What Is My Personal Unruptured Brain Aneurysm Rupture Risk?

⚠️ EMERGENCY WARNING: If you or a loved one experience a sudden, “worst-ever” thunderclap headache—especially if accompanied by vomiting, stiff neck, loss of consciousness, seizure, or new weakness, numbness, or vision changes—call local emergency services immediately. Do not wait for your next scan. These can be signs of a rupture.

Finding out the exact chances that your unruptured brain aneurysm will rupture is one of the most common—and most stressful—concerns. The direct answer is that doctors cannot predict what a single aneurysm will do with absolute certainty. Instead, they estimate your personal risk by looking at specific features of your aneurysm, your overall health, and statistical scoring systems based on large groups of patients ^[1][2]. This estimate is then carefully weighed against your life expectancy, symptoms, and the risks of treating the aneurysm by a multidisciplinary team to help you make an informed choice ^[3].

Factors That Influence Rupture Risk

Your specialist will evaluate two main categories of information: the physical characteristics of the aneurysm itself and your personal medical history.

Features of the Aneurysm

• Size and Location: These are among the most reliable predictors of a rupture ^[1]. Generally, aneurysms larger than 7 millimeters have a higher risk, though there is no single “safe” size cutoff ^[4]. Aneurysms located in certain areas, such as the posterior communicating artery (a specific blood vessel at the base of the brain), also carry higher risks ^[2].
• Shape: Aneurysms that are irregular, have multiple lobes, or possess small blister-like bumps (often called “daughter sacs” or “blebs”) are considered higher risk than smooth, round aneurysms ^[5].
• Documented Growth: If follow-up imaging confirms that an untreated aneurysm has grown, this is a major warning sign requiring prompt specialist review ^[5]. While one study found that aneurysms growing by 1 millimeter or more had a group average risk of about 4.3% in the first year after growth, this is not a universal rule ^[5]. Post-growth risk varies based on the aneurysm’s baseline size and shape. Furthermore, a 1-millimeter difference between scans might sometimes just reflect differences in imaging equipment rather than true growth ^[6].
• Multiple Aneurysms: Having more than one aneurysm is sometimes considered in risk evaluations, though research is mixed on exactly how much this independently increases your risk ^[7].

Personal Health and History

• High Blood Pressure: Chronic, uncontrolled hypertension puts extra stress on the blood vessel walls and increases rupture risk ^[2][8]. Actively managing your blood pressure is one of the most important things you can do to lower your risk.
• Smoking: Current smoking is strongly linked to aneurysm growth and a higher chance of rupture ^[8][9]. Quitting smoking can actively improve your outlook.
• Family History: Having a first-degree relative (parent, sibling, or child) who has suffered a ruptured aneurysm (an aneurysmal subarachnoid hemorrhage) can increase your personal risk, and this risk generally increases if multiple relatives are affected ^[9].
• Prior Ruptures: If you have previously suffered a subarachnoid hemorrhage from a different aneurysm, any remaining unruptured aneurysms may have a higher risk of rupturing ^[2].
• Age: Older age affects rupture risk estimates, but it also heavily impacts the procedural risks and potential benefits of preventive treatment ^[3].

The PHASES Score: Estimating Your 5-Year Risk

To help standardize risk estimates, doctors often use a tool called the PHASES score. This system assigns points based on six specific factors ^[2]:

• Population: Studies found different baseline risks in specific populations (North American/European, Japanese, or Finnish).
• Hypertension: A history of high blood pressure.
• Age: Being 70 years or older.
• Size of the aneurysm.
• Earlier bleeding from another aneurysm.
• Site: Location of the aneurysm in the brain.

When your doctor totals your points, the score corresponds to a statistical group estimate of rupture risk over the next five years. For example, a low score of 0 to 2 corresponds to a 0.4% risk over five years (meaning about 4 out of 1,000 people with this score would experience a rupture in five years), while scores of 13 or higher estimate a 5-year risk of nearly 18% ^[10].

Limitations of Risk Scores

The PHASES score is a helpful starting point, but it is a group average, not a guarantee for your specific body ^[11]. Because the low-risk group is so large, a significant number of aneurysms that eventually rupture actually had “low-risk” PHASES scores before the event ^[10]. Furthermore, the PHASES score does not account for critical factors like aneurysm shape, growth over time, smoking status, or family history ^[9][5].

5-Year Risk vs. Lifetime Risk

• 5-Year Risk: Tools like the PHASES score focus on the short-term horizon (the next 5 years) ^[2].
• Lifetime Risk: This is the cumulative chance that the aneurysm will rupture during the remainder of your natural life. Estimating lifetime risk is complex because a person’s health, blood pressure, and aneurysm shape change over decades ^[7]. You cannot simply multiply a 5-year estimate to get your lifetime risk. However, life expectancy matters: a young person with a low 5-year risk might have a higher lifetime probability of rupture simply because they have many decades left to live, assuming the hazard remains present ^[3].

Weighing Rupture Risk Against Treatment Risk

Understanding your estimated rupture risk is only half the equation; the other half is understanding the risks of preventive treatment. Treatments are not universally interchangeable and depend heavily on the aneurysm’s anatomy and your overall health.

• Endovascular Treatments: These are minimally invasive procedures performed from inside the blood vessel, such as coiling (packing the aneurysm with wire coils) or flow diversion (placing a stent to divert blood away).
• Open Surgery (Clipping): A neurosurgeon places a tiny metal clip across the base of the aneurysm to seal it off.

Every procedure carries risks of complications, such as stroke, bleeding, or other new neurological deficits ^[12]. In a pooled analysis of recent studies, endovascular procedures carried roughly a 5% average risk of significant clinical complications within 30 days, while open neurosurgical treatments carried an approximately 8% risk ^[12]. However, endovascular treatments, particularly coiling, are more likely to require follow-up procedures (retreatment) later on compared to surgical clipping ^[13]. Keep in mind that these are broad averages; your personal procedural risk depends heavily on the specific size, shape, and location of your aneurysm, as well as the treating center’s expertise ^[14].

Because of these trade-offs, your care team will use shared decision-making ^[3]. There is no universal mathematical rule that dictates when to treat. Instead, a multidisciplinary team will compare your specific rupture risk over time against the localized procedural risks of treating your specific aneurysm, while incorporating your personal preferences and health goals ^[3].

If the balance favors treatment, it will be recommended; if the risks of treatment are deemed higher than the risks of living with the aneurysm, they will likely recommend ongoing monitoring (surveillance). Monitoring involves regular imaging (like MRA or CTA scans). The type of scan and how often it is performed are highly individualized based on your aneurysm’s features ^[7].