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Intracranial Aneurysms

What are aneurysms?


A brain aneurysm is a protruding bubble or sac on a blood vessel caused by a weak spot in the vessel wall that balloons out over time. Aneurysms have thin, weak walls and have a tendency to rupture causing hemorrhage into and around vital brain structures.

How common are aneurysms?

The actual incidence is difficult to estimate since not all aneurysms present to medical attention. Autopsy studies suggest that approximately 5% of the population harbour intracranial aneurysms.

What causes aneurysms?

Factors that doctors and researchers believe contribute to the formation of brain aneurysms:

  • Smoking
  • Traumatic Head Injury
  • Use of Alcohol
  • Use of Oral Contraceptives
  • Family History of Brain Aneurysms
  • Other Inherited Disorders: Ehler's Syndrome, Polycystic Kidney Disease, and Marfan's Syndrome

How do patients with aneurysms present to the doctor?

The most frequent presentation of aneurysms is following rupture. Rupture of an aneurysm most commonly produces subarachnoid hemorrhage, which may be accompanied, by an intracerebral hemorrhage in 20-40%, intraventricular hemorrhage in 15-35% and subdural blood in 2-5%.

Other aneurysms may present by mass effect. Mass effect can come about with giant aneurysms that compress the surrounding brain, or smaller aneurysms that compress vital or sensitive structures such as cranial nerves which control eye lid opening, pupil constriction and eye movements.

Patients may also present with small strokes, seizures, or the aneurysm may be found incidentally (by chance) during brain imaging for an unrelated reason.


Although people with unruptured brain aneurysms may have headaches, this is often not associated with the actual aneurysm. Most people with unruptured brain aneurysms are completely asymptomatic have no symptoms, while others may experience some or all of the following symptoms, which suggest an aneurysm:

  • Cranial Nerve Palsy
  • Dilated Pupils
  • Double Vision
  • Pain Above and Behind Eye
  • Localized Headache

People who suffer a ruptured brain aneurysm (subarachnoid hemorrhage) will often have warning signs. The following warning signs precede about 40% of major ruptures:

  • Localized Headache
  • Nausea & Vomiting
  • Stiff Neck
  • Blurred or Double Vision
  • Sensitivity to Light (photophobia)
  • Loss of Sensation

How are aneurysms diagnosed?

An aneurysm is often diagnosed using a variety of imaging equipment. Whether someone was brought to the hospital unconscious from a rupture or is waiting to undergo treatment for an unruptured aneurysm, similar detection methods are used to pinpoint the location, size, type, and any other characteristics of the aneurysm that will help the doctors make the best decisions about how to move forward.

CT Scan (Computed Tomography)
This scan takes a picture of your brain. It is a fast and painless test, which requires you to lie on your back, very still, while you are pushed into a large, tubular machine that creates the images. This test shows whether any blood has leaked around or into the brain.

CTA (Computed Tomographic Angiography)
In some cases, doctors may choose to do a CT angiography. This test combines a regular CT scan with a contrast dye injected into a vein. Once the dye is injected into a vein, it travels to the brain arteries, and images are created using a CT scan. These images are more enhanced, because it will show exactly how fluid (blood or dye) is flowing into your brain arteries, alerting doctors to a potential aneurysm or rupture.

MRI (Magnetic Resonance Imaging)
An MRI is a safe, painless diagnostic scan that examines various areas of your body, in this case, your head. Through the use of a large doughnut-shaped magnet and a computer, magnetic signals are seen through a computer as radio waves. The computer is able to transform these radio waves into images. An MRI helps locate the aneurysm.

MRA (Magnetic Resonance Angiography)
This scan combines a regular MRI with the contrast dye, which is injected into a major vein. Like the CTA, this dye travels to the brain arteries, and images are created using an MRI. This creates a more enhanced image.

Angiogram (Arteriogram)
This test allows doctors to see the size, shape, and location of the aneurysm, as well as reveal any bleeding or vasospasm. A small incision is made on one side, or both sides, of your groin after it is locally numbed and prepped. Then, a thin tube (catheter) is threaded through arteries from the groin to the neck. A contrast dye is injected and travels to the brain arteries, X-rays are taken, showing all your arteries and any abnormalities, such as an aneurysm. There are risks involved, which will be explained to you and/or your family prior to the procedure.

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