A saccular AAA is seen as a hypoechoic pouch off the aortic wall. Notice the images below and how only the anterior abdominal aorta is involved with a saccular appearance in the long axis.
A fusiform AAA is seen as widening of the aortic diameter ≥3cm.
Abdominal aortic aneurysms occur when a weakness in the artery’s connective tissue media (usually due to arteriosclerosis) results in a pathologic dilatation of the aorta.
A normal aorta is usually ~2.0cm in diameter. An abdominal aortic aneurysm is defined as: (Mokashi)
- ≥ 3cm diameter for the abdominal aorta or a > 50% increase in the aortic diameter.
- ≥ 1.5cm diameter for the iliac arteries.
Aneurysms can be morphologically classified as either fusiform or saccular. Fusiform aneurysms are symmetrical, circumferential dilatations of a vessel – they are far more common than saccular aneurysms, but less likely to cause symptoms (Faluk). Saccular aneurysms form as asymmetrical outpocketings of the aortic wall.
AAA can be further classified by location as either suprarenal or infrarenal – above or below the renal arteries. Infrarenal AAA is much more common, representing ~85% of cases (Kent).
Ultrasound identification of AAA has a sensitivity and specificity >90% (Fleming), so learning to use it properly can reliably diagnose this life-threatening disease process.
Use the techniques described above to scan the abdominal aorta and measure its diameter in 3 sections (proximal, mid, and distal).
- Keep the aorta in view at all times as you descend, and be careful to note any widening.
- Tip: a mural thrombus can disguise itself as the outer wall and falsely reduce your diameter measurement. Be sure to measure the outer to outer walls and therefore including the thrombus in the diameter measurement.