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Caution with the Aorta

11/27/11 - As an additional Image of the Week, please see Images #1 & #2.

Image 1

AA1

Image 2

 AAA2

The scenario associated with these images is a patient with abdominal pain. The US image shows the cross-section of the aorta and an incorrect measurement of the diameter.

To correctly image the aorta, 5 images should be obtained:

  1.  Proximal Aorta – cross section
  2. Mid Aorta – cross section
  3. Distal Aorta – cross section showing bifrication
  4. Iliacs – cross section showing individual diameters
  5. Longitudinal view – capturing celiac trunk and SMA. 

The aorta is imaged in cross-section with the curvilinear probe, indicator to the right, and the diameter is measured from outer wall to outer wall. The lone longitudinal image rotates the probe 90 degrees with the indicator to the head of the patient.

In the US image 1, the aorta measured right at 3.0 cm – the upper limit of normal. Take a closer look at the image – what is missed? How could the measurement be improved?

The ED sonographer did not include the area of intra-luminal thrombus. Had this been measured appropriately, the diameter would be much larger and should trigger an immediate CT to rule out aneurism, or if unstable STAT vascular surgery consultation. Also note the excessive depth – decreasing the depth in this situation may have led to better visualization of the thrombus and more appropriate measurement.

The patient did ultimately get a CT of the Abdomen showing a saccular aneurism and the patient was appropriately managed.  

AAA evaluation with US is a critical skill and part of the ACEP Emergency Ultrasound Guidelines published in 2008 (see attached). Skill with this evaluation permits early mobilization of resources and may have striking benefit in patient care. Please be careful about how you measure and maximize you ability to see with using the depth feature to your advantage.

Thank you for your continued use of bedside US.