A brain aneurysm is a bulge in a blood vessel inside your skull

A brain aneurysm is a weak spot in an artery inside your brain where the vessel wall balloons outward. The bulge fills with blood and can grow larger over time. Most people with an unruptured aneurysm have no symptoms and never know it exists. The real danger comes if the aneurysm ruptures — the vessel breaks open and blood spills into the space around your brain, which is a medical emergency.

The location and size of an aneurysm determine the risk. A small aneurysm in a less critical area may never cause problems. A large one or one in a vulnerable spot can rupture with little warning. Rupture happens suddenly and without a preceding event — you cannot predict it by how you feel.

Key Takeaways

  • An unruptured brain aneurysm is a bulge in a blood vessel that usually causes no symptoms and is often found by accident during imaging for another reason.
  • Rupture causes sudden severe headache, neck stiffness, vision changes, and loss of consciousness, and requires emergency care within hours.
  • Risk factors include high blood pressure, smoking, family history of aneurysm, and certain genetic conditions like polycystic kidney disease.
  • Doctors decide whether to treat an unruptured aneurysm based on its size, location, and your age and health history, not on symptoms alone.
  • Treatment options are surgical clipping or endovascular coiling, both performed by neurosurgeons or interventional radiologists in a hospital setting.

Where aneurysms form and why they develop

Brain aneurysms most often form where arteries branch, because those junctions experience more stress from blood flow. The most common location is the circle of Willis, a ring of arteries at the base of the brain. Aneurysms can also form in the middle cerebral artery or the vertebral artery, depending on the person.

The exact cause of aneurysm formation is not fully understood, but certain conditions weaken artery walls. High blood pressure puts constant strain on vessels. Smoking damages the inner lining of arteries. Atherosclerosis — buildup of plaque in vessel walls — can contribute. Some people are born with connective tissue disorders like Ehlers-Danlos syndrome or polycystic kidney disease that make aneurysm more likely. Family history matters: if a parent or sibling had an aneurysm, your risk is higher.

The difference between unruptured and ruptured aneurysms

An unruptured aneurysm is one that has not broken. You typically have no warning signs. Many are found by accident when you get an MRI or CT scan for a different reason — a headache, a fall, or imaging done for another condition. Once found, doctors monitor it with follow-up imaging every few months or years, depending on size and risk factors.

A ruptured aneurysm is a medical emergency. Symptoms come on suddenly and severely: the worst headache of your life, often described as being hit with a hammer; stiff neck; sensitivity to light; nausea and vomiting; vision changes; loss of consciousness; or seizure. Some people lose consciousness immediately. Others remain awake but confused. If you or someone near you experiences these symptoms, call 911 immediately. Survival depends on reaching a hospital within hours.

How doctors find and measure an aneurysm

An unruptured aneurysm is usually found during imaging ordered for another reason. The imaging types that show aneurysms are CT scan, MRI, or CT angiography (CTA), which uses contrast dye to highlight blood vessels. Once found, the doctor measures the aneurysm in millimeters and notes its exact location and shape.

If you have had a ruptured aneurysm, diagnosis is faster and more urgent. A CT scan of the head is done immediately in the emergency room. If the CT shows blood in the space around the brain (subarachnoid hemorrhage), a lumbar puncture (spinal tap) may be done to confirm. Once rupture is confirmed, a cerebral angiogram — an X-ray taken while contrast dye flows through brain arteries — pinpoints the exact aneurysm so treatment can begin.

Treatment decisions for unruptured aneurysms

Not every unruptured aneurysm needs treatment. Doctors weigh the risk that it will rupture against the risk of treating it. A small aneurysm (less than 5 millimeters) in a low-risk location in a younger person may be monitored with imaging every year or two. A larger aneurysm, one in a high-risk location, or one in a person with a family history of rupture is more likely to be treated.

Your age, overall health, and ability to tolerate surgery or a procedure also factor in. A 40-year-old with good health and a 7-millimeter aneurysm might be offered treatment. A 75-year-old with heart disease and the same aneurysm might be monitored instead. The decision is made together with your neurologist or neurosurgeon, not based on a single rule.

Surgical and non-surgical treatment options

The two main ways to treat an aneurysm are surgical clipping and endovascular coiling. Both are performed in a hospital by a neurosurgeon or interventional radiologist.

In surgical clipping, a neurosurgeon opens the skull, locates the aneurysm, and places a small metal clip across the neck of the bulge to stop blood from flowing into it. The clip stays in place permanently. This is open brain surgery and requires general anesthesia and a hospital stay of several days. Recovery takes weeks to months.

In endovascular coiling, an interventional radiologist threads a thin catheter through an artery in your groin up to the aneurysm. Tiny coils of platinum wire are pushed through the catheter into the aneurysm to fill it and block blood flow. This is less invasive than surgery — no incision in the skull — but may require a longer hospital stay and follow-up imaging. Some aneurysms need both coiling and a stent (a small mesh tube) to hold the coils in place.

Your doctor recommends one approach based on the aneurysm's size, shape, location, and your age and health. Neither option is risk-free, but both reduce the chance of rupture significantly.

Living with an unruptured aneurysm

If you have an unruptured aneurysm that is being monitored, you can live a normal life. You do not need to avoid exercise, sex, or normal activities. You should manage high blood pressure with medication if you have it, and stop smoking if you do. These steps reduce the risk that the aneurysm will grow or rupture.

Keep your follow-up imaging appointments. The schedule depends on the size and location of your aneurysm — your doctor will tell you when to return. If you develop sudden severe headache, neck stiffness, vision changes, or loss of consciousness, seek emergency care immediately, even if you have had an aneurysm for years without problems. These symptoms can signal rupture or a new problem.

Tell your family members about your aneurysm. If you have a first-degree relative (parent, sibling, or child) with an aneurysm, they may benefit from screening with imaging, especially if they have high blood pressure or smoke.

Frequently Asked Questions

Can a small aneurysm rupture without warning?

Yes. Size does not predict rupture. Most ruptured aneurysms are small to medium-sized. A very large aneurysm may never rupture. This is why doctors consider location, shape, and your risk factors, not size alone, when deciding whether to treat.

What should I do if I have a severe headache and I know I have an aneurysm?

Call 911 or go to the emergency room immediately. Do not wait to see if it passes. A sudden severe headache in someone with a known aneurysm must be evaluated right away, even if it turns out to be a migraine or tension headache.

Does having high blood pressure mean I will get an aneurysm?

No. High blood pressure increases the risk, but most people with high blood pressure never develop an aneurysm. Controlling your blood pressure with medication and lifestyle changes reduces the risk of both aneurysm formation and rupture.

Can an aneurysm come back after treatment?

After surgical clipping, recurrence is rare. After coiling, a small percentage of aneurysms can regrow or recanalize (blood can flow into it again), which is why follow-up imaging is sometimes recommended. Your doctor will tell you if you need long-term monitoring.

Is it safe to fly or travel if I have an unruptured aneurysm?

Yes. Flying and travel do not increase the risk of rupture. You can travel normally. If you are traveling far from home, it may be helpful to know where the nearest major hospital is, but this is a precaution, not a requirement.