- Sweep down past the umbilicus until the single aorta becomes two, narrower vessels. This is where the aorta bifurcates into the right and left iliac arteries. Occasionally you may encounter an aneurysm in the iliac artery.
- As you scan inferior to the the renal arteries you will approach the distal abdominal aorta.
Visualize and measure the distal aorta.
- The distal abdominal aorta is imaged as the probe approaches the umbilicus.
- This is when the aorta is most superficial, and you may need to decrease your depth.
- Measure the distal aortic diameter once you have obtained a clear view.
- To see the Mid Aorta, slide your probe inferiorly, distally from the SMA, keeping the aorta in view at all times.
Visualize and measure the Mid Abdominal Aorta
- The mid abdominal aorta lacks distinct anatomical landmarks. Occasionally, you will be able to visualize the renal arteries as an inferior boundary for this portion of the exam.
- Measure the mid-aortic diameter once you have obtained a clear view.
For the short axis abdominal aorta ultrasound protocol, you will examine the short axis of the abdominal aorta from the celiac trunk down to the iliac bifurcation in 3 main sections: proximal, mid, and distal. You will also measure the aortic diameter in each section.
Step 1: Proximal Abdominal Aorta
In the proximal abdominal aorta, you will distinguish the aorta from the IVC, view the celiac trunk/superior mesenteric artery, and measure the aortic diameter.
Place your probe just below the xiphoid process, slightly left of midline to the patient , with the probe indicator facing the patient’s right/examiner’s left (“9 o’clock”) to obtain a short axis/transverse view of the proximal aorta.
Adjust the depth until the hyperechoic vertebral body and its dense shadow are visible at the bottom of the screen.
- Identify the Aorta, a thick-walled, hypoechoic, pulsatile circle just above the vertebral body, slightly right of midline (patient’s left) on the screen.
- Identify the IVC. It won’t be as circular as the aorta, will lie left of midline on the screen (patient’s right), and is usually collapsible with respirations.
- Keep the probe perpendicular to the abdominal wall for the best short axis view, and accurate subsequent measurements.
- Tip: If you cannot see these structures, gas in the transverse colon may be blocking your view. Apply constant downward pressure and rock your probe back and forth to displace bowel gas and get your window. If that doesn’t work, try placing your patient in the left lateral decubitus position or attempt the lateral views of the aorta.
Visualize the Celiac Trunk by sliding your probe slightly inferiorly.
- The celiac trunk branches into the common hepatic artery and splenic artery in the “seagull sign” just anterior to the celiac trunk coming off the abdominal aorta.
Visualize the superior mesenteric artery (SMA). Slide your probe inferiorly a bit further – it shouldn’t be far, since the SMA originates just distal to the celiac trunk. It will appear as a smaller, circular, hypoechoic structure just anterior to the abdominal aorta.
- In this plane, you may also see the left renal vein between the SMA and the aorta, as well as the splenic vein anterior to the SMA.
- These are the structures implicated in nutcracker syndrome when the left renal vein gets trapped between the aorta and SMA.
Measure the aorta in its widest diameter.
- Freeze the image.
- Take measurements from outer wall to outer wall at it’s widest diameter.
- Obtain both an anteroposterior measurement and a transverse measurement if possible.