Brain Aneurysm: Symptoms, Causes, and Treatment
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick answer
A brain aneurysm is a ballooning in a weakened area of a blood vessel in the brain, often shaped like a berry on a stem. It usually causes no symptoms, but a rupture causes a sudden, extremely severe headache with nausea, stiff neck or loss of consciousness. Ruptured aneurysms are repaired with clipping or endovascular coiling. [1] [2]
What the research says
According to PubMed:
Unruptured aneurysms are more common in some groups. A meta-analysis of 316,131 participants estimated unruptured aneurysm prevalence at 3.9% in a reference population (mean age 50, 50% women); risk ratios were 1.9 for female sex, 1.4 for current smoking, and 1.6 for hypertension, and prevalence was higher with connective-tissue disorders (adjusted prevalence ratio 3.9) and polycystic kidney disease (4.4) (Dremel et al., DOI).
Treatment choice involves trade-offs. A meta-analysis of 17 observational studies (2,289 patients) found the Woven EndoBridge device had lower rates of adequate occlusion than microsurgical clipping (RR 0.77), similar complete occlusion to stent-assisted coiling, and fewer procedure-related complications than stent-assisted coiling (RR 0.49) (Ahmed et al., DOI).
Preventing clots during endovascular repair. In a phase 2 randomized trial of 191 patients, adding tirofiban to dual antiplatelet therapy reduced the median volume of new infarcts after endovascular repair of unruptured aneurysms (48.6 vs 88.2 mm³) without significant differences in symptomatic stroke or hemorrhage; the authors call for validation in a larger trial (Hu et al., DOI).
Study details are from PubMed abstracts.
What is a brain aneurysm?
An aneurysm is a ballooning at a weak spot in an artery wall. In a blood vessel of the brain it is called a brain aneurysm, cerebral aneurysm, or intracranial aneurysm [1].
Experts believe these bulges form and grow because blood flowing through the vessel presses against a weak area of the wall. If the wall leaks or tears open, blood escapes into the brain area, causing a hemorrhagic stroke. Most often a ruptured aneurysm bleeds into the space between the brain and the thin tissues covering it — a subarachnoid hemorrhage [1].
About 3 percent of adults have an unruptured brain aneurysm. Most are small, serious problems are uncommon, and most never rupture; many are found by chance during imaging for other conditions. If one does rupture, it quickly becomes life-threatening and requires emergency treatment [1].
The three main types
Saccular (berry) aneurysm: a round, blood-filled sac hanging from the main artery on a narrow stem, usually on arteries at the base of the brain; the most common type [1]
Fusiform aneurysm: the artery bulges outward on all sides rather than forming a single sac [1]
Mycotic aneurysm: caused by an infection of the brain's arteries that weakens the artery wall [1]
What are the symptoms of a brain aneurysm?
Most unruptured aneurysms cause no symptoms, especially when small. If one ruptures, the condition is very serious and typically causes a severe headache. An unruptured aneurysm that presses on brain tissue or nerves may cause pain and other symptoms [1].
Symptoms of a ruptured aneurysm
A sudden, severe headache is the key symptom — people often describe it as the worst headache they have ever had [1].
Symptom | What it looks like |
Nausea and vomiting | Feeling sick to the stomach, often with vomiting |
Stiff neck | The neck becomes hard and difficult to move |
Blurred or double vision | Trouble seeing clearly or seeing two images |
Sensitivity to light | Bright light feels painful or overwhelming |
Seizure | A sudden episode of uncontrolled electrical activity in the brain |
Loss of consciousness | Passing out or becoming unresponsive |
Confusion | Trouble thinking clearly or knowing where you are |
Symptoms of a leaking aneurysm
Sometimes an aneurysm leaks a small amount of blood before rupturing fully, and a more severe rupture often follows, sometimes days or weeks later. A leak may cause a sudden, extremely severe headache that lasts several days and up to two weeks [1].
Symptoms of an unruptured aneurysm
A larger unruptured aneurysm can press on brain tissues and nerves. Possible symptoms include pain above and behind one eye, a dilated pupil, a change in vision or double vision, numbness on one side of the face, and seizures [1].
When to seek emergency care: Get medical attention right away for any sudden, extremely severe headache. If you are with someone who develops a sudden, severe headache, loses consciousness, or has a seizure, call 911 or your local emergency number immediately [1].
What causes a brain aneurysm?
Brain aneurysms are caused by thinning artery walls. They often form at forks or branches in arteries because those areas are weaker. Although they can develop anywhere in the brain, they are most common in arteries at the base of the brain [1].
What are the risk factors?
Several factors weaken artery walls over time or are present from birth, and can raise the risk of developing an aneurysm or of an existing one rupturing [1].
Risk factor | Why it matters |
Age | Aneurysms can happen at any age but are most common in adults ages 30 to 60 |
Being female | Brain aneurysms are more common in women than in men |
Cigarette smoking | Smoking raises the risk of both forming an aneurysm and rupturing one |
High blood pressure | High pressure weakens arteries, making them more likely to form and rupture |
Drug use, especially cocaine | Drugs raise blood pressure, and injecting drugs can cause infections that weaken arteries |
Heavy alcohol use | Excess alcohol can increase blood pressure |
Inherited connective tissue conditions | Conditions such as Ehlers-Danlos syndrome weaken blood vessels |
Polycystic kidney disease | This inherited condition produces fluid-filled kidney sacs and may raise blood pressure |
Narrow aorta (coarctation) | A narrowed main artery from birth increases risk |
Brain arteriovenous malformation (AVM) | Tangled brain arteries and veins disrupt blood flow |
Family history | Risk is higher with family members who have had a brain aneurysm, especially two or more first-degree relatives |
Some aneurysms also develop after a head injury or from certain blood infections. An aneurysm is more likely to rupture when it is large, sits in certain locations, has an irregular shape, or has an outpouching called a daughter sac; smoking and untreated high blood pressure also raise rupture risk [1].
What complications can follow a rupture?
When a brain aneurysm ruptures, the bleeding usually lasts only a few seconds. Even so, the blood can damage surrounding cells, kill brain cells, and raise pressure inside the skull. If pressure climbs too high, it may cut off blood and oxygen to the brain, causing loss of consciousness or death [1].
Complication | What happens |
Re-bleeding | An aneurysm that ruptured or leaked can bleed again, causing further brain cell damage |
Vasospasm | Brain blood vessels contract and narrow after rupture, which can cause an ischemic stroke |
Hydrocephalus | Blood blocks the flow of cerebrospinal fluid, fluid builds up, and pressure damages brain tissue |
Change in sodium level | Bleeding disrupts blood sodium; a drop causes brain cell swelling and can lead to permanent damage |
How is a brain aneurysm diagnosed?
Tests start with the least invasive options and move to more detailed imaging when needed [2].
Test | How it works | What it finds |
CT scan | A specialized X-ray producing 2D slices of the brain; usually the first test | Signs of bleeding in the brain |
CT angiogram | Dye is injected into a vein to make blood flow easier to observe | Detailed artery images and the presence of an aneurysm |
Lumbar puncture (spinal tap) | A needle draws cerebrospinal fluid from the back | Red blood cells that indicate a subarachnoid hemorrhage when a CT scan is negative |
MRI | Magnetic field and radio waves create detailed brain images | Whether bleeding is present in the brain |
MR angiography | A type of MRI focused on arteries | The size, shape, and location of an aneurysm |
Cerebral angiogram | A thin catheter is threaded from an artery in the groin or wrist to brain arteries, dye is injected, and X-rays are taken | Detailed artery conditions when other tests give insufficient information |
Who should be screened?
Screening for unruptured aneurysms is usually reserved for people at high risk. Talk to a healthcare professional about screening if you have a family history of brain aneurysms or hemorrhagic stroke (particularly two first-degree relatives), or a condition that raises risk, such as polycystic kidney disease, coarctation of the aorta, or Ehlers-Danlos syndrome [2].
How is a brain aneurysm treated?
Repairing a ruptured aneurysm requires surgery or endovascular treatment (treating the aneurysm from inside the artery). The healthcare team weighs the aneurysm's size, location, and appearance; the patient's age and general health; family history of ruptured aneurysm; and conditions present from birth that raise rupture risk [2].
Surgical clipping
The neurosurgeon removes a section of the skull, locates the blood vessel that feeds the aneurysm, and places a tiny metal clip on the aneurysm's neck to stop blood flow into it. Clipping is very effective and clipped aneurysms typically do not return. Risks are low and include bleeding in the brain or loss of blood flow to the brain. Recovery usually takes about 4 to 6 weeks; people treated for an unruptured aneurysm may leave the hospital within a day or two, while recovery from a ruptured aneurysm takes much longer [2].
Endovascular coiling and stents
Endovascular treatment is less invasive than clipping and may be safer. A neurosurgeon threads a catheter through an artery, usually in the groin or wrist, to the aneurysm. During coiling, a tiny spiral-shaped wire coil placed inside the aneurysm prevents blood from flowing in and causes the blood already inside to clot. A stent may be used alongside a coil for some aneurysm types to hold it in place. The aneurysm can reappear over time, so follow-up imaging is important [2].
Flow diversion
Flow diversion places a stent (a flow diverter) inside the blood vessel to redirect blood flow away from the aneurysm. With less blood reaching it, rupture risk falls, and the stent prompts the body to grow new cells that seal the aneurysm closed. It can be especially useful for larger aneurysms that cannot be treated with other options, and for locations that are hard to reach [2].
Other procedures and medicines after a rupture
Angioplasty expands a narrowed brain blood vessel caused by vasospasm and can help prevent a stroke. Draining catheters and shunt surgery reduce pressure on the brain from a buildup of cerebrospinal fluid [2].
Medicine type | What it does |
Pain relievers | Medicines such as acetaminophen treat headache pain |
Calcium channel blockers | Lessen vasospasm symptoms; nimodipine reduces the risk of delayed brain injury after a subarachnoid hemorrhage |
Vessel-opening medicines (vasodilators) | Given through an IV or catheter to dilate brain blood vessels and help prevent stroke |
Anti-seizure medicines | Used to treat seizures related to a ruptured aneurysm, typically only if a seizure has occurred |
Damage from a subarachnoid hemorrhage may require physical, speech, and occupational therapy to relearn skills [2].
Treating unruptured aneurysms
A clip, coil, or flow diverter can seal off an unruptured aneurysm to prevent a future rupture. But rupture risk may be extremely low in some, and the known risks of the procedures may outweigh the benefits. A neurologist working with a neurosurgeon or interventional neuroradiologist can help decide whether treatment is right for you [2].
Prognosis after a rupture
Outcome depends on the person's age and health, other conditions, the size and location of the aneurysm, the amount of bleeding, and how much time passed before care arrived. About 25 percent of people who have a ruptured aneurysm die within 24 hours, and another 25 percent have complications that lead to death within six months [2].
How can you lower your risk?
Many brain aneurysms cannot be prevented, but certain lifestyle changes can lower the risk of one forming or rupturing [1].
Step | How it helps |
Quit smoking | Smoking raises the risk of both forming and rupturing an aneurysm; quitting programs are available |
Manage blood pressure | Working with a healthcare professional to lower high blood pressure protects weakened arteries |
Eat a healthy diet and exercise | Diet and exercise changes can help lower blood pressure |
Avoid excess alcohol | Heavy drinking can raise blood pressure |
Avoid recreational drugs | Substances such as cocaine and methamphetamine raise blood pressure and damage blood vessels |
When should you see a specialist about a brain aneurysm?
If test results show a brain aneurysm, you will need a specialist in brain and nervous system conditions, such as a neurologist, neurosurgeon, or neuroradiologist. Write down all symptoms, major stresses or life changes, and all medicines, vitamins, and supplements with doses; bring a family member or friend; and list questions in order of importance [2].
What is known about the aneurysm's size, location, and appearance, and how likely is it to rupture? [2]
What treatment is recommended now, and what are its risks? If none yet, how often are follow-up scans needed? [2]
What steps lower the risk of rupture? [2]
Expect questions about smoking, alcohol and drug use, blood pressure treatment, whether medicines are taken as prescribed, and family history of aneurysm or rupture [2]
What is the bottom line on brain aneurysms?
Most brain aneurysms are small, silent, and never rupture — but a rupture is a medical emergency where every minute counts. Know the warning sign (a sudden, extremely severe headache), manage blood pressure, avoid smoking, and talk with a neurologist about whether treatment or watchful waiting is the safer path if you have an unruptured aneurysm [1] [2].
Next steps: If you or someone you know has a sudden, extremely severe headache, call 911 or your local emergency number immediately. If you have a family history of aneurysm or a condition that raises risk, ask a healthcare professional whether screening is right for you.
Frequently asked questions
What is the most common symptom of a ruptured brain aneurysm?
A sudden, extremely severe headache, often described as the worst headache of the person's life, typically with nausea, a stiff neck, vision changes, confusion, or loss of consciousness [1].
Can a brain aneurysm leak before it ruptures?
Yes. An aneurysm can leak a small amount of blood days or up to two weeks before a full rupture, often causing a sudden, extremely severe headache that lasts several days to two weeks [1].
Do all brain aneurysms need treatment?
No. Most are small, never rupture, and cause no symptoms. For unruptured aneurysms, doctors weigh the low rupture risk against the risks of procedures; sometimes watchful waiting with regular scans is the safest choice [2].
What is the difference between surgical clipping and coiling?
Clipping opens the skull and places a tiny metal clip on the aneurysm's neck; clipped aneurysms usually do not return. Coiling threads a catheter through an artery to pack a spiral coil inside the aneurysm; it is less invasive, but the aneurysm can recur and follow-up imaging is needed [2].
Who should get screened for a brain aneurysm?
Screening is generally reserved for people at high risk, including those with a family history of aneurysms or hemorrhagic stroke (especially two or more first-degree relatives) and people with polycystic kidney disease, coarctation of the aorta, or Ehlers-Danlos syndrome [2].
This article is educational and is not a substitute for professional medical advice, diagnosis, or treatment. If you have a sudden, severe headache, seek emergency care immediately.
What should I do if I think someone has a ruptured brain aneurysm?
Call 911 or your local emergency number right away. Do not drive the person yourself or wait to see if the headache improves. Fast treatment gives the best chance of survival and recovery.
What are the signs of an unruptured brain aneurysm?
Most cause no symptoms. A larger one that presses on nerves may cause pain above and behind one eye, a widened pupil, double vision or other vision changes, or numbness on one side of the face. See a provider promptly for these symptoms.
What raises the risk of a brain aneurysm?
Smoking, high blood pressure, heavy alcohol use and drugs such as cocaine raise the risk. Being female, being 30 to 60 years old, polycystic kidney disease and a family history also play a role.
Can I lower my risk of a brain aneurysm rupturing?
Yes. Quitting smoking, keeping blood pressure under control, limiting alcohol and avoiding drugs like cocaine and methamphetamine all help. Ask your provider how often you need follow-up scans if you have an aneurysm.
What is a flow diverter?
A flow diverter is a tiny mesh tube placed inside the artery through a catheter. It steers blood away from the aneurysm so it slowly seals off and is less likely to burst.
Related Reading
MRI (Magnetic Resonance Imaging): Uses, What to Expect, Safety and Results: MRI and magnetic resonance angiography (MRA) image the brain and its blood vessels to help find aneurysms, narrowing or blockages.
Learn more in our guide to CT Angiogram (CTA): What It Shows, How to Prepare and What to Expect.
MRA (Magnetic Resonance Angiography): What It Is, Why It's Done, Procedure and Results explains how magnetic resonance angiography makes detailed pictures of your blood vessels without X-ray radiation.
Brain MRI: Why It's Done, How to Prepare and What to Expect explains what a brain MRI shows and what to expect during the scan.
Cerebral Angiogram: What It Shows, How to Prepare, What to Expect, Risks and Recovery explains how a catheter and contrast dye show the brain's blood vessels, how to prepare and the risks.
References
Mayo Clinic Staff. Brain aneurysm - Symptoms and causes. Mayo Clinic. August 19, 2026. https://www.mayoclinic.org/diseases-conditions/brain-aneurysm/symptoms-causes/syc-20361483
Mayo Clinic Staff. Brain aneurysm - Diagnosis and treatment. Mayo Clinic. August 19, 2026. https://www.mayoclinic.org/diseases-conditions/brain-aneurysm/diagnosis-treatment/drc-20361595
Dremel J, et al. Prevalence of unruptured intracranial aneurysms according to comorbidities, risk factors, country, and time period: a systematic review and meta-analysis. Lancet Neurol. 2026;25(10):911-925. PMID 42679840. https://doi.org/10.1016/S1474-4422(26)00276-0
Ahmed A, et al. Woven endobridge device compared to stent-assisted coiling and microsurgical clipping for intracranial aneurysms: A systematic review and meta-analysis. Medicine (Baltimore). 2026;105(35):e50462. PMID 42675776. https://doi.org/10.1097/MD.0000000000050462
Hu X, et al. Tirofiban for Reduction of Thromboembolic Events in Endovascular Unruptured Aneurysm Repair (TEAR): A Phase 2, Randomized, Open-Label, Blinded End Point, Controlled Trial. Stroke. 2026;57(8):2295-2304. PMID 42283072. https://doi.org/10.1161/STROKEAHA.126.056558
Brain Aneurysm Foundation. Home. Brain Aneurysm Foundation. Accessed October 15, 2026. https://www.bafound.org
American Stroke Association. American Stroke Association. American Stroke Association. Accessed October 15, 2026. https://www.stroke.org
Centers for Disease Control and Prevention. Signs and Symptoms of Stroke. Centers for Disease Control and Prevention. May 19, 2026. https://www.cdc.gov/stroke/signs-symptoms/index.html
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