An aortic aneurysm is most often diagnosed with an ultrasound, a painless imaging test that can detect a bulging aorta with roughly 98% accuracy. Many aneurysms produce no symptoms at all, so the diagnosis frequently happens either through routine screening or by accident, when imaging done for an unrelated reason reveals a widened aorta. An abdominal aorta measuring 3 cm (about 30 mm) or more in diameter meets the threshold for an aneurysm.
What a Physical Exam Can and Cannot Find
During a physical exam, a doctor may press on your abdomen to feel for a pulsating mass near the belly button and listen with a stethoscope for unusual rushing sounds (called bruits) along the path of the aorta and the arteries in your groin. When an aneurysm is large, it can feel like a strong, rhythmic throb under the skin. A doctor who suspects something abnormal will estimate the width of the aorta by hand and refer you for imaging.
Physical exams alone are not reliable for catching aneurysms. Detection depends heavily on both the size of the aneurysm and the patient’s body type. When a patient’s waist circumference is 100 cm (about 40 inches) or more, very few aneurysms can be felt by hand. Smaller aneurysms in thinner patients may also escape notice. One study of ruptured aneurysms found that a pulsatile mass was felt in only 26% of patients who were initially misdiagnosed, compared to 72% of those correctly identified. The most common misdiagnoses were kidney stones, diverticulitis, and gastrointestinal bleeding, because the symptoms of abdominal pain, back pain, and shock overlap so much.
Ultrasound: The First-Line Test
Abdominal ultrasound is the standard first test for detecting an aortic aneurysm. It uses sound waves to create a live image of the aorta, requires no radiation, and involves no needles or contrast dye. A meta-analysis of ultrasound studies found a pooled sensitivity of 97.5% and specificity of 98.9% for detecting abdominal aortic aneurysms, making it one of the most accurate screening tools in medicine.
For the clearest images, you’ll typically be asked to fast overnight before the exam and avoid tobacco and caffeine beforehand. A technician applies gel to your abdomen and moves a handheld probe across your skin. The full exam can take up to an hour, though many are shorter. There is no pain involved, and results are usually available the same day or within a few days.
Ultrasound works well for measuring the width of the abdominal aorta and tracking whether a known aneurysm is growing over time. It is less useful for the thoracic aorta (the portion in your chest), because the ribs and lungs interfere with the sound waves.
CT Angiography for Detailed Planning
When a doctor needs more precise measurements or is planning a repair procedure, CT angiography (CTA) is the go-to test. A CT scanner takes rapid X-ray images while contrast dye flows through your bloodstream, producing detailed cross-sectional pictures of the entire aorta, from the chest through the abdomen and into the pelvis.
CTA shows not just the diameter of the aneurysm but also its exact shape, its relationship to nearby arteries (like those feeding the kidneys), and whether there are complications such as blood clots within the aneurysm wall or signs of leaking. For patients who have already had an endovascular stent graft placed, a delayed scan after the initial contrast injection can check for endoleaks, where blood seeps around the graft.
For thoracic aortic aneurysms specifically, CTA of the chest, abdomen, and pelvis is considered the most appropriate imaging before surgical repair. The scan itself takes only a few minutes, though you may spend 15 to 30 minutes in the facility for preparation and the IV line for contrast dye. The main downsides are radiation exposure and the contrast dye, which can be a concern for people with kidney problems or dye allergies.
MRI and MR Angiography
Magnetic resonance imaging offers an alternative when CT isn’t ideal. MRI uses magnetic fields instead of radiation, making it a better option for younger patients who may need repeated scans over many years or for anyone who cannot receive iodine-based contrast dye. MRI can evaluate both the aortic wall and the blood flowing through it using different imaging sequences. One significant advantage is that certain MRI techniques can produce clear images of arteries without any contrast agent at all, which is useful for patients with impaired kidney function.
MRI is particularly good at visualizing the thoracic aorta. It can assess heart valve structure and function at the same time, which matters because some conditions that cause thoracic aneurysms also affect the aortic valve. The tradeoff is that MRI scans take longer (often 30 to 60 minutes), require you to lie still inside a narrow tube, and are less widely available on an emergency basis than CT.
Echocardiography for the Upper Aorta
An echocardiogram, which is essentially an ultrasound of the heart, can visualize the first portion of the aorta as it leaves the heart (the aortic root and ascending aorta). This is often how aneurysms near the heart are first spotted, since echocardiograms are commonly ordered for other cardiac concerns. If the echocardiogram suggests a dilated aorta, your doctor will typically follow up with a CT or MRI to get a complete picture of the thoracic aorta.
Screening Recommendations
The U.S. Preventive Services Task Force recommends a one-time abdominal ultrasound screening for men aged 65 to 75 who have ever smoked. This is a “B” recommendation, meaning there is good evidence that the benefit of screening outweighs the harms. Smoking is the strongest risk factor for abdominal aortic aneurysms, and men develop them far more often than women.
There is no similar blanket recommendation for women or for people who have never smoked, though doctors may suggest screening on a case-by-case basis for people with other risk factors, including a family history of aneurysms or a history of high blood pressure.
Aneurysms Found by Accident
A large number of aortic aneurysms are discovered incidentally, during imaging ordered for something else entirely. A study of nearly 2,000 patients who received lumbar spine MRIs found that 4.4% had an abdominal aorta measuring 30 mm or larger, qualifying as an aneurysm. Many of these patients had no idea their aorta was enlarged.
This is actually how most small aneurysms come to light, since they rarely cause symptoms until they grow large or rupture. CT scans done for back pain, kidney stones, or other abdominal complaints routinely capture images of the aorta, giving radiologists a chance to flag unexpected findings. If an incidental aneurysm is found, the next step is usually a dedicated ultrasound or CTA to get precise measurements and establish a baseline for monitoring.
What the Measurements Mean
A normal abdominal aorta is roughly 2 cm in diameter. An aorta measuring 3 cm or more is classified as aneurysmal. Once diagnosed, the size of the aneurysm determines what happens next. Small aneurysms (typically under 5 to 5.5 cm) are monitored with periodic ultrasounds, often every 6 to 12 months, to track growth. Larger aneurysms or those growing rapidly are evaluated for surgical repair.
For thoracic aneurysms, the thresholds are somewhat higher because the thoracic aorta is naturally wider than the abdominal aorta. Consistency in measurement technique matters: doctors compare scans taken the same way, at the same point in the cardiac cycle when possible, to avoid falsely concluding that an aneurysm has grown. ECG-gated CT scans, which synchronize imaging with the heartbeat, help ensure measurements are comparable from one visit to the next.