What does it mean to have multiple brain aneurysms?

EMERGENCY WARNING: If you or a loved one experience a sudden, severe “worst-ever” headache—especially if it is accompanied by vomiting, a stiff neck, fainting, a seizure, confusion, weakness, numbness, trouble speaking, or vision loss—call emergency services (911) immediately. These can be signs that an aneurysm has ruptured (burst). Do not wait for a scheduled scan or drive yourself to the hospital.

Finding out you have more than one brain aneurysm can be frightening, but it is actually quite common. About 15% to 35% of people diagnosed with an unruptured brain aneurysm are found to have multiple aneurysms ^[1]. Having more than one aneurysm does increase your aggregate, overall risk compared to having just one, but it does not mean that every aneurysm is highly dangerous or about to rupture ^[2].

Instead, a cerebrovascular specialist or multidisciplinary team will evaluate each aneurysm individually. They will prioritize treatment for any high-risk lesions while safely monitoring those that pose a lower risk ^[3]. Having multiple aneurysms also means you will need long-term imaging follow-up to watch for changes and highlights the importance of managing lifestyle factors and assessing your family history.

How Your Care Team Evaluates Each Aneurysm

When multiple aneurysms are present, a complete and detailed map of your brain’s blood vessels is essential. Doctors use advanced imaging to identify exactly how many aneurysms you have and to examine the specific features of each one.

• Non-Invasive Scans: A CTA (computed tomography angiography) or an MRA (magnetic resonance angiography) is typically used as a first-line test to detect and measure aneurysms ^[4]. These tests are usually alternatives to each other rather than combined; MRA avoids radiation and iodine contrast, while CTA may be used if you have implants or cannot tolerate an MRI.
• Detailed Mapping: In some cases, your doctor may recommend a DSA (digital subtraction angiography). This is an invasive catheter procedure guided to the brain’s blood vessels. While it is the most definitive way to map aneurysms because of its extremely high resolution, it carries small but important risks, including stroke, bleeding at the puncture site, and contrast-related kidney injury ^[4][5]. DSA is not routine for everyone; it is used selectively when scan results are inconclusive or for detailed treatment planning.

Risk Is Assessed Aneurysm by Aneurysm

Not all aneurysms carry the same risk. Rather than assuming all your aneurysms are equally dangerous, your cerebrovascular team will estimate the risk for each one individually ^[6].

Factors that influence the risk of a specific aneurysm include:

• Size and Shape: Larger aneurysms are generally riskier, but the shape is heavily factored into the decision. An aneurysm with an irregular shape, a high aspect ratio (meaning its height is large relative to the width of its opening or “neck”), or a “daughter sac” (a small blister on the aneurysm) has a higher risk of rupturing ^[6][7][8].
• Location: Aneurysms located in certain blood vessels, such as the posterior circulation (arteries at the back or base of the brain), may carry a higher risk of rupture ^[9].
• Growth: An aneurysm that is actively growing is a major warning sign. Research shows that growing aneurysms have a significantly higher risk of rupture compared to those that remain stable ^[10][11].

If you have already experienced a ruptured aneurysm (a subarachnoid hemorrhage, which is bleeding into the space around the brain), identifying and securing the specific aneurysm that bled is the immediate medical priority ^[12]. Once the ruptured aneurysm is treated, your team will evaluate the remaining unruptured aneurysms.

Prioritizing Treatment and Monitoring

Your medical team will weigh the estimated rupture risk of each aneurysm against your age, overall health, life expectancy, and the risks of the treatment procedure itself ^[3].

• Individualized Treatment Decisions: Doctors often prioritize treating the aneurysm with the highest-risk features, which might not necessarily be the largest one ^[7]. Treatment options include surgical clipping, endovascular coiling, or using devices like flow diverters and stents. The order of treatment also depends on your anatomy and whether multiple aneurysms can safely be treated during a single procedure.
• Active Monitoring (Surveillance): Aneurysms that are small, smooth, and stable may not require immediate treatment ^[3]. Instead, they are managed through active observation with regular MRA or CTA scans ^[13]. There is no single “correct” schedule for scans; your interval will depend on the aneurysm’s size, location, prior growth, and your kidney function. While choosing observation is an active medical strategy rather than “doing nothing,” the uncertainty and repeated scans can be emotionally difficult.
• Recurrence and New Aneurysms: Long-term follow-up is necessary because multiple aneurysms indicate your blood vessels may be prone to forming them. Treated aneurysms can sometimes recur (which is more common after certain endovascular treatments than after clipping), and while uncommon, completely new (de novo) aneurysms can form years later ^[14][15].

Taking Control: Lifestyle and Family History

Having multiple aneurysms points to an underlying vulnerability in the blood vessels, making proactive health management an important part of your care.

• Blood Pressure Management: High blood pressure (hypertension) is strongly associated with the formation of aneurysms and overall vascular health ^[16][17]. Work with your doctor to determine your individualized target blood pressure range and do not change medications without consulting them. Measuring your blood pressure at home can help you stay on track.
• Quitting Smoking: Smoking is a major risk factor associated with a higher rate of aneurysm growth and the formation of new aneurysms ^[18][10]. Quitting smoking lowers (though it does not entirely eliminate) these risks. It is one of the most effective steps you can take, and your doctor can help connect you with cessation support programs.
• Genetic Risk and Screening: Having multiple aneurysms does not automatically mean you have an inherited genetic disorder ^[19]. However, they can sometimes be linked to conditions like Autosomal Dominant Polycystic Kidney Disease (ADPKD, an inherited kidney and liver cyst condition) or a strong family history ^[20]. If two or more of your first-degree relatives (parents, siblings, or children) have had a confirmed brain aneurysm or aneurysmal subarachnoid hemorrhage, guidelines recommend discussing screening for your relatives ^[21][22]. Unexplained strokes do not automatically count; the aneurysms must be confirmed.