How Common Are Brain Aneurysms and What Causes Them?

It is natural to wonder why a brain aneurysm formed and whether it is a rare or common condition. In the general adult population, unruptured brain aneurysms are found in a minority of adults—an estimated 3.9% (or roughly 1 in 25 people) ^[1].

Because medical imaging has become more common, aneurysms are frequently discovered incidentally when a person gets a brain scan for an unrelated reason, such as a minor head injury or a headache ^[2][3]. It is important to know that an aneurysm found incidentally may not be the cause of the symptom that prompted the scan.

Understanding Rupture Risk

Finding an aneurysm can be frightening, but discovering one does not mean a life-threatening rupture is imminent. Many unruptured aneurysms remain stable and never burst throughout a person’s lifetime ^[4].

Worldwide, the incidence of ruptured aneurysms (which cause a bleeding stroke called aneurysmal subarachnoid hemorrhage) is only about 6 to 7 people per 100,000 each year in the general population ^[5][6]. However, it is crucial to understand that this population-wide statistic does not represent your personal risk. The chance that a known aneurysm will rupture varies widely from person to person and depends heavily on the aneurysm’s size, shape, and location, as well as your age, blood pressure, and smoking habits.

EMERGENCY WARNING: If an aneurysm does rupture, it is a medical emergency. Call 911 (or your local emergency number) immediately if you or someone else experiences a sudden, “worst-ever” headache, new weakness or numbness, trouble speaking or seeing, a seizure, loss of consciousness, repeated vomiting, or a stiff neck. Do not wait for a routine doctor’s appointment.

How and Why Do Aneurysms Form?

Aneurysms do not have a single, simple cause. Most patients cannot point to one specific event or behavior that caused their aneurysm. Instead, an aneurysm forms when the layers of the artery wall lose their natural elasticity and structural strength ^[7].

Current research suggests this weakening is driven by a combination of inherited susceptibility and biological stress:

• Blood Flow (Hemodynamics): The way blood travels and changes direction through the brain’s branching arteries may create friction against the vessel walls ^[8][9].
• Inflammation: Stressed blood vessels may trigger a local inflammatory response. Over time, immune cells (like macrophages) may break down the collagen and elastic fibers that give the artery wall its strength, allowing the wall to stretch and bulge out ^[10][11].

Risk Factors You Cannot Control

Certain demographic and genetic factors are associated with a higher likelihood of developing an aneurysm.

• Age and Sex: Brain aneurysms are rarely present at birth. They develop over time and are more common as people get older ^[12][13]. They are also roughly twice as common in women, particularly at older ages ^[1].
• Family History: Having two or more first-degree relatives (parents, siblings, or children) who have had a brain aneurysm or an aneurysmal subarachnoid hemorrhage increases your risk. In these cases, clinicians may discuss screening options for family members ^[14].
• Genetic Syndromes: Certain hereditary conditions significantly increase prevalence. For example, about 10% of people with Autosomal Dominant Polycystic Kidney Disease (ADPKD) have an aneurysm ^[15]. Certain specific genetic connective tissue disorders are also linked to a higher risk ^[1].

Modifiable Risk Factors (What You Can Control)

While you cannot change your genetics, two major risk factors contribute to both the formation and potential growth of aneurysms. These are areas where you and your doctor can take action:

1. Smoking: Cigarette smoking is one of the most consistent risk factors for aneurysm formation and growth ^[1][16]. Quitting smoking lowers your risk and is one of the most important steps you can take.
2. High Blood Pressure (Hypertension): Chronically high blood pressure places constant physical stress on the artery walls ^[1][16]. Keeping your blood pressure well-controlled with your doctor’s guidance helps protect your blood vessels.

Does Stress Cause Aneurysms?

A very common question is whether a demanding job, emotional distress, or a high-stress lifestyle caused the aneurysm. Chronic psychological stress is not an established direct cause of aneurysm formation. You should not blame yourself or your job for your diagnosis ^[17].

However, sudden, intense emotional arousal or extreme physical exertion can cause sharp spikes in blood pressure. While ordinary daily activities and normal stress are generally safe, you should ask your neurovascular specialist if there are specific unusually strenuous activities or heavy lifting you should avoid. Overall, managing stress is recommended because it helps improve sleep and maintain healthy, stable blood pressure ^[17].

What Happens Next?

If you have just discovered an incidental unruptured aneurysm, the next steps typically involve:

• Consulting a Specialist: You will likely be referred to a neurovascular specialist or neurosurgeon who will review your scans.
• Personalized Assessment: The specialist will look at the size, shape, and location of your aneurysm to estimate your specific risk.
• Making a Plan: Together, you will balance the risks of the aneurysm against the risks of any intervention. Many small, low-risk aneurysms are simply monitored with regular imaging, while others may be recommended for preventive treatment.
• Managing Health: In the meantime, work with your primary care doctor to control your blood pressure and stop smoking if you use nicotine products. Do not stop or change prescribed medications without medical advice.