Informational only. This page describes how this condition appears on ultrasound imaging for educational purposes. It is not medical advice, diagnosis, or treatment guidance.
An abdominal aortic aneurysm is a localized dilation of the abdominal aorta, most commonly below the renal arteries. Ultrasound is the first-line screening and surveillance modality — it is fast, radiation-free, and highly accurate for detecting and measuring AAA.
What it is
The abdominal aorta normally measures less than 3 cm in transverse diameter. An aneurysm is defined as a focal dilation greater than 3 cm or more than 50 percent larger than the adjacent normal segment. AAAs are most common in men over 65 with a smoking history; the U.S. Preventive Services Task Force recommends one-time screening ultrasound for men aged 65 to 75 with a history of tobacco use.
The clinical concern is rupture. Mortality from a ruptured AAA exceeds 50 percent overall and approaches 80 percent in patients who reach the hospital alive. Aneurysms that grow past 5.5 cm in men or 5.0 cm in women are typically referred for elective repair before rupture risk climbs steeply.
How it appears on ultrasound
A focused AAA screening exam takes minutes. The patient lies supine; the sonographer images the aorta from the diaphragm to the bifurcation in transverse and longitudinal planes, measuring the maximum outer-wall-to-outer-wall diameter at multiple levels. A normal aorta tapers smoothly distally; an aneurysm shows a focal saccular or fusiform dilation, often with mural thrombus layered along the wall.
Mural thrombus appears as low-level echogenic material lining the inside of the dilated segment, with the residual flow lumen seen in the center on color Doppler. Thrombus is clinically meaningful because the residual flow lumen — not the outer wall — is what feels “open,” but it is the outer-wall measurement that determines rupture risk and surgical timing.
Surveillance intervals follow the diameter. Aneurysms 3.0 to 3.9 cm are typically rescanned every two to three years; 4.0 to 4.9 cm annually; 5.0 to 5.4 cm every six months. Above the surgical threshold, imaging guides operative or endovascular planning rather than ongoing observation.
Ultrasound’s main limitation is bowel gas, which can obscure the aorta in some patients — particularly the distal portion approaching the bifurcation. CT angiography is the next imaging step when ultrasound is non-diagnostic and is the standard for surgical planning.
Which specialty images it
Vascular sonography handles AAA screening, surveillance, and follow-up of endovascular repairs. Some general abdominal sonographers also perform basic AAA measurements as part of complete abdominal exams. Point-of-care ultrasound (POCUS) by emergency physicians has become routine for ruling in suspected ruptured AAA in unstable patients. See the vascular specialty page for credential and scope details.