The aorta cannot be compressed with the transducer.
The diameter of the aorta gently tapers from 2.5 cm superiorly to 2.0 cm inferiorly.
The lumen of the vena cava becomes smaller during inspiration.
Locate and identify the aorta and vena cava.
Demonstrate the aorta and vena cava in their entirety.
Locate and identify the branches of the aorta and the vena cava.
Demonstrating arterial and venous pulsations
Demonstrate the aorta in an upper abdominal longitudinal scan. Notice the firm beat of its pulsations. Now image the vena cava in longitudinal section and observe the soft, double-beat pattern of its pulsations.
Evaluating the vessel walls and lumina
Image the aorta in longitudinal section. Look at its thick, echogenic wall. Occasionally a typical three-layered wall structure can be seen (Fig. 3.7). Note how the size of its lumen does not change during pulsations or during inspiration/expiration. Apply pressure over the aorta with the transducer and notice that it is not compressible. The normal aorta tapers from above downward, its diameter decreasing from approximately 2.5 cm to 2.0 cm.
Define the vena cava in longitudinal section. Notice its thin wall and the changes in its caliber during the pulse phases. Have the subject breathe in and out (Figs. 3.8, 3.9) and observe how the lumen narrows during inspiration.
Abnormalities of the aortic wall and lumen
Aortic aneurysm. Most aortic aneurysms occur at an infrarenal level, and generally they are easy to detect. A saccular aneurysm (Fig. 3.14) appears as a circumscribed, asymmetrical outpouching of the aorta, while a fusiform aneurysm (Fig. 3.15) uniformly affects the circumference of the vessel (Fig. 3.16). With a dissecting aneurysm, the intimal flap can be recognized as a bright echo (Fig. 3.17). Table 3.1 reviews the sonographic features of aortic aneurysm.
Distension > 30mm
Signs of aortic sclerosis
Possible partial thrombosis
Aortic aneurysms tend to enlarge over time. The larger the aneurysm, the more rapid its progression. Aneurysms less than 5 cm in diameter grow by 2–4mm each year. Cases of this kind should be scanned every three months to evaluate size. Aneurysms with a diameter of 5 cm or more grow by up to 6mm per year. These cases should be evaluated for surgical treatment. With aneurysms larger than 7 cm, the risk of rupture in one year is greater than 50%.