A cerebral aneurysm is a weak spot in an artery inside your brain that balloons outward

The arteries in your brain carry blood under pressure, just like pipes in a house carry water. A cerebral aneurysm forms when the wall of one of these arteries thins and weakens, causing a bulge or pouch to form. The bulge itself usually causes no symptoms—most people with an aneurysm never know they have one. The danger comes if the bulge ruptures and bleeds into the space around your brain, which is a medical emergency.

Think of it like a weak spot in a tire: the tire may hold air for years, or the weak spot may suddenly give way. With aneurysms, doctors cannot predict which ones will rupture and which will remain stable. This uncertainty shapes how aneurysms are found, monitored, and treated.

Key Takeaways

  • Most cerebral aneurysms cause no symptoms and are found by accident during imaging for other reasons.
  • A ruptured aneurysm causes sudden severe headache, neck stiffness, and loss of consciousness—call 911 immediately if these occur.
  • Doctors use CT scans and angiography to find aneurysms and decide whether to treat them or monitor them over time.
  • Treatment options include surgery to clip the aneurysm or a catheter procedure to fill it with coils, each with different recovery times and risks.
  • Risk factors include high blood pressure, smoking, family history, and certain genetic conditions, though aneurysms can occur in people with none of these.

How an aneurysm forms and why it matters

The wall of an artery has three layers: a tough outer layer, a muscular middle layer, and a smooth inner lining. An aneurysm forms when the middle muscular layer weakens. Over time, blood pressure pushes against this weak spot, and the inner lining bulges outward like a balloon. The bulge grows slowly or stays the same size for years.

The risk is rupture. When an aneurysm ruptures, blood spills into the subarachnoid space—the area between the brain and the membrane that covers it. This bleeding is called a subarachnoid hemorrhage. The sudden pressure and blood irritate the brain tissue, and the bleeding can damage brain cells. A ruptured aneurysm is life-threatening: about one in three people who have one die, and many survivors have lasting brain damage.

Not all aneurysms rupture. Small aneurysms that are not growing may never cause a problem. Larger ones or ones in certain locations carry higher rupture risk. This is why finding an aneurysm raises a difficult question: treat it now and accept the risks of surgery, or watch it and accept the risk that it might rupture.

Symptoms of a ruptured aneurysm versus an unruptured one

An unruptured aneurysm almost never causes symptoms. You could have one and feel completely normal. Some people have a large aneurysm that presses on nearby brain tissue and causes headaches, vision problems, or facial pain, but this is uncommon. Most unruptured aneurysms are found by accident—during an MRI or CT scan done for a different reason, like a head injury or stroke screening.

A ruptured aneurysm announces itself suddenly. The classic sign is the worst headache of your life—people often describe it as being hit in the back of the head with a hammer. Other signs appear within minutes: stiff neck, sensitivity to light, nausea and vomiting, loss of consciousness, or seizure. Some people have a smaller leak first (called a sentinel bleed) with a sudden bad headache but no loss of consciousness. If you experience any of these symptoms, call 911. The first hours after rupture are critical for survival and recovery.

How doctors find and diagnose an aneurysm

When a ruptured aneurysm is suspected, a CT scan of the head is done first. It shows blood in the brain and around it. If the CT is positive, a cerebral angiogram follows—a catheter is threaded through an artery in the groin up to the brain, and dye is injected so the aneurysm shows clearly on X-ray. This test pinpoints the exact location and shape of the aneurysm and guides treatment decisions.

For an unruptured aneurysm found by accident, doctors use CT angiography or MR angiography to get detailed images without inserting a catheter. These tests show the size, shape, and location of the aneurysm. Doctors then assess rupture risk based on the aneurysm's size, location, shape, and whether it is growing. An aneurysm larger than 7 millimeters, located in certain high-risk spots, or with an irregular shape carries higher rupture risk.

If an unruptured aneurysm is found, follow-up imaging is often recommended. Small, stable aneurysms may be rescanned every 6 to 12 months for the first year or two, then less often if they are not growing. Larger aneurysms or those in high-risk locations may be treated sooner rather than watched.

Treatment options: surgery versus catheter procedures

Two main treatments exist for aneurysms: surgical clipping and endovascular coiling. The choice depends on the aneurysm's size, shape, location, and the person's age and overall health.

Surgical clipping is open brain surgery. A neurosurgeon makes an incision in the scalp, opens the skull, and places a small metal clip across the neck of the aneurysm to stop blood from flowing into it. The clip stays in place permanently. Recovery takes weeks to months. Risks include infection, bleeding, stroke, and brain swelling. The advantage is that clipping is permanent and works well for many aneurysm shapes.

Endovascular coiling is less invasive. A catheter is threaded through an artery to the aneurysm, and soft platinum coils are pushed through the catheter into the aneurysm sac. The coils cause blood to clot inside the aneurysm, sealing it off. Recovery is faster than surgery—often just a day or two in the hospital. Risks include stroke, perforation of the aneurysm, and coil migration. A disadvantage is that coils can shift over time, so some aneurysms need retreatment years later.

For a ruptured aneurysm, treatment is urgent—usually within 24 to 48 hours of the bleed. For an unruptured aneurysm, the timing is less pressing, and the decision to treat at all depends on rupture risk versus surgical risk.

Risk factors that make aneurysms more likely

Certain conditions and habits increase the chance of developing an aneurysm. High blood pressure is the strongest modifiable risk factor—it stresses artery walls over time. Smoking damages artery walls and is linked to both aneurysm formation and rupture. Family history matters: if a parent or sibling had an aneurysm, your risk is higher. Age also plays a role—aneurysms are more common in people over 40, though they can occur at any age.

Certain genetic conditions carry high aneurysm risk. Polycystic kidney disease, Ehlers-Danlos syndrome, and Marfan syndrome all weaken connective tissue and increase aneurysm risk. People with these conditions are sometimes screened for aneurysms even if they have no symptoms.

Other factors include heavy alcohol use, cocaine use, and connective tissue disorders. Having one or more risk factors does not mean you will develop an aneurysm—many people with risk factors never do. Conversely, aneurysms occur in people with no known risk factors.

Living with an unruptured aneurysm

If you are told you have an unruptured aneurysm, the first step is understanding your specific situation. Ask your doctor about the aneurysm's size, location, and estimated rupture risk. Ask whether monitoring or treatment is recommended and why. Get a second opinion if you are unsure—the decision between watching and treating is not always straightforward, and different specialists may weigh the risks differently.

If monitoring is chosen, keep follow-up appointments for imaging. Bring a list of questions each time. Report any new symptoms—sudden headaches, vision changes, or neck pain—to your doctor right away, even between scheduled visits. Control modifiable risk factors: manage blood pressure, stop smoking, limit alcohol, and avoid cocaine and stimulants.

Many people live for years or decades with a stable unruptured aneurysm and never have problems. Others choose treatment for peace of mind, even if rupture risk is low. Both approaches are reasonable depending on your values and circumstances.

Frequently Asked Questions

Can stress or exercise cause an aneurysm to rupture?

Sudden stress or strenuous exercise can temporarily raise blood pressure and may trigger rupture in an aneurysm that is already at high risk. However, normal daily activities do not cause rupture in stable aneurysms. If you have an unruptured aneurysm, ask your doctor what level of activity is safe for you.

If I have an aneurysm, will I definitely have a stroke?

No. An unruptured aneurysm does not cause stroke unless it ruptures. A ruptured aneurysm can cause stroke as a complication, but not everyone who has a rupture has a stroke. The outcomes vary widely depending on the size of the bleed and how quickly treatment is given.

Can an aneurysm heal on its own?

An aneurysm does not heal or shrink on its own. Once formed, it stays the same size or grows slowly over time. Treatment—either surgery or coiling—is the only way to seal it off. Monitoring is not a cure; it is a way to catch growth or rupture early.

What should I do if I have a family history of aneurysms?

Talk to your doctor about your family history. If multiple relatives had aneurysms or if you have a genetic condition linked to aneurysms, screening with CT or MR angiography may be recommended. If screening finds an aneurysm, your doctor will discuss monitoring or treatment options based on its characteristics.