Aneurysms are diagnosed primarily through imaging, not blood tests or physical exams. The specific type of imaging depends on where the aneurysm is suspected: ultrasound for the abdominal aorta, CT or MRI for the brain and thoracic aorta, and echocardiography for the aortic root. Most aneurysms produce no symptoms and are discovered incidentally during scans ordered for unrelated reasons, which makes understanding screening criteria just as important as knowing the diagnostic tools.
How Brain Aneurysms Are Found
Unruptured brain aneurysms rarely cause symptoms. They’re typically spotted on a CT or MRI scan done for something else entirely, like investigating headaches, dizziness, or head trauma. When a doctor specifically suspects a brain aneurysm, the two main non-invasive options are CT angiography (CTA) and MR angiography (MRA). Both involve injecting contrast dye to highlight blood vessels, though some MRA techniques work without contrast.
The gold standard for confirming a brain aneurysm is digital subtraction angiography (DSA), a procedure where a thin catheter is threaded through a blood vessel (usually starting in the groin) up to the brain’s arteries. DSA produces the most detailed images of blood vessel anatomy and is the benchmark against which other methods are measured. However, because it’s invasive and carries a small risk of complications, it’s typically reserved for cases where non-invasive imaging is inconclusive or when treatment planning requires precise detail.
CTA is the workhorse for initial diagnosis. It’s fast, widely available, and provides high-resolution 3D images. MRA is better suited for situations where radiation exposure is a concern or when repeated scans are needed over time, since MRI uses no ionizing radiation. Both TOF-MRA and contrast-enhanced MRA have pooled sensitivity and specificity around 85 to 88 percent for detecting changes in previously treated aneurysms, according to a meta-analysis in the American Journal of Neuroradiology.
How Aortic Aneurysms Are Diagnosed
The aorta, your body’s largest artery, can develop aneurysms in two main locations: the abdomen and the chest. Each has a somewhat different diagnostic pathway.
Abdominal Aortic Aneurysm
An abdominal aortic aneurysm (AAA) is diagnosed when the abdominal aorta measures 3 centimeters or larger in diameter. The normal diameter is roughly 2 centimeters, so a diagnosis requires the vessel to have expanded by about 50 percent. Ultrasound is the primary tool for both screening and diagnosis. It’s painless, takes about 15 minutes, requires no radiation, and is highly accurate for measuring aortic diameter.
If an AAA is confirmed, CT angiography is often used to get more detailed information about the aneurysm’s exact shape, its relationship to nearby blood vessels, and whether it’s suitable for repair. This level of detail matters for treatment planning but isn’t usually needed for the initial diagnosis itself.
Thoracic Aortic Aneurysm
Thoracic aortic aneurysms (those in the chest) are harder to detect because ultrasound can’t image that portion of the aorta as easily. Transthoracic echocardiography, a standard heart ultrasound, is the most common first-line tool and works well for visualizing the aortic root and ascending aorta. But for a complete picture of the thoracic aorta, CT or MRI is needed.
CT scanning has become the dominant imaging method for thoracic aortic disease. It can image the entire aorta and its branches with high spatial resolution in a matter of seconds. When synchronized with the heartbeat (a technique called ECG-gated CT), it reduces motion blur near the heart and significantly improves measurement accuracy. MRI offers comparable detail without radiation, making it a strong option for younger patients or anyone who needs serial imaging over years. Many thoracic aortic aneurysms are found incidentally on chest CT scans ordered for other reasons, such as evaluating lung problems or chest pain.
Screening: Who Should Be Checked Before Symptoms Appear
Because aneurysms are often silent until they rupture, screening specific high-risk groups is a key part of diagnosis.
For abdominal aortic aneurysms, the U.S. Preventive Services Task Force recommends a one-time ultrasound screening for men aged 65 to 75 who have ever smoked. Men in that age range who have never smoked may also benefit from screening depending on other risk factors, while the evidence for routine screening in women is less clear.
For brain aneurysms, screening is generally recommended when you have two or more first-degree relatives (parents, siblings, or children) who have had a brain aneurysm, or one first-degree relative plus one or more second-degree relatives (aunts, uncles, grandparents) who have been affected. Identical twins of someone with a brain aneurysm are also candidates for screening. Weaker family histories don’t typically warrant screening because the overall risk remains low and the downsides of unnecessary testing, including anxiety and potential follow-up procedures, outweigh the benefits.
For thoracic aortic aneurysms, the American Heart Association recommends that first-degree relatives of anyone with an aortic root or ascending aortic aneurysm, or anyone who has had an aortic dissection, undergo aortic imaging to check for unrecognized disease. Certain genetic conditions, including Marfan syndrome and Loeys-Dietz syndrome, also place people in a high-risk screening category.
What Happens After an Aneurysm Is Found
Not every aneurysm requires immediate treatment. Many small, unruptured aneurysms are monitored over time with repeat imaging to see whether they grow. For unruptured brain aneurysms, the typical approach is a first follow-up scan 6 to 12 months after the initial discovery. If the aneurysm remains stable at that point, imaging shifts to once a year or every two years. The goal is to catch any growth early enough to intervene before the risk of rupture becomes significant.
Small abdominal aortic aneurysms follow a similar surveillance pattern. An AAA between 3 and 4 centimeters is usually rechecked with ultrasound every two to three years. Between 4 and 5 centimeters, scans happen more frequently, typically every 6 to 12 months. Repair is generally considered when the aneurysm reaches 5 to 5.5 centimeters or is growing rapidly.
During monitoring, your doctor will also focus on controlling risk factors that accelerate aneurysm growth: high blood pressure, smoking, and high cholesterol. Quitting smoking is the single most impactful change you can make, as smoking is both a major cause of aortic aneurysms and a driver of faster expansion.
Can a Blood Test Detect an Aneurysm?
There is no blood test currently approved to diagnose aneurysms. Imaging remains the only reliable method. However, research is moving toward blood-based screening tools. A collaboration between Cleveland Clinic and the University of Cincinnati identified a platelet protein called GPVI as a promising biomarker for abdominal aortic aneurysms. In studies published in the journal Blood, GPVI levels were highly predictive of an AAA diagnosis and correlated with how fast the aneurysm was growing, which is critical for assessing risk. A follow-up trial of about 300 patients with known AAA confirmed these findings.
Researchers envision a future screening panel combining several biomarkers that could be used routinely in patients over 50 to catch AAA before it becomes dangerous. For now, though, this remains a research tool rather than something available in clinical practice.
Ruptured Aneurysm: Emergency Diagnosis
When an aneurysm ruptures, diagnosis shifts to emergency mode. A ruptured brain aneurysm typically causes a sudden, severe headache often described as the worst of your life, along with nausea, vomiting, stiff neck, blurred vision, or loss of consciousness. A non-contrast CT scan of the head is the first test performed because it can detect bleeding in and around the brain within minutes. If the CT is negative but suspicion remains high, a lumbar puncture (spinal tap) may be done to check for blood in the spinal fluid.
A ruptured abdominal aortic aneurysm causes sudden, severe pain in the abdomen or back, often with lightheadedness or fainting from internal blood loss. CT angiography is the fastest way to confirm the diagnosis in the emergency department. In both cases, the priority is speed: confirmed ruptures require emergency surgical intervention.