US Probe: Ultrasound for Abdominal Aortic Aneurysm

Written by Wendy Lin, MD (Emergency Physician; Icahn School of Medicine at Mount Sinai) // Edited by: Stephen Alerhand, MD (@SAlerhand – Emergency Physician and Ultrasound Fellow, Icahn School of Medicine at Mount Sinai) and Manpreet Singh, MD (@MPrizzleER – Assistant Professor in Emergency Medicine / Department of Emergency Medicine – Harbor-UCLA Medical Center)


Case

A 71 year-old male with a past medical history of hypertension, hyperlipidemia, and 25 pack-year smoking history presents to the ED with a week of vague abdominal pain that has been getting worse. ROS is positive for 3 days of dizziness on getting up from his couch.

Vital signs are within normal limits. On exam, the patient is AAOx3, mildly uncomfortable on the stretcher. Abdominal exam is notable for a pulsatile mass in the mid abdomen.

You are suspicious for a ruptured abdominal aortic aneurysm (AAA) and grab the ultrasound machine right away.


What is the utility of bedside ultrasound for AAA in the ED?

• First published in 1989 [1]

• 2013 systematic review in Academic EM [2]
> Bedside US for AAA done by EM physicians
> Sensitivity 97.5-100%, specificity 94.1-100%

• 2014 retrospective study in European Journal of EM [3]
> Bedside US improved time to diagnosis (51 min from 111 min)
> This was not statistically significant but the study was small (~60 patients per group)

Considerations and indications [4]

• Reasonable indications include all patients >50 years old with unexplained hypotension, dizziness, syncope, cardiac arrest

• “Classic” presentation = Pain (abdominal, back, flank), palpable abdominal mass, hypotension
> But be careful — this triad is only found in < 25% of cases!

• Pain is the most consistent sign – found in 80% of patients presenting with AAA
> 80% abdominal pain
> 60% back or flank pain
> 22% groin pain

• Often presents with referred pain to scrotum, buttocks, thighs, shoulders, and/or chest

• Many are misdiagnosed with renal colic, diverticulitis, MSK pain


This patient’s bedside ultrasound…

Transverse view of the aorta in the mid abdomen. Measurement of the diameter from outer wall to outer wall is 3.73 cm, consistent with AAA.

Longitudinal view of the aorta. This view is not the best for measuring an accurate aorta diameter, but it can often draw your attention to a saccular aneurysm that would have been easily missed on a transverse view.

Transverse clip of aortic bifurcation into iliac arteries


Key points to remember while you are scanning

1. An aorta larger than 3 cm in diameter is considered aneurysmal. A common iliac artery larger than 1.5 cm in diameter is also considered aneurysmal.
2. 90% of AAA’s occur distal to the renal arteries. Be sure to scan all the way down until you see the bifurcation of the aorta into the left and right common iliac arteries. This usually happens near the level of the umbilicus. If the umbilicus is in your way, place your probe at the upper edge of it and fan distally.
3. Always measure aorta diameter from outer wall to outer wall. Measuring the inner wall can mislead you to measure only a false lumen due to an intramural thrombus. Plus, it is better to overestimate than underestimate in such a deadly diagnosis.
4. Two most common obstacles are bowel gas and obesity.
a. You may obtain better images with the patient in the lateral decubitus position.
b. Move slightly off midline and fan towards the aorta (only in the transverse view!).
c. Apply continuous pressure for 1-2 minutes or jiggle the probe to encourage peristalsis.

References/Further Reading:

[1] Jehle D, Davis E, Evans T, et al.: Emergency department sonography by emergency physicians. Am J Emerg Med 7:605–611, 1989.
[2] Rubano, Elizabeth, Ninfa Mehta, William Caputo, Lorenzo Paladino, and Richard Sinert. “Systematic Review: Emergency Department Bedside Ultrasonography for Diagnosing Suspected Abdominal Aortic Aneurysm.” Acad Emerg Med Academic Emergency Medicine 20.2 (2013): 128-38.
[3] Reed, Matthew J., and Lai-Ting Cheung. “Emergency Department Led Emergency Ultrasound May Improve the Time to Diagnosis in Patients Presenting with a Ruptured Abdominal Aortic Aneurysm.” European Journal of Emergency Medicine 21.4 (2014): 272-75.
[4] Ma, O. John, James Mateer R., Robert Reardon F., and Scott Joing. “Abdominal Aortic Aneurysm.” Ma and Mateer’s Emergency Ultrasound. 3rd ed. N.p.: n.p., n.d. 225-45.

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