Brain aneurysms are detected through specialized imaging scans that create detailed pictures of the blood vessels in your brain. There is no at-home test or self-check for a brain aneurysm. If you have symptoms or risk factors that concern you, the process starts with your doctor ordering one of several types of vascular imaging, each with different strengths depending on your situation.
Symptoms That Prompt Testing
Most unruptured brain aneurysms cause no symptoms at all, especially when they’re small. This is part of what makes them unsettling: many people who have one never know it until it’s found incidentally during a scan for something else.
A larger unruptured aneurysm can press on surrounding brain tissue and nerves, producing noticeable warning signs. These include pain above and behind one eye, a dilated pupil, double vision or other changes in vision, numbness on one side of the face, or seizures. Any of these symptoms, particularly when they appear suddenly or together, warrant imaging.
The most urgent scenario is a sudden, explosive headache, often described as the worst headache of your life. This “thunderclap headache” can signal a rupture and is a medical emergency. In that case, the diagnostic process happens in the emergency department, not through an outpatient referral.
The Three Main Imaging Tests
CT Angiography (CTA)
CTA is often the first test used, especially in urgent situations. It works by injecting a contrast dye into a vein, then taking rapid X-ray slices of your brain. The dye highlights blood flow through your arteries, making aneurysms visible. CTA is fast, widely available (including overnight in most hospitals), and highly accurate, with a detection sensitivity around 95% for aneurysms. It does involve radiation exposure and iodine-based contrast dye, which can be a concern for people with severe kidney disease or contrast allergies.
MR Angiography (MRA)
MRA uses magnetic fields and radio waves rather than X-rays, so there’s no radiation. It can detect the size, shape, and location of an aneurysm, and its sensitivity has become comparable to CTA in recent years. MRA is the preferred option for routine screening and long-term follow-up because it avoids repeated radiation and contrast dye exposure. The trade-offs: MRA takes longer, may not be available at all hours, and is harder to perform on critically ill patients or those who can’t hold still, since it’s more sensitive to motion artifacts. People with certain metal implants cannot have an MRI.
Cerebral Angiogram (DSA)
Digital subtraction angiography is the most detailed test available. A thin catheter is inserted into an artery, typically in the groin or wrist, and threaded up through the blood vessels to the brain. Contrast dye is injected through the catheter, and a series of X-rays captures extremely precise images of the arteries. Because it’s invasive, a cerebral angiogram is generally reserved for cases where CTA or MRA don’t provide enough information, or when doctors are planning a procedure to treat a known aneurysm.
Emergency Diagnosis After a Thunderclap Headache
If you arrive at an emergency department with a sudden, severe headache, the standard approach is a CT scan of the head within 12 hours of symptom onset. This non-contrast CT can detect bleeding in and around the brain. If the CT looks normal but suspicion remains high, a lumbar puncture (spinal tap) follows. The spinal fluid is tested for traces of blood that would confirm a subarachnoid hemorrhage, even one too small for CT to catch. If blood is found, a CTA or cerebral angiogram pinpoints the aneurysm responsible.
Who Should Be Screened Without Symptoms
Routine screening isn’t recommended for the general population, but certain risk factors change that calculation. Mayo Clinic recommends regular MRI screening for people with a family history of brain aneurysm, particularly those with two or more first-degree relatives who have had an aneurysm or a rupture. Other factors that may qualify you for screening include polycystic kidney disease, connective tissue disorders, and a personal history of smoking combined with family history. If any of these apply to you, raising the question with your doctor is reasonable, as screening MRA is noninvasive and can catch aneurysms long before they become dangerous.
What Happens If an Aneurysm Is Found
Many aneurysms discovered incidentally are small and unlikely to rupture. In these cases, the standard approach is watchful monitoring rather than immediate treatment. Guidelines from the American Heart Association recommend a first follow-up scan 6 to 12 months after the initial discovery, then continued imaging every one to two years once the aneurysm is shown to be stable. For this ongoing surveillance, MRA is generally preferred over CTA to avoid repeated exposure to radiation and contrast dye.
During monitoring, your doctor will look for any change in the aneurysm’s size or shape, which would shift the risk calculation toward intervention. Factors that influence whether treatment is recommended include the aneurysm’s size, its location, your age, your overall health, and whether you have a history of a previous rupture. Treatment options exist, but the decision to intervene is always weighed against the risks of the procedure itself.
How to Prepare for a Brain Vascular Scan
Preparation depends on the type of scan. For an MRA, you’ll be asked about metal implants, pacemakers, or other devices that could interact with the magnetic field. For a CTA, your kidney function may be checked beforehand with a blood test, since the iodine-based contrast dye can worsen kidney problems in people with already impaired function. Women should inform the imaging team if there’s any possibility of pregnancy before any scan involving radiation or contrast.
After a contrast-enhanced scan, you can typically return to normal activities and eating right away. Drinking extra fluids helps your body flush out the contrast material. The scan results are usually read by a radiologist and sent to your ordering doctor within a day or two, though emergency scans are interpreted immediately.