Ultrasound Teaching Atlas
Draft — not yet peer-reviewedcoreAbdomen / RetroperitoneumAorta

Abdominal Aorta (AAA Screening)

Scan the aorta from epigastrium to bifurcation and measure it to screen for abdominal aortic aneurysm.

This module is a content/teaching-structure draft. Images shown are illustrative schematics — real, de-identified, license-verified ultrasound clips replace them before peer review.

Learning objectives

  • Identify the aorta versus the IVC using position, wall, and compressibility.
  • Scan the aorta in short axis from the epigastrium to the iliac bifurcation.
  • Measure the maximal AP diameter outer-wall to outer-wall and apply the AAA threshold.

Maps to

  • Resident: ACEP Emergency Ultrasound — Aorta: Image Acquisition
  • Resident: ACEP Emergency Ultrasound — Aorta: AAA measurement
  • Tech: ARDMS Abdomen (AB) — aorta and AAA

Acquisition — getting the view

Probe
curvilinear
Patient position
Supine, knees flexed to relax the abdominal wall.
Orientation convention
radiology
Probe placement
Midline epigastrium, swept caudally to the umbilicus
Marker direction
Indicator to patient's right (transverse / short axis)

Probe placement (3D)

Midline epigastrium, swept caudally to the umbilicus

Structures in the imaging plane (near → far): Abdominal wall · Bowel (gas may obscure) · Inferior vena cava (to patient's right) · Abdominal aorta · Vertebral body (posterior shadow)

Step by step

  1. Place the curvilinear probe transverse in the epigastrium, indicator to the patient's right. Identify the vertebral body shadow.
    Why: The aorta sits just anterior and to the patient's left of the spine; the IVC is to the right.
  2. Apply steady graded pressure to displace bowel gas and sweep caudally to the bifurcation.
    Why: Aneurysms are most common infrarenally, near the bifurcation.
  3. Rotate 90° to long axis to confirm and look for thrombus.
    Why: Confirms diameter and avoids missing a focal aneurysm.

Troubleshooting

Bowel gas blocks the view.
Apply slow, steady pressure to displace gas, or use the liver as a window superiorly.
Unsure if the vessel is aorta or IVC.
The aorta is thick-walled, pulsatile, non-compressible, and left of midline; the IVC is thin-walled and compressible.

Findings: normal

Normal aorta

A round, thick-walled, pulsatile vessel anterior to the spine measuring less than 3 cm.

Schematic of a normal abdominal aorta in short axis
Schematic: normal aorta (< 3 cm) anterior to the vertebral body.
Original schematic, dedicated to the public domain (CC0).

Findings: pathology

Abdominal aortic aneurysm (AAA)

Focal dilation of the aorta to ≥ 3.0 cm (outer-wall to outer-wall). Mural thrombus may line the lumen — measure the true outer diameter, not just the flow channel.

Signs: Outer diameter ≥ 3 cm; Mural thrombus narrowing the lumen

Schematic of an abdominal aortic aneurysm with thrombus
Schematic: AAA with mural thrombus; measure outer-to-outer.
Original schematic, dedicated to the public domain (CC0).

Interpretation practice

You measure a round retroperitoneal vessel anterior to the spine at 3.6 cm outer-to-outer. What is the finding?

Enlarged aorta measured in short axis
Outer diameter 3.6 cm — interpret.
Original schematic, dedicated to the public domain (CC0).

Measurement practice

Measure the maximal anteroposterior aortic diameter, outer-wall to outer-wall.

Aorta short axis with calipers for AP diameter
Place calipers outer-wall to outer-wall, perpendicular to the vessel.
Original schematic, dedicated to the public domain (CC0).
cm

Check your understanding

What is the diameter threshold for diagnosing an AAA?

Why measure outer-wall to outer-wall rather than the lumen?

References

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