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Brain Aneurysms: What the Patient Needs to Know

Aaron Cohen-Gadol, M.D.

January 01, 2009

General Aneurysm Information

What Is an Aneurysm?

A brain aneurysm (cerebral aneurysm or intracranial aneurysm) is a small balloon-like or blister-like swelling on the wall of one or more blood vessels supplying the brain. An aneurysm is a result of weakening in the wall of the vessel. This bulge is filled with blood and can cause neurological symptoms when pressed against nerves and/or brain tissues.

Figure 1. Cross-section showing a pericallosal artery aneurysm.

Figure 1. Cross-section showing a pericallosal artery aneurysm.

The most common presentation of a cerebral aneurysm is its rupture and resultant bleeding into the brain. The blood fills the surrounding brain or the area between the brain and arachnoid (a protective membrane surrounding the central nervous system). Such an event is known as an intracerebral hemorrhage or subarachnoid hemorrhage (SAH), depending on the area of the brain affected.

  • Dangers of an aneurysm
  • Types of brain aneurysms
  • Who develops a brain aneurysm
  • What causes a brain aneurysm
  • Hunt-Hess scale

What Are the Dangers of a Brain Aneurysm?

The chief danger of a brain aneurysm is its risk of hemorrhage and the ensuing associated complications. Ruptured aneurysms may cause hemorrhagic stroke, nerve damage, or even death.

Specifically, the blood released from an aneurysm rupture may directly damage brain cells, resulting in a variety of neurological deficits depending on the location of the blood in the brain.

Bleeding may also increase the pressure inside the head (intracranial pressure.) The blood may prevent flow and absorption of normal fluid around and inside the cavities (ventricles) of the brain (cerebrospinal fluid, CSF) resulting in enlarged ventricles and a condition known as hydrocephalus. Hydrocephalus is associated with certain symptoms, such as drowsiness and confusion.

When the blood from the ruptured aneurysm comes into contact with the surrounding arteries supplying the brain, it may cause a condition known as vasospasm. The affected artery constricts in response to the leaked blood, reducing blood flow to the important areas of the brain, possibly causing stroke and brain damage. Vasospasm is often a delayed response to aneurysm bleeding (happens usually after three days of initial bleed) and may occur up to two weeks following the initial bleed.

Types of Brain Aneurysms

Brain aneurysms vary in location and type. Most aneurysms occur at an arterial branch point and are located below the brain and at the base of the skull.

The four major types of aneurysms are:

  • Saccular aneurysms that bulge from one side of an artery
  • Giant aneurysms that are over 2.5 cm wide and may involve multiple arteries
  • Fusiform aneurysms that bulge from all sides of an artery
  • Mycotic aneurysms that are relatively rare and are caused by an infected arterial wall

Figure 2. Saccular aneurysm.

Figure 2. Saccular aneurysm.

Figure 3. Giant aneurysm.

Figure 3. Giant aneurysm.

Figure 4. Fusiform aneurysm.

Figure 4. Fusiform aneurysm.

Who Develops a Brain Aneurysm?

Anyone can develop a brain aneurysm. They are more commonly seen in adults, and women are slightly more at risk than men.

Ruptured aneurysms are seen in ~10 out of every 100,000 people annually in the United States (National Institute of Neurological Disorders and Stroke). Certain pre-existing conditions and behaviors are risk factors for formation of an aneurysm.

Risk factors for aneurysm formation and rupture include:

  • Hypertension
  • Alcohol or drug abuse (especially those drugs which rapidly increase heart rate and blood pressure)
  • Smoking
  • Large aneurysms are more prone to rupture than their smaller counterparts.

What Causes a Brain Aneurysm?

Most aneurysms are the result of degenerative (atherosclerosis) changes or a congenital defect in the arterial wall. Atherosclerosis refers to gradual damage to the wall of vessels with aging. Trauma and certain genetic disorders (especially polycystic kidney disease and disorders of elastic connective tissues) may also lead to a brain aneurysm.

Aneurysms resulting from an infection of the arterial wall (mycotic aneurysms) and aneurysms related to the development of primary or metastatic tumors of the head/neck may also occur.

Other factors which may increase the risk of developing a brain aneurysm include:

  • High blood pressure
  • Certain infections
  • Tumors
  • Atherosclerosis
  • Smoking
  • Drug abuse

My Doctor Refers to the Hunt-Hess Scale. What Is That?

The Hunt-Hess scale is a method by which a doctor (usually a neurologist or neurosurgeon) can refer to the patient's condition. The scale is graded as follows:

Grade I—Alert, aware of surroundings, showing no symptoms
Grade II—Alert, aware of surroundings, has headache, has stiff neck
Grade III—Sluggish or confused, has weakness or partial paralysis on one side of the body
Grade IV—Dazed, has total paralysis on one side of the body
Grade V—Comatose

Adapted from Hunt WE, Hess RM, Surgical risk as related to time of intervention in the repair of intracranial aneurysm. J Neurosurg 28(1): 14-20, 1968.


Not all aneurysms cause problems, and smaller aneurysms are generally asymptomatic.

When an aneurysm ruptures and bleeds, the most common symptom is an extremely severe headache known as a "thunderclap" headache.

Other common symptoms of a ruptured aneurysm are:

  • Brief blackout
  • Nausea and vomiting
  • Vision problems
  • Speech problems
  • Confusion or sluggishness
  • Paralysis or weakness on one side of the body
  • Seizures
  • Clumsiness
  • Sudden changes in cognitive functioning or mood
  • Coma

A person suspected of a brain hemorrhage should seek immediate medical attention.

Larger aneurysms can put pressure on the adjacent nerves and tissues, commonly causing symptoms such as:

  • Pain above and behind the eye
  • Numbness
  • Weakness or paralysis on one side of the face
  • Dilated pupils
  • Vision changes
  • Large aneurysms are also more prone to rupture and hemorrhage.


Your doctor may order several different types of tests if you are suspected of having a cerebral aneurysm or aneurysm rupture. The most common tests include:

  • A CT scan
  • An arteriogram/angiogram
  • A spinal tap

A CT scan is ordered to look for the possibility of blood leaked around and/or into the brain. A CT scan is a series of x-ray images compiled by a computer. When a contrast dye is injected into a vein, a CT scan can also show vasculature.

An arteriogram is frequently done to image the arteries in the brain and look for an aneurysm. A catheter is guided through the groin and via the arteries into the neck, where a contrast dye is released into the brain’s vasculature. An x-ray image is then taken to outline the vasculature and look for an aneurysm.

spinal tap is a third type of test. This is done to look for blood in the patient's cerebrospinal fluid (CSF.) A spinal tap (or lumbar puncture) is done with a needle inserted into the lower spine following application of a local anesthetic.


Options for treatment vary depending on the patient’s age and condition as well as aneurysm’s size, type, and location.

Small, unruptured aneurysms (less than 7mm in maximum dimension) are less prone to rupture and may not be treated, rather, the aneurysm will be carefully monitored with yearly scans to ensure that it does not grow and the risk of rupture does not increase. Aneurysms which rupture and cause bleeding (no matter what size) and aneurysms that are larger than 7mm (even if they have not ruptured) require treatment.

The treatment is highly individualized and depends on the age and medical condition of the patient. If an aneurysm has not ruptured, the risk of bleeding is estimated at 0.5% per year for aneurysms smaller than 7mm and at about 1% per year for aneurysms larger than 7mm.

An aneurysm is treated through either surgery (craniotomy: making a small opening in the skull) or endovascular (using a catheter through the arteries from the groin like the arteriogram and not opening the skull.)

  • Surgery-Craniotomy
  • Endovascular Procedure
  • Hospital Care
  • Other Considerations


Open surgical treatment through craniotomy involves clipping the aneurysm. Your surgeon will remove a small piece of the skull and will go around the brain to place a small titanium clip on the neck of the aneurysm, cutting off its blood flow. This prevents any future bleeding from the aneurysm.

Figure 5. Surgical approach and craniotomy (in blue).

Figure 5. Surgical approach and craniotomy (in blue).

Figure 6. Surgical clipping of a giant posterior communicating artery aneurysm.

Figure 6. Surgical clipping of a giant posterior communicating artery aneurysm.

Alternatively, the surgeon may perform a similar procedure known as an occlusion, in which the entire artery is clipped. Such a procedure is usually necessary when the aneurysm has damaged the blood vessel.

Figure 7. Arterial bypass connecting to the common carotid artery.

Figure 7. Arterial bypass connecting to the common carotid artery.

Because occlusion of an artery cuts off all blood flow through that vessel, a bypass may be performed to restore blood flow to the part of the brain fed by the artery. This involves grafting a small blood vessel to the artery to reroute the flow of blood around the clipped section and past the aneurysm.

Endovascular Procedure

Endovascular procedures avoid the need for directly opening the skull and are instead performed via a catheter guided through the arteries from the groin to the brain. A doctor known as an interventional neuroradiologist will use x-rays to navigate the catheter into the affected artery to release either coils of platinum wire or an inflatable balloon into the aneurysm. The coils or balloon block off the aneurysm and the blood clot forms inside the aneurysm, effectively sealing off the aneurysm.

Hospital Care

If the patient's aneurysm has not bled, following treatment of the aneurysm by surgery or endovascular routes, the patient is observed in the intensive care unit overnight. If there is no complication, he or she is then transferred to the more private less monitored care area to start ambulation and get ready to be discharged in 2-3 days. Anti-seizure medication is administered for at least six months after surgery. Patients may avoid heavy physical activity for six weeks and may return to driving in two weeks.

If the patient's aneurysm has ruptured, following treatment of the aneurysm, the patient will be observed in the intensive care unit for at least nine days. During this period, the patient will be carefully monitored for any signs of neurological change possibly related to vasospasm (clamping of normal brain vessels due to the residual blood around the brain vessels causing stroke.) If the patient remains in good neurological condition, he or she will be transferred to a less monitored unit and will have more privacy. Rehabilitation-the next and the most important part of treatment-then begins.

Other Considerations

The problems associated with brain aneurysms and subarachnoid hemorrhage have a variety of treatments. For the increased intracranial pressure caused by subarachnoid hemorrhage, a shunt or drain may be placed in the ventricles or skull to relieve the pressure of fluid build-up.

Appropriate drugs may be administered to prevent vasospasm or the possibility of seizures. The patient's blood pressure will be monitored and controlled through medication to prevent further bleeding.

Rehabilitation – the most important part of the patient's recovery

The patients who have experienced a brain hemorrhage also often receive cognitive, occupational and physical therapy to cope with any neurological and physical deficits caused by the hemorrhage. For the patients who have unfortunately suffered significant weakness or mental and cognitive damages, rehabilitation is lengthy and requires often 6 months to one year of intense recuperation period. The rehabilitation period is often long and family members have to be patient and understanding. Family support services are of critical importance.


Aneurysms may grow without treatment but their growth rate is very slow. Aneurysm growth may be monitored on a yearly basis using CT angiography. The aneurysms that have been treated through endovascular techniques using platinum coils need to be monitored closely as the coils may compact in the aneurysm and the aneurysm may start growing, putting the patient at the risk of hemorrhage. Such patients may need to undergo angiography yearly.

The patients who have undergone surgery for aneurysm clipping have a low risk of aneurysm recurrence. These patients, however, need to be monitored as well potentially every 2-5 years. The plan for future monitoring of a treated aneurysm should be based on each patient’s aneurysm, age, and treatment rendered. Please consult with your surgeon in this regard.


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