What is Brain Aneurysm and How It's Caused

A brain aneurysm is a weak, bulging spot in a brain artery that can leak or burst, causing bleeding around the brain called a subarachnoid hemorrhage, which is a medical emergency that needs immediate care. The main causes are wear-and-tear changes in artery walls plus risk factors like high blood pressure, smoking, family history, and certain genetic conditions such as polycystic kidney disease and connective tissue disorders.

Most aneurysms are small and never cause symptoms, but a rupture typically triggers a “thunderclap” headache—often described as the worst headache of one’s life—along with other warning signs. When an aneurysm bursts, it causes bleeding in the brain, leading to a type of stroke called a subarachnoid hemorrhage.

Why Do Aneurysms Form?

Aneurysms form where artery walls are weak, often at branching points, and years of pulsating blood flow can stretch the area into a thin-walled bulge. High blood pressure, smoking, age, female sex, and inherited conditions can further weaken vessel walls and increase the chance an aneurysm will develop or rupture.

How Common Are Brain Aneurysms?

Roughly one in fifty people in the United States has an unruptured brain aneurysm, and tens of thousands experience a rupture each year. Worldwide, hundreds of thousands of deaths are linked to aneurysm-related bleeding annually, highlighting why recognition and rapid treatment matter.

Types of Brain Aneurysms

Brain aneurysms come in different shapes and sizes, and understanding these variations helps medical professionals assess risk and determine treatment approaches:

Saccular Aneurysms (Berry Aneurysms): These are the most common type, accounting for about 90% of all brain aneurysms. They look like a round berry hanging from a stem attached to an artery. The "neck" of the aneurysm connects to the parent artery, while the dome contains the bulging sac of blood.

Fusiform Aneurysms: Unlike saccular aneurysms, fusiform aneurysms don't have a distinct neck. Instead, they cause the artery to bulge outward on all sides, creating a spindle-shaped dilation. These are less common but can be more challenging to treat.

Mycotic Aneurysms: These rare aneurysms develop as a result of infection that weakens the arterial wall. Despite the name, they're typically caused by bacteria rather than fungi.

Who is at High Risk of Brain Aneurysms

In addition to genetic conditions like polycystic kidney disease and certain connective tissue disorders, smoking, high blood pressure, heavy drinking, stimulant drugs like cocaine, aging, and being female all increase risk. Candidates for screening could include people with qualifying genetic disorders or two or more close relatives with aneurysm history.

What Are the Symptoms of a Ruptured Aneurysm?

A ruptured aneurysm usually causes a sudden, severe “thunderclap” headache, often with nausea, vomiting, neck stiffness, confusion, fainting, seizures, or sensitivity to light. This bleeding in the space around the brain is called a subarachnoid hemorrhage, a type of stroke that requires emergency care.

Symptoms of An Unruptured Aneurysm?

Many unruptured aneurysms cause no symptoms, but larger ones can press on nearby nerves and tissues, leading to eye pain, drooping eyelid, double vision, or localized weakness or numbness. New or worsening localized neurologic changes—especially around one eye—also warrant prompt medical attention.

Difference Between Migraine and Brain Aneurysm

Migraine headaches typically build gradually, while aneurysm-related “thunderclap” headaches strike instantly and can be accompanied by loss of consciousness or seizures, which are not typical for migraine. Any sudden, worst-ever headache—especially with other neurologic symptoms—should be treated as an emergency.

What Happens After a Rupture?

A rupture causes blood to leak around the brain, which can lead to swelling and further damage by raising blood pressure, stimulating blood vessels, and occasionally obstructing the passage of cerebrospinal fluid. Vasospasm (blood vessel narrowing), hydrocephalus (fluid accumulation), rebleeding, electrolyte imbalances, and seizures are among the complications that might occur and are treated in critical care.

How Are Brain Aneurysms Diagnosed?

Brain aneurysms are typically diagnosed through imaging tests. If doctors suspect an aneurysm based on symptoms or family history, they may order:

CT Scan (Computed Tomography): A quick imaging test that can detect bleeding in the brain and is often the first test performed in emergency situations.

MRI (Magnetic Resonance Imaging): Provides detailed images of the brain and blood vessels without radiation exposure.

CT or MR Angiography: These specialized scans focus on blood vessels and can show the size, shape, and location of aneurysms.

Cerebral Angiogram: Considered the gold standard for diagnosing brain aneurysms, this procedure involves injecting contrast dye into the bloodstream and taking X-ray images of the brain's blood vessels.

How Are Brain Aneurysms Treated?

Treatment aims to prevent bleeding or rebleeding by sealing the aneurysm with endovascular coiling (with or without stents), flow-diverting stents for complex cases, or surgical clipping, depending on aneurysm size, shape, and location. Specialized teams select the safest, most effective option for each patient, balancing rupture risk, procedural risk, and individual preferences.

Can Brain Aneurysms Be Prevented?

Not all aneurysms are preventable, but keeping blood pressure under control, quitting smoking, limiting alcohol, avoiding stimulant drugs, and staying active can lower risk. Regular checkups and healthy habits like a balanced diet and stress management support blood vessel health over time.

Conclusion

A brain aneurysm is a weakened, ballooning spot in a brain artery that can quietly exist without symptoms or, if it ruptures, cause a sudden, life-threatening bleed that demands fast treatment. Understanding risk factors, warning signs, and proven treatments—along with healthy daily habits—can lower risk and improve outcomes for both unruptured and ruptured aneurysms.