Aortic ultrasound

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Background

  • Aortic ultrasound should be utilized to assess for aneurysm or dissection
  • Aneurysm is defined as 3cm (150% the upper limit of normal)
  • 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

  1. Select probe
    • Curvilinear/large convex probe (phased array probe may substitute)
  2. 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
  3. Transverse views
    1. Proximal aorta
    2. Mid-aorta
    3. Distal aorta
    4. Aortic bifurcation
  4. 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
  • Abdominal aortic dissection can be identified as an intimal flap

Images

Normal

Normal Aorta.JPG

Abnormal

Abdominal Aortic Aneurysm

AAA.png AAA2.png

Aortic Dissection

Type B Dissection.png

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

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

Celiac and SMA identified Aortic bifurcation

External Links

See Also

References

  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.

Authors

Neil Young