Cerebral Aneurysm

A cerebral aneurysm (also known as a brain aneurysm) is a weak or thin spot on an artery in the brain that balloons or bulges out and fills with blood. The bulging aneurysm can put pressure on the nerves or brain tissue. It may also burst or rupture, spilling blood into the surrounding tissue (called a hemorrhage). A ruptured aneurysm can cause serious health problems such as hemorrhagic stroke, brain damage, coma and even death.

There are three types of cerebral aneurysms:

• Saccular aneurysm. A saccular aneurysm is a rounded sac containing blood that is attached to a main artery or one of its branches. Also known as a berry aneurysm (because it resembles a berry hanging from a vine), this is the most common form of cerebral aneurysm. It is typically found on arteries at the base of the brain. Saccular aneurysms occur most often in adults.
• Fusiform aneurysm. A fusiform aneurysm balloons or bulges out on all sides of the artery.
• Mycotic aneurysm. A mycotic aneurysm occurs as the result of an infection that can sometimes affect the arteries in the brain. The infection weakens the artery wall, causing a bulging aneurysm to form. 

Aneurysms are also classified by size: small, large and giant:

• Small aneurysms are less than 11 millimeters in diameter (about the size of a large pencil eraser).
• Large aneurysms are 11 to 25 millimeters (about the width of a dime).
• Giant aneurysms are greater than 25 millimeters in diameter (more than the width of a quarter).

Most cerebral aneurysms are acquired lesions, with an increased incidence in patients with risk factors like advanced age, hypertension, smoking, alcohol abuse and atherosclerosis. Other causes include cocaine use, tumors, trauma and certain embolic-forming infections like endocarditis.

There is also a strong genetic element with significantly increased risk in patients with a strong family history of aneurysms (in other words, more than one family member affected). Certain genetic conditions are associated with higher prevalence. This includes, but is not limited to, autosomal dominant polycystic kidney disease, Ehlers-Danlos syndrome, fibromuscular dysplasia, tuberous sclerosis, arteriovenous malformations (AVM) and coarctation of the aorta.

Cerebral aneurysms form when the walls of the arteries in the brain become thin and weaken. Aneurysms typically form at branch points in arteries because these sections are the weakest. Occasionally, cerebral aneurysms may be present from birth, usually resulting from an abnormality in an artery wall. 

Brain aneurysms can occur in anyone and at any age. They are most common in adults between the ages of 30 and 60 and are more common in women than in men. People with certain inherited disorders are also at higher risk.

Scientists have long known about the link between cerebral and aortic aneurysm (the aorta is the body’s main artery). However, they still do not fully understand the relationship between the two types of aneurysm. Recent genome-wide association studies (GWAS) provide molecular evidence for shared biological function and activities (pathophysiology) of these aneurysms. A specific site on chromosome 9p21 has been identified as increasing the risk for both cerebral and aortic aneurysms. This GWAS data, along with linkage data to other susceptible locations for genes or DNA sequences, indicate that individuals and families harboring one type of aneurysm may be at especially increased risk of the other.

Sometimes cerebral aneurysms are the result of inherited risk factors, including:

• Genetic connective tissue disorders that weaken artery walls
• Polycystic kidney disease (in which numerous cysts form in the kidneys)
• Arteriovenous malformations. Snarled tangles of arteries and veins in the brain that disrupt blood flow. Some AVMs develop sporadically, or on their own.
• History of aneurysm in a first-degree family member (child, sibling or parent)

Other risk factors develop over time and include:

• Untreated high blood pressure
• Cigarette smoking
• Drug abuse, especially cocaine or amphetamines, which raise blood pressure to dangerous levels. Intravenous drug abuse is a cause of infectious mycotic aneurysms
• Age over 40

Less common risk factors include:

• Head trauma
• Brain tumor
• Infection in the arterial wall (mycotic aneurysm)

Additionally, high blood pressure, cigarette smoking, diabetes and high cholesterol put one at risk of atherosclerosis (a blood vessel disease in which fats build up on the inside of artery walls), which can increase the risk of developing a fusiform aneurysm.

Not all aneurysms will rupture. Aneurysm characteristics such as size, location and growth during follow-up evaluation may affect the risk that an aneurysm will rupture. In addition, medical conditions may influence aneurysm rupture.

Risk factors include:

• Smoking: Smoking is linked to both the development and rupture of cerebral aneurysms. Smoking may even cause multiple aneurysms to form in the brain.
• High blood pressure: High blood pressure damages and weakens arteries, making them more likely to form and to rupture.
• Size: The largest aneurysms are the ones most likely to rupture in a person who previously did not show symptoms.
• Location: Aneurysms located on the posterior communicating arteries (a pair of arteries in the back part of the brain) and possibly those on the anterior communicating artery (a single artery in the front of the brain) have a higher risk of rupturing than those at other locations in the brain.
• Growth: Aneurysms that grow, even if they are small, are at increased risk of rupture.
• Family history: A family history of aneurysm rupture suggests a higher risk of rupture for aneurysms detected in family members.
• The greatest risk occurs in individuals with multiple aneurysms who have already suffered a previous rupture or sentinel bleed.

Magnetic resonance angiography (CT) and magnetic resonance angiography (MRI) scans are typically used to detect brain aneurysms. These tests produce images of the brain that caregivers can use to detect blockages or other brain abnormalities.

Preventing aneurysms from growing or rupturing is to avoid any activities that could damage blood vessels. Eating a healthy diet and not smoking are both helpful in preventing cerebral aneurysms.

Most cerebral aneurysms go unnoticed until they rupture or are detected during medical imaging tests for another condition.

If you have experienced a severe headache or have any other symptoms related to a ruptured aneurysm, your doctor will order tests to determine if blood has leaked into the space between the skull bone and brain.

Several tests are available to diagnose brain aneurysms and determine the best treatment. These include:

• Computed tomography (CT). This is often the first test a physician will order to determine if blood has leaked into the brain. CT uses X-rays to create two-dimensional images, or “slices,” of the brain and skull. Occasionally, a contrast dye is injected into the bloodstream prior to scanning to assess the arteries and look for a possible aneurysm. This process, called CT angiography (CTA), produces sharper, more detailed images of blood flow in the brain arteries. CTA can show the size, location and shape of an unruptured or a ruptured aneurysm.
• Magnetic resonance imaging (MRI). An MRI uses computer-generated radio waves and a magnetic field to create two- and three-dimensional detailed images of the brain and can determine if there has been bleeding into the brain. Magnetic resonance angiography (MRA) produces detailed images of the brain arteries and can show the size, location and shape of an aneurysm.
• Cerebral angiography. This imaging technique can find blockages in arteries in the brain or neck. It also can identify weak spots in an artery, like an aneurysm. The test is used to determine the cause of the bleeding in the brain and the exact location, size and shape of an aneurysm. Your doctor will pass a catheter (long, flexible tube), typically from the groin arteries, to inject a small amount of contrast dye into your neck and brain arteries. The contrast dye helps the X-ray create a detailed picture of the appearance of an aneurysm and a clear picture of any blockage in the arteries.
• Cerebrospinal fluid (CSF) analysis. This test measures the chemicals in the fluid that cushions and protects the brain and spinal cord (cerebrospinal fluid). Most often a doctor will collect the CSF by performing a spinal tap (lumbar puncture), in which a thin needle is inserted into the lower back (lumbar spine) and a small amount of fluid is removed and tested. The results will help detect any bleeding around the brain. If bleeding is detected, additional tests would be needed to identify the exact cause of the bleeding.

Cerebral aneurysms located at the posterior communicating artery and in the arteries in the back part of the brain (called the vertebral and basilar arteries) are common and have higher risk of rupture than aneurysms at other locations. NINDS-funded scientists are working to identify the features associated with rupture and use these factors to build a scoring scale to guide and support clinical decisions.

The risk of having an aneurysm burst is difficult to determine, and there can be serious complications from surgical treatments. Researchers are developing a new model to diagnose brain aneurysms based on the presence of molecules that can potentially tell whether there is a high chance of an aneurysm burst. This procedure can be done by using brain imaging without the need to open the skull. Not only would this new tool be less invasive, it would also allow for people to be treated before an aneurysm bursts.

Not all cerebral aneurysms require treatment. Some very small, unruptured aneurysms that are not associated with any factors suggesting a higher risk of rupture may be safely left alone and monitored with magnetic resonance angiography (MRA) or computed tomography angiography (CTA) to detect any growth. It is important to aggressively treat any coexisting medical problems and risk factors.

Studies indicate that aspirin lessens inflammation in cerebral aneurysms and reduces the risk of rupture. However, aspirin also inhibits the blood cells (platelets) that are important in stopping bleeding once a rupture occurs. Researchers are using mouse models to examine how inflammation impacts the formation and rupture of cerebral aneurysms, and the molecular mechanisms that contribute to the protective effect of aspirin.

Cerebral aneurysms and subarachnoid hemorrhage are more common in postmenopausal women than in men. Estrogen replacement therapy reduces the risk for subarachnoid hemorrhage in postmenopausal women. Researchers are investigating exactly how estrogen protects women against developing aneurysms. They hypothesize that protection primarily occurs through inflammatory cells.

Other research projects include studies of the effectiveness of microsurgical clipping and endovascular surgery to treat ruptured and unruptured aneurysms, the use of various types of coils and other materials to block the flow of blood into the aneurysm, and the influence of blood flow speed and pressure on the success or failure of treatment.

Treatments for unruptured cerebral aneurysms that have not shown symptoms have some potentially serious complications and should be carefully weighed against the predicted rupture risk.

A doctor will consider a variety of factors when determining the best option for treating an unruptured aneurysm, including:

• type, size and location of the aneurysm
• risk of rupture
• the person’s age and health
• personal and family medical history
• risk of treatment

Individuals should also take the following steps to reduce the risk of aneurysm rupture:

• carefully control blood pressure
• stop smoking
• avoid use of cocaine or other stimulant drugs

Around 25 percent of people who suffer a cerebral aneurysm will die within 24 hours of a rupture. Up to 50 percent will experience complications that lead to death within three months of rupture. Survivors of ruptured cerebral aneurysms live with permanent brain damage, requiring high levels of care.  

To further your understanding of your diagnosis and to contribute to cutting-edge research, consider participating in a clinical trial so clinicians and scientists can learn more about causes, symptoms, treatment and prevention. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.

For information about participating in clinical research, visit NIH Clinical Research Trials and You. Learn about clinical trials currently looking for participants at Clinicaltrials.gov.