Brain Aneurysm

What Facts Should I Know About a Brain Aneurysm?

Doctors exam the malfunction of human brain.
Doctors exam the malfunction of human brain by iStock

A brain aneurysm is a bulge or ballooning out of a blood vessel in the brain, most often resembling a berry (they are also termed berry aneurysms or cerebral aneurysms). Unfortunately, the walls of the aneurysm are not as stable as normal blood vessel walls. Consequently, brain aneurysms under certain conditions may rupture and allow blood to leak into surrounding tissues.


  • There are two main types of brain aneurysms: saccular and fusiform aneurysms.
  • Symptoms develop rapidly when an aneurysm ruptures.
  • Ruptured aneurysms are medical emergencies; patients with suspected ruptured aneurysms should be seen immediately in emergency departments that have neurosurgeons on call (usually hospitals that handle major trauma have neurosurgeons on call).

What Are the Different Kinds of Brain Aneurysms?

There are two main types of brain aneurysms -- saccular (berry) aneurysms and fusiform aneurysms. The most common type of aneurysm is saccular. Saccular or berry aneurysms look like a sack and are usually formed at the bifurcation or “Y” formation when a larger vessel splits into two vessels. These types of aneurysms are often found at the branches of larger arteries at the base of brain but may be found in other areas of the brain, too.

The second type, a fusiform aneurysm, is less common than a saccular aneurysm and is more stable and seldom ruptures. Fusiform aneurysms occur at the junction of the “Y” formation where a blood vessel branches and extends into both smaller vessels and also into the single larger vessel. Fusiform aneurysms don't develop any stems like saccular aneurysms.

What Causes a Brain Aneurysm?

The development of brain aneurysms is considered a controversial topic. Currently, most researchers think that a combination of factors, both genetic and environmental, lead to the development of brain aneurysms. For example, some aneurysms may have a strong genetic component that is inherited (for example, individuals with polycystic kidney disease and arteriovenous malformations are more likely to develop aneurysms). However, environmental pressures such as hypertension are also associated with brain aneurysm development. In addition, some aneurysms are associated with environmental factors like infections or trauma.

Who Is at Risk for a Brain Aneurysm?

There are a number of medical conditions that increase risk for brain aneurysms. Individuals with the following conditions are at higher risk -- polycystic kidney disease, fibromuscular dysplasia, arteriovenous malformations, lupus, sickle cell anemia, bacterial endocarditis, fungal infections, hypertension, cancers, cigarette smoking, alcohol use, illicit drug use, head trauma, and syndromes that involve connective or elastic tissue problems (for example, collagen disorders). Women are more likely to develop brain aneurysms than men (the ratio is 3 to 2). This list represents many people who are at higher risk for brain aneurysms, but it does not include every possible risk factor.

What Are the Signs and Symptoms of a Brain Aneurysm?

Most brain aneurysms do not cause any signs or symptoms and are discovered during tests for another condition. Symptoms develop rapidly when an aneurysm ruptures, and in some cases symptoms can be caused by pressure from an unruptured anuerysm. The signs and symptoms of a brain aneurysm are variable and occasionally relate to the area of the brain that is affected. However, the most common symptom of a ruptured brain aneurysm is headache and is characterized by the patient describing the headache as “the worst headache of my life.” However, some patients don't report headache as a symptom. The following is a list of possible symptoms that are seen in patients with a brain aneurysm:

  • visual defects
  • facial pain
  • focal neurological complaints
  • seizures
  • passing out or fainting
  • confusion or mental impairment
  • nausea and/or vomiting
  • cardiac dysrhythmias
  • neck pain or stiffness
  • photophobia
  • trouble breathing
  • nosebleeds
  • dilated pupils
  • stroke-like symptoms (loss of speech, loss of sense of smell, paralysis of muscles on one side of the body, or other movement defects)

How Do Doctors Diagnose a Brain Aneurysm?

In most instances, the diagnosis of a brain aneurysm is made by CT scan and/or MRI imaging studies of the brain. These tests help identify and localize the brain aneurysm. Other tests such as a cerebral angiogram and/or a cerebrospinal fluid analysis may also be used to help determine the diagnosis. In addition, transcranial Doppler ultrasonography and single-photon emission computed tomography (SPECT) may be used to examine blood flow within the brain. Laboratory tests that are almost always ordered are a complete blood cell count (CBC), prothrombin time (PT), activated partial thromboplastin time (a PTT), serum chemistries, liver function tests, and arterial blood gases. These tests help determine if the patient is anemic and/or prone to bleeding and help determine if the patient's blood is getting appropriate oxygenation.

What Is the Treatment for a Brain Aneurysm?

Treatment for unruptured intracranial aneurysms is very controversial. Some investigators suggest that aneurysms less than 10 mm be left alone while those larger than that should be considered for treatment in patients less than 50 years old. The controversy lies in the surgical mortality and morbidity of surgically treated aneurysms. The mortality (death) rate is 1.7% and the morbidity (development of complications) is 6.7%. Many investigators suggest that aneurysms larger than 10 mm that are not associated with symptoms should be considered for treatment, especially in patients with coexisting medical conditions. Surgical treatment (clipping, in which the surgeon places a clip at the base of the aneurysm) is less likely in patients who have poor health or other serious medical conditions. Endovascular therapy or coiling (in which a small thin platinum wire is coiled into the aneurysm by a catheter in the blood vessel) is another surgical technique that can result in obliteration of the aneurysm. The goal of treatment for unruptured intracranial aneurysms is to prevent bleeding into the brain.

Ongoing bleeding of a brain aneurysm usually requires consultation with a neurosurgeon, interventional radiologist, and/or a neurologist. These individuals decide if surgery or interventional therapies such as coiling will be of benefit to the patient. For example, the neurosurgeon may decide to suction blood out of the area if it's not too large and hasn't caused catastrophic brain damage. Bleeding from a brain aneurysm is a medical emergency. Medical treatments for brain aneurysms that have bled are designed to reduce and/or alleviate symptoms. Nimodipine is used to prevent or relieve abnormal spasms of the arteries within the brain. Anti-epileptic drugs like phenytoin are used to treat and prevent seizures. Antihypertensive medications like labetalol can help reduce pressure on the blood vessel walls in the brain to lessen the chance of bleeding.

What Is the Survival Rate and Prognosis for a Brain Aneurysm?

Researchers estimate that about 6 million people in United States have an unruptured brain aneurysm, and about 10% to 15% of these people will have more than one brain aneurysm. Someone with an unruptured brain aneurysm has about a 1% chance of the aneurysm rupturing per year. Patients with “giant” aneurysms (1 inch or greater in diameter) have a much higher risk of rupture. The survival rate for those with a ruptured brain aneurysm is about 60% (40% die). For those who survive and recover, about 66% have some permanent neurological defect. In summary, patients with small brain aneurysms that do not rupture (about 80%) have a very good prognosis while those who suffer a rupture have a fair to poor prognosis.

Is It Possible to Prevent a Brain Aneurysm?

Most brain aneurysms cannot be prevented; however, certain types of lifestyle modification -- such as avoiding illicit drugs and overuse of alcohol -- may reduce the risk of a brain aneurysm. Some brain aneurysms may be treated with surgical techniques that reduce the risk of rupture.

Brain Aneurysm Signs and Symptoms

Symptoms of a ruptured brain aneurysm often come on suddenly. If you have any of the following symptoms or notice them in someone you know, call or other emergency services right away:

  • A sudden, severe headache that is different from past headaches.
  • Neck pain.
  • Nausea and vomiting.
  • Sensitivity to light.
  • Fainting or loss of consciousness.
  • Seizures.
Medically reviewed by Jon Glass, MD; American Board of Psychiatry and Neurology


"Understanding: Brain Aneurysm Basics." Brain Aneurysm Foundation.

"Understanding: Brain Aneurysm Statistics and Facts." Brain Aneurysm Foundation.

Liebeskind, D.S., et al. "Cerebral Aneurysms." Medscape. July 8, 2013.