More About Brain Aneurysms

A cerebral aneurysm (also called an intracranial aneurysm or brain aneurysm) is a bulging, weakened area in the wall of an artery in the brain, resulting in an abnormal ballooning of the artery that is at risk for rupturing. A cerebral aneurysm more often happens in an artery located in the front part of the brain that supplies oxygen-rich blood to the brain tissue. Arteries anywhere in the brain can develop aneurysms. A normal artery wall is made up of 3 layers. The wall where the aneurysm forms is thin and weak because of an abnormal loss or absence of the muscular layer of the artery wall, leaving only 2 layers. There are several types of aneurysms:

  • Berry aneurysm. The most common type of cerebral aneurysm is called a saccular, or berry, aneurysm, happening in 90% of cerebral aneurysms. This type of aneurysm looks like a "berry" with a narrow stem. More than one aneurysm may be present.
  • Fusiform aneurysm. A fusiform aneurysm bulges out on all sides. This forms a dilated artery. Fusiform aneurysms are often associated with atherosclerosis.
  • Dissecting aneurysm. A dissecting aneurysm results from a tear along the length of the artery in the inner layer of the artery wall, causing blood to leak in between the layers of the wall. This may cause a ballooning out on one side of the artery wall, or it may block off or obstruct blood flow through the artery. Dissecting aneurysms usually happen from traumatic injury, but they can also happen spontaneously. The shape and location of the aneurysm may determine which treatment is recommended.


Most cerebral aneurysms present without any symptoms and are small in size (less than 10 millimeters, or less than four-tenths of an inch, in diameter). Smaller aneurysms may have a lower risk of rupture.

Currently, the cause of cerebral aneurysms is not clearly understood. Brain aneurysms are associated with several factors. This includes smoking, high blood pressure, and family history (genetic). The ultimate cause of a brain aneurysm is an abnormal breaking down and weakening in the wall of an artery, and the effects of pressure from the pulsations of blood being pumped forward through the arteries in the brain. Certain locations of an aneurysm may create greater pressure on the aneurysm, such as the area where the artery divides into smaller branches.

  • A cerebral aneurysm (also called an intracranial aneurysm or brain aneurysm) is a bulging, weakened area in the wall of an artery in the brain. This results in an abnormal widening, ballooning, or bleb.
  • Because there is a weakened spot in the aneurysm wall, there is a risk for rupture (bursting) of the aneurysm.
  • You should seek medical attention immediately if you are experiencing some or all of these symptoms:
    • Sudden severe headache or "the worst headache of your life”
    • Loss of consciousness
    • Nausea and/or vomiting
    • Stiff neck
    • Sudden blurred or double vision
    • Sudden pain above or behind the eye or trouble seeing
    • Sudden change in mental status or awareness
    • Sudden trouble walking or dizziness
    • Sudden weakness and numbness
    • Sensitivity to light known as photophobia
    • Seizure activity
    • Drooping eyelid