What Is a Brain Aneurysm?

Brain aneurysms are classified by their shape, location, and underlying cause. Understanding the type helps determine the risk of rupture and the best treatment approach. Saccular aneurysms, also called berry aneurysms, are the most common type, accounting for about 90 percent of all brain aneurysms. They form a round, dome-shaped sac that bulges out from a weak spot in the artery wall, connected by a narrow neck. They most often occur at the base of the brain where major arteries branch off. Fusiform aneurysms are less common. Instead of forming a distinct sac, they cause a widened, bulging section of the artery that affects all sides of the vessel. They do not have a defined neck. Mycotic aneurysms are rare and are caused by a bacterial infection that weakens the artery wall. The infection typically spreads from another part of the body, such as a heart valve infection. Aneurysms are also classified by size:

• Small aneurysms: less than 11 millimeters (about the size of a pencil eraser)
• Large aneurysms: 11 to 25 millimeters (about the size of a dime)
• Giant aneurysms: larger than 25 millimeters (wider than a quarter)

Size is an important factor in determining the risk of rupture. Larger aneurysms are generally more likely to rupture than smaller ones.

The symptoms of a brain aneurysm depend entirely on whether it has ruptured or not. Most unruptured aneurysms cause no symptoms at all and are discovered incidentally during imaging tests performed for unrelated health concerns such as headaches or injuries. When an unruptured aneurysm grows large enough to press on surrounding nerves or brain tissue, it can cause:

• A persistent headache or pain behind or above the eye
• Blurred or double vision
• A drooping eyelid
• A dilated pupil
• Numbness or weakness on one side of the face
• Difficulty speaking

A leaking aneurysm may cause a sudden, severe headache known as a sentinel headache. This can occur days or weeks before a full rupture and serves as a critical warning sign that should never be ignored. A ruptured aneurysm is a medical emergency. Symptoms include:

• A sudden, extremely severe headache often described as the worst headache of your life (thunderclap headache)
• Stiff neck
• Nausea and vomiting
• Sensitivity to light
• Blurred or double vision
• Drooping eyelid
• Confusion or difficulty with mental awareness
• Seizures
• Loss of consciousness
• Cardiac arrest in severe cases

If you or someone near you experiences a sudden, severe headache or any of these symptoms, call 911 immediately. Prompt treatment is critical for survival.

A brain aneurysm forms when a section of an artery wall in the brain becomes weak and bulges outward. The exact reason this happens is not always clear, but several factors contribute to the weakening of the artery wall. Aneurysms tend to form where arteries branch into smaller vessels. These branching points are naturally weaker, and the constant pressure of blood flow can cause a weakened area to balloon out over time. Several factors increase the risk of developing a brain aneurysm:

• High blood pressure is the most significant risk factor. Untreated hypertension places constant stress on artery walls, making them more likely to weaken and bulge.
• Smoking damages the lining of blood vessels and accelerates the development of aneurysms.
• Age is a factor — aneurysms become more common after age 40.
• Women have a higher risk than men.
• A family history of brain aneurysms increases your risk.
• Certain genetic conditions are strongly linked to aneurysms, including autosomal dominant polycystic kidney disease (ADPKD), Ehlers-Danlos syndrome, Marfan syndrome, and neurofibromatosis type 1.
• Atherosclerosis, a buildup of fatty plaque in the arteries, can contribute to vessel wall weakness.
• Head trauma can sometimes damage an artery and lead to aneurysm formation.
• Infections can cause mycotic aneurysms, though these are rare.

Several factors can trigger a rupture in an existing aneurysm:

• A sudden spike in blood pressure from heavy lifting, intense exercise, or strong emotions
• Straining during bowel movements
• The use of stimulant drugs such as cocaine or amphetamines
• The use of blood thinners

Not everyone with these risk factors will develop an aneurysm, and some people with no known risk factors still develop them.

Brain aneurysms are often discovered incidentally when a person undergoes brain imaging for an unrelated reason, such as a head injury or persistent headaches. When a rupture is suspected, diagnosis is urgent. Several imaging tests can detect and evaluate brain aneurysms: CT scan (computed tomography) is often the first test used when a rupture is suspected. It can quickly detect bleeding in the brain. A CT angiogram uses a contrast dye injected into a vein to create detailed images of the blood vessels. MRI (magnetic resonance imaging) and MRA (magnetic resonance angiography) use magnetic fields and radio waves to produce detailed images of the brain and its blood vessels. These are particularly useful for detecting unruptured aneurysms. Digital subtraction angiography (DSA) is considered the gold standard for detecting and evaluating brain aneurysms. A thin, flexible catheter is inserted into an artery in the groin or wrist and threaded up to the blood vessels in the neck and brain. A contrast dye is injected, and X-rays are taken to create a detailed map of the brain’s blood flow. This test can pinpoint the exact location, size, and shape of an aneurysm. Lumbar puncture (spinal tap) may be used if a CT scan does not show bleeding but a ruptured aneurysm is still suspected. A needle is inserted into the lower back to collect cerebrospinal fluid, which is tested for the presence of blood. The choice of test depends on the situation. In an emergency, a CT scan is typically done first. For monitoring known aneurysms, MRI or MRA is often preferred because it does not involve radiation.

There is no guaranteed way to prevent a brain aneurysm from forming, but there are effective strategies to reduce your risk and to prevent an existing aneurysm from rupturing. Control your blood pressure. High blood pressure is the single most important risk factor for both the development and rupture of brain aneurysms. Have your blood pressure checked regularly, and if it is elevated, work with your doctor to manage it through lifestyle changes and medication if needed. Do not smoke. Smoking damages blood vessel walls and significantly increases the risk of aneurysm formation and rupture. Quitting smoking lowers your risk over time. Avoid stimulant drugs. Cocaine, amphetamines, and other stimulants can cause sudden spikes in blood pressure that can trigger a rupture. Limit alcohol. Heavy drinking and binge drinking can raise blood pressure and increase the risk of rupture. If you drink, do so in moderation. Avoid heavy lifting and straining. Activities that cause a sudden increase in pressure inside the head can trigger a rupture in a vulnerable aneurysm. Use proper lifting techniques and avoid extreme exertion. Manage stress. Intense emotions such as anger or extreme stress can cause blood pressure spikes. Finding healthy ways to manage stress is important. Eat a heart-healthy diet and maintain a healthy weight. These habits help control blood pressure and reduce the overall strain on your blood vessels. If you have a known family history of brain aneurysms, talk to your doctor about whether screening is appropriate. Early detection of an unruptured aneurysm allows for monitoring or preventive treatment before a rupture occurs.

The outlook for a brain aneurysm depends heavily on whether it ruptures. The majority of brain aneurysms never rupture. Estimates suggest that 50 to 80 percent of all brain aneurysms remain stable and never cause problems throughout a person’s lifetime. For unruptured aneurysms, the outlook is generally excellent. Many people live their entire lives without ever knowing they have one. Small aneurysms with no risk factors can be safely monitored with regular imaging, and if treatment is needed, elective procedures have high success rates. For ruptured aneurysms, the outlook is more serious. About 30,000 people in the United States experience a ruptured brain aneurysm each year. Approximately 50 percent of those individuals die within the first three months. Of those who survive, about 66 percent have some degree of permanent brain damage. About 75 percent of people with a ruptured aneurysm survive the first 24 hours. However, complications can develop in the following days and weeks, including re-bleeding, vasospasm (narrowing of blood vessels that reduces blood flow to the brain), hydrocephalus (fluid buildup in the brain), and seizures. Recovery after a rupture can take weeks to months and often requires intensive rehabilitation, including physical therapy, occupational therapy, and speech therapy. The extent of recovery depends on the severity of the initial bleed, how quickly treatment was received, and the person’s overall health. Prompt emergency care and advances in treatment have improved outcomes for ruptured aneurysms over time. The key is seeking immediate medical attention at the first sign of symptoms.

Treatment for a brain aneurysm depends on its size, location, whether it has ruptured, and the person’s overall health. Options range from careful monitoring to surgical intervention. Small, unruptured aneurysms that are not causing symptoms and have a low risk of rupture may not require immediate treatment. Instead, the doctor may recommend regular imaging (every 6 to 12 months) to monitor for any changes in size or shape. Managing blood pressure and other risk factors is an essential part of this approach. Surgical clipping is an open brain surgery used to treat aneurysms that are at high risk of rupture or have already ruptured. A section of the skull is removed to access the aneurysm. A tiny metal clip is placed across the neck of the aneurysm, sealing it off from the artery and stopping blood flow into it. The clip remains in place permanently. This procedure is highly effective but requires a longer recovery time. Endovascular coiling is a less invasive alternative. A catheter is inserted into an artery in the groin or wrist and threaded through the blood vessels up to the aneurysm. Tiny platinum coils are released into the aneurysm, filling it and causing blood to clot inside, which blocks blood flow. This procedure has a shorter recovery time than clipping but carries a slightly higher risk of the aneurysm bleeding again over time. Flow diverters are stent-like devices used for larger or more complex aneurysms that cannot be treated with clipping or coiling. A catheter is used to place the flow diverter in the parent artery, where it redirects blood flow away from the aneurysm. Over time, the aneurysm shrinks and may eventually close off completely. After a rupture, additional treatments may be needed:

• Calcium channel blockers to prevent vasospasm
• Antiseizure medications
• A ventricular drain to reduce pressure from fluid buildup in the brain
• Shunt surgery to permanently drain excess fluid
• Physical, occupational, and speech therapy for rehabilitation

The choice of treatment is made by a team of specialists, including neurosurgeons and interventional radiologists, based on the individual’s specific situation.

Diet plays an important role in managing brain aneurysm risk, primarily by helping to control blood pressure and supporting overall vascular health. A heart-healthy diet is the most recommended approach. This means emphasizing fruits, vegetables, whole grains, lean proteins, and healthy fats while limiting sodium, saturated fats, and added sugars. Reducing sodium is one of the most important dietary steps for controlling blood pressure. Aim for less than 2,300 milligrams of sodium per day — and ideally less if you have high blood pressure. This means limiting processed foods, canned soups, salty snacks, and restaurant meals, and cooking with herbs and spices instead of salt. Potassium-rich foods can help counteract the effects of sodium on blood pressure. Good sources include bananas, potatoes, spinach, avocados, sweet potatoes, and beans. Fiber is important for preventing constipation and straining during bowel movements, which can cause a dangerous spike in blood pressure. High-fiber foods include oats, beans, lentils, fruits, vegetables, and whole grains. Omega-3 fatty acids from fatty fish such as salmon, mackerel, and sardines, as well as flaxseeds and walnuts, have anti-inflammatory properties that support blood vessel health. What to limit:

• Caffeine can cause a temporary increase in blood pressure. If you have high blood pressure or a known aneurysm, consider reducing your caffeine intake.
• Alcohol, especially in large amounts, raises blood pressure and can increase the risk of rupture.
• Heavy meals can sometimes cause a temporary increase in blood pressure.

Staying well hydrated supports healthy blood volume and circulation. Maintaining a healthy weight through diet is important because excess weight contributes to high blood pressure and puts additional strain on the cardiovascular system.

A brain aneurysm is a weakened, bulging area in the wall of an artery in the brain that can be thought of as a balloon-like outpouching. Most brain aneurysms are small and never rupture, often going unnoticed and causing no health problems throughout a person’s life. However, when an aneurysm ruptures, it causes bleeding around the brain — a subarachnoid hemorrhage — that is life-threatening and requires immediate emergency treatment. The most common symptom of a rupture is a sudden, severe headache often described as the worst headache of your life. Other symptoms include stiff neck, nausea, sensitivity to light, seizure, and loss of consciousness. The primary risk factors for developing an aneurysm are high blood pressure, smoking, age over 40, female sex, family history, and certain genetic conditions. Diagnosis is typically made through imaging such as CT angiography, MRI/MRA, or digital subtraction angiography. For small, unruptured aneurysms, careful monitoring and blood pressure management may be sufficient. For larger or ruptured aneurysms, treatment options include surgical clipping, endovascular coiling, or flow diverter placement. With proper management, the vast majority of unruptured aneurysms remain stable, and even after a rupture, prompt medical treatment significantly improves the chances of survival and recovery.