior wall of the arch, are ­optimally positioned for ultrasound imaging and endovascular cannulation. The more difficult imaging configuration occurs when the innominate artery arises from the aorta, before the apex, and its origin lies below the level of the apex. In this “uncoiled” position, the left common carotid and subclavian arteries may be similarly displaced to the right. The deeper take-off of the innominate may prevent adequate ultrasonic visualization as well as increase the difficulty of endovascular cannulation.