Most aneurysms are detected in one of three ways: emergency imaging after sudden symptoms, screening tests for people at higher risk, or accidentally during a scan done for something else entirely. The detection method depends on where the aneurysm is, whether it has ruptured, and whether you have risk factors that qualify you for proactive screening.
Because aneurysms can form in different arteries, there is no single test that catches them all. Brain aneurysms, abdominal aortic aneurysms, and thoracic aortic aneurysms each have their own detection tools and screening criteria.
Many Aneurysms Are Found by Accident
A large number of unruptured aneurysms produce no symptoms at all, especially when they’re small. They show up on brain or body scans ordered for completely unrelated reasons: a head injury, chronic migraines, dizziness, or presurgical imaging. In one study of over 1,100 CT angiograms, about 4% flagged a possible unruptured brain aneurysm. These incidental discoveries have become more common as imaging technology improves and more people get scans.
Finding an aneurysm this way is not necessarily alarming. Many small, unruptured aneurysms are monitored over time with periodic imaging rather than treated immediately. But it does mean the aneurysm gets tracked before it becomes dangerous.
Warning Signs That Trigger Testing
An unruptured brain aneurysm that grows large enough can press on surrounding brain tissue and nerves. When that happens, it can cause pain above and behind one eye, a dilated pupil, double vision or other vision changes, numbness on one side of the face, or seizures. These symptoms typically prompt a doctor to order brain imaging, which is how many aneurysms are caught before they rupture.
Thoracic aortic aneurysms (in the chest) and abdominal aortic aneurysms (in the belly) are harder to detect by symptoms alone. Thoracic aneurysms in particular often produce no signs at all and are difficult to diagnose without imaging.
The “Worst Headache of Your Life”
A ruptured brain aneurysm produces a very specific type of headache called a thunderclap headache. It reaches maximum intensity in less than one minute. People who experience it often describe it as an explosion inside the head or being struck in the head. It is clearly different from any headache they’ve had before. About 70% of people with a ruptured brain aneurysm (subarachnoid hemorrhage) present with headache as their main symptom, and roughly half of those experience this thunderclap pattern.
The headache alone isn’t the only clue. A ruptured aneurysm can also cause an altered level of consciousness, seizures, vision problems, neck stiffness, weakness on one side of the body, or sensory disturbances. Some people experience a “sentinel headache,” a sudden severe headache days or weeks before the full rupture, which represents a critical window for detection if recognized.
Imaging Tests for Brain Aneurysms
Three main imaging tools detect brain aneurysms, and doctors choose between them based on the clinical situation.
- CT angiography (CTA) is the most common first-line test in emergency settings. It’s fast and widely available, making it the go-to when a ruptured aneurysm is suspected. If the CT doesn’t show bleeding but suspicion remains high, a sample of cerebrospinal fluid (the liquid surrounding the brain and spinal cord) can confirm or rule out a rupture.
- MR angiography (MRA) uses magnetic imaging to capture detailed pictures of the brain’s arteries without radiation. It can identify the size, shape, and location of an aneurysm and is often used for screening or monitoring known aneurysms over time.
- Cerebral angiogram is the most detailed test. A thin tube is threaded through a blood vessel, past the heart, and into the brain’s arteries. A contrast dye is injected and X-rays capture a highly detailed map of the blood vessels. This test is typically reserved for cases where CTA or MRA doesn’t provide enough information, or when planning for treatment.
Screening for Abdominal Aortic Aneurysms
The abdominal aortic aneurysm is the only type with a formal population-level screening recommendation in the United States. The U.S. Preventive Services Task Force recommends a one-time ultrasound screening for men aged 65 to 75 who have ever smoked. “Ever smoked” is defined as having smoked 100 or more cigarettes in a lifetime. For men in the same age range who have never smoked, screening is offered selectively based on other risk factors rather than routinely.
For women, the picture is less clear. The task force recommends against routine screening for women who have never smoked and have no family history. For women aged 65 to 75 who have smoked or have a family history, there isn’t enough evidence yet to make a firm recommendation either way.
The screening itself is simple: an abdominal ultrasound that takes about 10 to 15 minutes. It’s painless, requires no preparation, and only needs to be done once if results are normal.
Detection of Thoracic Aortic Aneurysms
Thoracic aortic aneurysms, which form in the section of the aorta running through the chest, have no routine screening program for the general population. They are most often found when imaging is done for another reason entirely.
When a thoracic aneurysm is suspected or needs monitoring, an echocardiogram (heart ultrasound) is a common tool. A standard echocardiogram performed from outside the body can visualize the aorta. If more detail is needed, a transesophageal echocardiogram provides a closer view by imaging from inside the body through the esophagus. CT and MRI scans are also used for precise measurements.
Who Should Be Screened Proactively
Beyond the age-and-smoking criteria for abdominal aneurysms, family history is the strongest reason to pursue screening for brain aneurysms. Having two or more first-degree relatives (parents, siblings, children) who have had a ruptured brain aneurysm raises your risk by roughly 6.6 times compared to the general population. People with this family history are candidates for screening with MRA, even without symptoms.
Certain genetic conditions also increase aneurysm risk across multiple locations. People with connective tissue disorders, polycystic kidney disease, or a known family pattern of aortic disease are often monitored with periodic imaging. For aortic aneurysms, surgical thresholds are adjusted based on genetics, sex, and body size, so detection in these groups tends to happen at smaller aneurysm sizes.
What Happens After Detection
Once an aneurysm is found, the next step depends on its size, location, and whether it’s growing. Small, stable aneurysms are often monitored with repeat imaging every 6 to 12 months. Your doctor will track the diameter over time to watch for growth.
Size matters for treatment decisions. For aortic aneurysms, surgical repair has traditionally been considered when the aneurysm reaches about 5.5 centimeters. Recent guidelines have lowered that threshold to 5.0 centimeters at experienced surgical centers, and even lower for people with inherited connective tissue conditions. The exact threshold is personalized based on your height, sex, and genetic profile.
For brain aneurysms, treatment decisions weigh the aneurysm’s size and shape against the risks of intervention. Many small brain aneurysms (under 7 millimeters) in low-risk locations are safely watched rather than treated. Larger or irregularly shaped aneurysms, or those in high-risk locations, are more likely to be repaired through minimally invasive catheter-based procedures or surgery.