Abdominal Aortic Aneurysm (AAA): Ultrasound as a Lifesaving Screening Method

Dr. Segnini
Jan 1
4 min read

Dr. Segnini Abdominal aortic aneurysm ultrasound

The Silent Killer in the Abdomen

An abdominal aortic aneurysm (AAA) is an abnormal and permanent dilation of the aorta in its abdominal segment, with a diameter exceeding its normal size (generally >3 cm) by more than 50%. Its danger lies in the fact that it is asymptomatic in the vast majority of cases until a catastrophic complication occurs: dissection or rupture , which carries an extremely high mortality rate. Abdominal ultrasound is the gold standard method for screening, diagnosis, and monitoring due to its accuracy, safety, and accessibility.

Why is ultrasound the ideal technique for AAA?

Ultrasound is the perfect tool for evaluating the aorta for several critical reasons:

High Precision: It is highly sensitive and specific for detecting and measuring AAA, with millimeter accuracy.
Absolute Safety: It does not use ionizing radiation or intravenous contrast media, allowing for repeated use for follow-up.
Quick and Accessible: The test takes only a few minutes and is available at most health centers.
Cost-Effective: It is significantly cheaper than Computed Tomography (CT), ideal for population screenings.
Direct Visualization: Allows you to view the aorta in real time, evaluate its morphology and measure its diameter with great accuracy.

Key Ultrasound Findings: Beyond Simple Measurement

1. Primary Finding: Aortic Dilation

Normal Anatomy: The normal abdominal aorta is visualized as an anechoic (black) tubular structure with hyperechoic (bright) and parallel walls. Its diameter decreases progressively from the aortic hiatus of the diaphragm (≈2.5 cm) to its bifurcation into the iliac arteries (≈1.5-2 cm).
Definition of AAA: It is diagnosed when the maximum anteroposterior (transverse) diameter of the aorta, measured in cross-section, exceeds 3.0 cm . The measurement must be external to external (wall to wall), perpendicular to the long axis of the vessel, at its most dilated portion.

2. Characterization of the Aneurysm:

Shape:
- Fusiform: Symmetrical dilation that affects the entire circumference of the aortic wall. It is the most common type.
- Saccular : Localized and asymmetrical dilation that projects like a "sac" from one side of the aorta.
Location: The majority (≈95%) are infarrenal (below the origin of the renal arteries). Identifying the relationship to the renal arteries and the iliac bifurcation is crucial for planning any potential repair.
Presence of Mural Thrombi: It is very common to see a hypoechoic (gray) or heterogeneous accumulation within the aneurysmal lumen , adhered to the wall , which corresponds to a thrombus. Ultrasound clearly differentiates the lumen patente ( anea). anechoic ( through which blood flows) of the mural thrombus . The total diameter (including thrombus) and the lumen diameter are measured .

3. Warning Signs of Instability or Imminent Rupture (Emergency Findings):

Painful Aneurysm on Pressure: Reproducible pain when pressure is applied with the transducer over the aneurysm.
Donald 's sign " or Retroperitoneal Hematoma: Presence of fluid or echogenic material (blood) in the retroperitoneal space, typically around the AAA. It is a sign of contained rupture.
Free Intraperitoneal Hematoma: Free blood in the abdomen, indicative of free rupture, an extremely serious situation.
Accelerated Growth: An increase of more than 0.5-1.0 cm in one year is a major risk factor for rupture.

Exploration and Measurement Protocol

The exam is systematic:

Identification: The aorta is located in longitudinal (sagittal) section at the level of the midline, identifying it by its location anterior to the vertebral bodies and to the left of the inferior vena cava.
Transverse (Axial) Measurement: This is the most important and reproducible measurement . The transducer is slid from the epigastrium to the bifurcation, locating the maximum diameter . The image is frozen and the measurement is taken from outer wall to outer wall.
Longitudinal Section Evaluation: To confirm the extent, the relationship with the renal arteries (identified by their lateral origin) and the iliac bifurcation.
Color Doppler (Optional, but useful): To confirm flow in the lumen patentee , assess the patency of the iliac arteries and rule out fistulas.

Ultrasound in Population Screening

Based on its effectiveness, single ultrasound screening is recommended for:

Men aged 65 to 75 who have ever smoked.
Men and women aged 65 to 75 with a family history of AAA in first-degree relatives.

This screening has been shown to significantly reduce mortality from AAA rupture .

Ultrasound vs. Computed Tomography (CT)

Ultrasound: It is the method of choice for screening, initial diagnosis, and follow-up . Its accuracy in measuring diameters is excellent.
Computed Tomography (CT Angiography ): This is reserved for pre-surgical or endovascular planning . It provides an accurate three-dimensional view of the anatomy, the relationship with the renal and accessory arteries, and the quality of the access vessels (iliac arteries). It is used when intervention is decided upon .

Conclusion: Non-Invasive Surveillance that Prevents Disasters

Abdominal ultrasound has transformed the management of abdominal aortic aneurysms (AAAs) from an often fatal disease to a condition that can be safely monitored and treated electively . Its role as a population screening tool is irreplaceable, allowing for the detection of asymptomatic aneurysms. As a follow-up method , it guides clinical decisions based on size and growth rate, determining the optimal time for repair (generally when it exceeds 5.0–5.5 cm or is growing rapidly). In essence, ultrasound is the silent guardian that prevents aortic rupture, saving countless lives through a simple, quick, and safe examination.