An aneurysm occurs when the walls of blood vessels are weakened, causing a blood-filled bulge. Left untreated, an aneurysm may rupture, resulting in hemorrhage or even death. Aneurysms most often occur at the base of the brain or near the heart.

Brain aneurysms are weak artery walls in the brain that bulge, and they may rupture or burst. 2 to 5 percent of people in the United States develop them. Aneurysms look like berries attached to the artery by a “neck.” They have several forms, as shown in the illustration below.

Aneurysm forms 'berries' attached to an artery.

The signs of a brain aneurysm vary person to person, depending on how the size of the aneurysm, how fast it grows, and the location in the brain.


Most people with an unruptured brain aneurysm show no signs or symptoms. Others may have symptoms because the aneurysm presses on the brain or nerves. The signs of aneurysm include:

  • numbness
  • weakness or paralysis of the face, arm or leg
  • a drooping eyelid
  • a dilated (enlarged) pupil
  • decreased vision or double vision
  • pain above and behind the eye
  • localized headache
  • seizure

Signs of Ruptured Aneurysms

When a brain aneurysm bursts, it usually causes internal bleeding between the skull and the brain. This is called a subarachnoid hemorrhage. A ruptured aneurysm often causes a sudden, severe headache that some patients describe as “the worst headache of my life.”

When an aneurysm hemorrhages, symptoms can look similar to stroke symptoms of numbness, weakness, and difficulty speaking. Other possible signs of aneurysm are:

  • nausea and vomiting
  • stiff neck
  • double vision
  • and/or loss of consciousness

If you experience any of these symptoms, call 9-1-1 immediately.

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