Aneurysms may occur in any artery. (See also Aortic Branch Aneurysms Aortic Branch Aneurysms Aortic branch aneurysms are bulges (dilations) in the wall of the major arteries that come directly off of the aorta. (See also Overview of Aortic Aneurysms and Aortic Dissection.) The aorta... read more and Aneurysms of Arteries in the Arms, Legs, and Heart Aneurysms of Arteries in the Arms, Legs, and Heart An aneurysm is a bulge (dilation) in the wall of an artery. (See also Aortic Branch Aneurysms and Brain Aneurysms.) Aneurysms may occur in any artery. Aneurysms are most common in the aorta... read more .)
In the United States, brain aneurysms occur in 3 to 5% of people. Brain aneurysms can occur at any age but are most common among people aged 30 to 60 years. They are more common among women than men.
People may have only one cerebral aneurysm or several.
Causes of Brain Aneurysms
Many cerebral aneurysms result from a weakness in the artery wall that is present at birth (congenital). Others are caused by atherosclerosis Atherosclerosis Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more 
(buildup of plaque or fatty material in the wall of blood vessels).
Other aneurysms result from bacterial or fungal infections in the wall of the artery that develop after use of illicit intravenous drugs such as heroin. Such infections usually start elsewhere in the body, typically in a heart valve Infective Endocarditis Infective endocarditis is an infection of the lining of the heart (endocardium) and usually also of the heart valves. Infective endocarditis occurs when bacteria enter the bloodstream and travel... read more 
, before spreading to the wall of the artery.
Factors that increase the risk of having a brain aneurysms may include
Hereditary connective tissue disorders Overview of Connective Tissue Disorders in Children Connective tissue is the tough, often fibrous tissue that binds the body's structures together and provides support and elasticity. Muscles, bones, cartilage, ligaments, and tendons are built... read more (such as Ehlers-Danlos syndromes Ehlers-Danlos Syndromes Ehlers-Danlos syndromes are rare hereditary disorders of connective tissue that result in unusually flexible joints, very elastic skin, and fragile tissues. These syndromes are caused by a defect... read more
, pseudoxanthoma elasticum Pseudoxanthoma Elasticum Pseudoxanthoma elasticum is a rare hereditary disorder of connective tissue that causes abnormalities in the skin, eyes, and blood vessels. Connective tissue is the tough, often fibrous tissue... read more 
, and autosomal dominant polycystic kidney syndrome Polycystic Kidney Disease (PKD) Polycystic kidney disease is a hereditary disorder in which many fluid-filled sacs (cysts) form in both kidneys. The kidneys grow larger but have less functioning tissue. Polycystic kidney disease... read more )A first-degree relative (parent, sibling, or child) who has had an aneurysm
Cigarette smoking
A substance use disorder
Symptoms of Brain Aneurysms
Most cerebral aneurysms do not cause symptoms unless they are large or rupture.
Larger unruptured cerebral aneurysms can push on brain tissue and nerves and cause headache, which may feel pounding in time with the pulse (pulsatile). Less often, people may have dilated pupils and/or symptoms of a stroke, such as weakness or paralysis on one side of the body. People with aneurysms caused by bacterial or fungal infection may have a fever and lose weight.
Rupture of a cerebral aneurysm causes a subarachnoid hemorrhage Subarachnoid Hemorrhage (SAH) A subarachnoid hemorrhage is bleeding into the space (subarachnoid space) between the inner layer (pia mater) and middle layer (arachnoid mater) of the tissues covering the brain (meninges)... read more 
with an immediate, severe headache. The pain reaches its peak intensity within seconds. It is sometimes described as coming on like a thunderclap and "the worst headache ever experienced." A ruptured aneurysm may also cause nausea, vomiting, a stiff neck, sensitivity to light, loss of consciousness, and/or seizures.
If the ruptured aneurysm bleeds into the brain tissue (intracerebral hemorrhage Intracerebral Hemorrhage An intracerebral hemorrhage is bleeding within the brain. Intracerebral hemorrhage usually results from chronic high blood pressure. The first symptom is often a severe headache. Diagnosis is... read more ), people often develop a symptoms of a stroke Symptoms A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more (which is typically caused by blood clots rather than bleeding). The bleeding can increase the pressure in the brain, which can lead to coma and sometimes death.
Diagnosis of Brain Aneurysms
Computed tomography (CT) angiography or magnetic resonance angiography
Because cerebral aneurysms are near the brain and are usually small, their diagnosis and treatment differ from those of other aneurysms.
Brain aneurysms may be detected incidentally when imaging tests are done for other reasons.
The diagnosis of a brain aneurysm is based on results of computed tomography (CT) angiography CT angiography Computed tomography (CT) is a type of medical imaging that combines a series of x-rays to create cross-sectional, detailed images of internal structures. In computed tomography (CT), which used... read more 
(CT done after a contrast agent is injected into a vein) or magnetic resonance angiography Magnetic resonance angiography (MRA) Magnetic resonance imaging (MRI) is a type of medical imaging that uses a strong magnetic field and very high frequency radio waves to produce highly detailed images. During an MRI, a computer... read more 
. However, digital subtraction angiography Digital subtraction angiography Angiography is a type of medical imaging that uses x-rays and a contrast agent to produce images of blood vessels. In angiography, x-rays are used to produce detailed images of blood vessels... read more is the most accurate way to diagnose aneurysms.
For digital subtraction angiography, x-ray images of blood vessels are taken before and after a radiopaque contrast agent is injected. Then a computer subtracts one image from the other. Images of structures other than arteries (such as bones) are eliminated. As a result, the arteries can be seen more clearly.
Tests used to diagnose an infected aneurysm include CT angiography or magnetic resonance angiography and blood cultures. which can show the growth of microorganisms (such as bacteria or fungi).
Treatment of Brain Aneurysms
For small unruptured aneurysms, regular imaging tests to monitor growth
For large unruptured aneurysms, surgical or catheter-based repair
Treatment of unruptured aneurysms depends on
Type, size, and location of the aneurysm
Risk of rupture
The person's age and health
Medical history of the person and family members to check for previous aneurysms and risk factors for them
Risks of treatment
Doctors discuss the risks of treatment compared with those of possible rupture so that the person can make an informed decision.
Control of risk factors for atherosclerosis Risk Factors for Atherosclerosis Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more , especially smoking cessation and use of antihypertensive medications, is important.
If the risk of rupture is low, the only measure needed may be regular monitoring of the aneurysm.
If the aneurysm is large or is causing symptoms, treatment often involves surgical repair. One of the following surgical procedures (called endovascular surgery) is used to repair an aneurysm:
Endovascular coiling
Endovascular stenting
Endovascular coiling, a less invasive treatment, is commonly used. It involves inserting coiled wires into the aneurysm. For this procedure, a catheter is inserted into an artery, usually in the groin, and threaded to the affected artery in the brain. A contrast agent is injected to enable the doctor to make the aneurysm visible on an x-ray. The catheter is then used to place the coils in the aneurysm. Thus, this procedure does not require that the skull be opened. By slowing blood flow through the aneurysm, the coils encourage the formation of blood clots, which seals off the aneurysm and prevents it from rupturing. Endovascular coils can be placed at the same time as cerebral angiography, when the aneurysm is diagnosed. The coils remain in place permanently.
In endovascular stenting, a catheter is used to place a tube made of wire (stent) across the opening of the aneurysm. The stent reroutes normal blood flow around the aneurysm, preventing blood from entering the aneurysm and eliminates the risk of rupture. The stent remains in place permanently.
Less commonly, a metal clip is placed across the aneurysm. For this procedure, surgeons make an incision in the skin of the head and remove a piece of the skull so that they can see the aneurysm. The clip is then placed across the opening of the aneurysm. This procedure prevents blood from entering the aneurysm and eliminates the risk of rupture. The clip remains in place permanently. Surgical placement of a clip requires spending several nights in the hospital.
When the aneurysm is infected, antibiotics or antifungal medications are given.
If the aneurysm has ruptured, digital subtraction angiography is used to locate it, then endovascular or open surgery is done.
