Friday, August 22, 2008

Use of Bedside Ultrasound in Emergency Department for Detection of Abdominal Aortic Aneurysm (AAA)

Ultrasonography is a relatively easy to use, sensitive and specific bedside test in emergency department for the detection of AAA.

The main disadvantage is that a leaking or ruptured aneurysm can be difficult to distinguish from an enlarged but non ruptured aneurysm.

A leaking or ruptured AAA classically presents in patients
- who are older than 60 years
- have a history of hypertension
- and atherosclerosis
- and who develop severe abdominal, back, or flank pain following an episode of syncope

Less than 50% of patients present with the "classic" history of a tender pulsatile mass and hypotension.

Thus, a high index of suspicion must be maintained, especially in the older patient.

Renal colic, mechanical back pain, and diverticulitis are the most common misdiagnoses in patients with AAA.

The abdominal aorta is said to have an aneurysm when the distal aorta is dilated to a diameter of larger than 3 cm.

An AAA typically enlarges at a rate of 2-8 mm/year.

Because enlargement results in an increasing incidence of rupture (eg, a 7-cm AAA has a 19-32% rate of rupture per year) and because the mortality rate is much lower with elective repair than with emergent repair (3-5% vs 50%), general recommendations indicate that AAAs larger than 5-5.5 cm be electively repaired.

Two excellent resources on the use of Ultrasound in detection of AAA:
1. A Medscape article can be found here (click here).
This is a good article with flash videos downloads and step-by-step instructional guide

2. A very rich resource can be found on this website "Ultrasound Guide For Emergency Physicians". This can be reached by clicking here.
This is an excellent resource that have notes, images and video clips on common uses of Ultrasound in emergency department including FAST in trauma, hepatobiliary screening, etc.

Steps to begin with:

The probe is then rocked caudally, where a 3.5-cm abdominal aortic aneurysm is revealed.

1. Start in the transverse plane with the probe to “9 o’clock”, high in the epigastrium, using the liver as a sonic “window”.

Image above is taken from the Medscape article. Link to the access can be found by clicking here.

2. Identify the level of the proximal aorta, where the "seagull sign" (bifurcation of the celiac trunk) can be appreciated.

The shape of sea-gull seen due to the bifurcation of the celiac trunk.
Both images above are taken from the Ultrasound Guide for Emergency Physicians. Click here to go.

The ultrasound image of the bifurcation of the celiac trunk looks like the two wings of the sea-gull.

3. Identify the vertebral body (a dark, rounded shape, with dense shadow).

4. Identify the aorta on the patient’s left, and the IVC (patient’s right) “above” the vertebral body on the ultrasound image.

5. The abdominal aorta can be distinguished from the vena cava by its thicker wall, pulsations, noncompressible nature, and ability to detect pulsatile Doppler flow.


Dave said...

I don't think leaking / ruptured aneurysms being difficult to distinguish from enlarged ultrasounds is a major disadvantage.

Put simply, the main utility as you alluded to is detection. In a shocked patient, it is assumed to be leaking, so identification should result in a patient redlined to theatre. Non shocked patients should have an abdominal CT first as the situation allows, but common sense dictates that a stable patient with an identified AAA on US should have cross sectional imaging first.

Also, in the identification of the AAA, at least when I measure the diameter, it is preferable to measure in a longitudinal cross section to avoid over estimating cross sectional diameter if the angle of detection is < 90°

Anonymous said...

I really like your blog and i really appreciate the excellent quality content you are posting here for free for your online readers. thanks peace sandro

Brian Rike, DO said...

Ultrasound is definitely the fastest way to a diagnosis in a unstable patient with a leaking or ruptured AAA. Assuming the ultrasound is on and working - really depends on where you are practicing some facilities may actually have better CT capabilities without a ED US machine.


PLEASE NOTE: All contents in this blog are copyrighted materials, unless otherwise stated. Even if you encounter materials in this page without a copyright notice, it does not mean that it is not copyrighted (Click here to read TEN BIG myths on copyright explained). This is especially so as most nations are signatories of the Berne Convention on international copyright law (World Intellectual Property Organization). Nevertheless, I have licensed almost all the materials contained here under Creative Commons licenses strictly for educational, non-commercial purposes only. Kindly email me at should you want to use any of the materials for commercial purposes. Thank you.