Aortic ultrasound

Background

Aortic ultrasound should be utilized to assess for aneurysm or dissection
Aneurysm is defined as 3cm (150% the upper limit of normal) at the level of the renal arteries (L1-2 vertebral body level)
Risk of AAA rupture significantly increases at 5cm but should be ruled out in the proper clinical setting when >3cm
AAA’s are most commonly infrarenal
EM providers have an accuracy of 100% in assessing for AAA^[1]
An intimal flap is 67–80% sensitive and 99–100% specific for dissection^[2]

Indications

Classic triad for AAA is pain, hypotension, and pulsatile mass

Technique

5-Point Assessment

Select probe
- Curvilinear/large convex probe (phased array probe may substitute)
Location
- Start at the superior aspect of the abdomen below the xyphoid process
- Visualize aorta on the patient’s left, IVC on the right, and vertebral shadow posteriorly
Transverse views
1. Proximal aorta
2. Mid-aorta
3. Distal aorta
4. Aortic bifurcation
Longitudinal view
1. Distal aorta (to assess for saccular aneurysms)

Findings

AAA identified when diameter measured from outer wall to outer wall (including mural thrombus if present) is >3cm
Iliac vessels at bifurcation, outer wall to outer wall <1.5 cm^[3]
Abdominal aortic dissection can be identified as an intimal flap

Images

Normal

Abnormal

Pearls and Pitfalls

Measurements should be done in a transverse view of the aorta for best wall to wall measurement
- Avoid oblique measurements which can be falsely large
IVC can be differentiated by aorta as it is on the patient’s right, thin-walled, nonpulsatile, and compressible (depending on habitus)
Constant gentle pressure and jiggling the probe can help to move bowel gas to visualize the aorta
In the setting of ruptured AAA, blood may not show up in a fast exam if the bleeding is retroperitoneal
AAA vs Dissection
- Dissections will continue while AAA typically are located in single area
- Dissections can be a normal diameter
Mural thrombus can cause falsely small measurements
Utrasound generally cannot differentiate ruptured from an intact AAA. The distinction is made based on clinical context.

Documentation

Normal Exam

A bedside ultrasound was conducted to assess for AAA with clinical indications of hypotension and lower back pain. The aorta was assessed at 4 locations in the transverse plane – proximal, mid, distal, and aortic bifurcation. Additionally, the distal aorta was viewed in the sagittal plane. No sonographic evidence of AAA at these sites.

Abnormal Exam

A bedside ultrasound was conducted to assess for AAA with clinical indications of hypotension and lower back pain. The aorta was assessed at 4 locations in the transverse plane – proximal, mid, distal, and aortic bifurcation. Additionally, the distal aorta was viewed in the sagittal plane. A 5.5cm AAA was discovered in the distal aorta.

Clips

Ruptured AAA^[4]

External Links

ACEP Focus On: Bedside Ultrasound of the Abdominal Aorta

References

↑ Kuhn M, Bonnin RL, Davey MJ, Rowland JL, et al. Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate, and advantageous. Ann Emerg Med. 2000; 36(3):219-223.
↑ Fojtik JP, Costantino TG, Dean AJ. The diagnosis of aortic dissection by emergency medicine ultrasound. J Emerg Med. 2007; 32(2):191-196.
↑ Tayal VS, et al. Acad Emerg Med, 2003. PMID 12896888
↑ http://www.thepocusatlas.com/aorta-1/

Authors:

[1] Kuhn M, Bonnin RL, Davey MJ, Rowland JL, et al. Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate, and advantageous. Ann Emerg Med. 2000; 36(3):219-223.

[2] Fojtik JP, Costantino TG, Dean AJ. The diagnosis of aortic dissection by emergency medicine ultrasound. J Emerg Med. 2007; 32(2):191-196.

[3] Tayal VS, et al. Acad Emerg Med, 2003. PMID 12896888

[4] ttp://www.thepocusatlas.com/aorta-1/

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