Cerebrovascular Neurosurgery - Intercranial Aneurysm
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. Given their thin, fragile walls, aneurysms 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 harbours intracranial aneurysms.

What causes aneurysms?

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

  • 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?

Aneurysms most frequently present after rupture. Rupture of an aneurysm usually produces subarachnoid hemorrhage, which may be accompanied by an intracerebral hemorrhage in 20-40% of cases, intraventricular hemorrhage in 15-35% of cases, and subdural blood in 2-5% of cases.

Other aneurysms may present before rupture by the effects of pressure exerted by their mass. This mass effect can result from giant aneurysms that compress the surrounding brain, or from 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 or seizures, or an aneurysm may be found incidentally during brain imaging for an unrelated reason.


Although people with unruptured brain aneurysms may have headaches, this is not often associated with the actual aneurysm. Most people with unruptured brain aneurysms are completely asymptomatic; others may experience some or all of the following symptoms:

  • 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 and vomiting
  • stiff neck
  • blurred or double vision
  • sensitivity to light (photophobia)
  • loss of sensation
How are aneurysms diagnosed?

Generally it is imaging equipment that facilitates the diagnosis of an aneurysm. Whether a patient is waiting to undergo treatment for an unruptured aneurysm or is brought to the hospital unconscious from a ruptured aneurysm, the same detection methods are used to pinpoint the location, size, type, and any other characteristics of the aneurysm which will help the doctors best decide how to move forward.

CT Scan (Computed Tomography)
This scan takes a picture of the brain. It is a fast and painless test, which requires one to lie on his or her back, very still, while being pushed into a large, tubular machine that creates the images. This test shows whether any blood has leaked into or around 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 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 enhanced images show exactly how fluid (the blood with dye) is flowing into the brain arteries, alerting doctors to a ruptured aneurysm or a potential rupture.

MRI (Magnetic Resonance Imaging)
An MRI is a safe, painless diagnostic scan that examines various areas of the body, and in this case, the head. A large doughnut-shaped magnet, radio waves, and a computer are used to generate images that help locate the aneurysm.

MRA (Magnetic Resonance Angiography)
This scan combines a regular MRI with contrast dye which is injected into a major vein. As with the CTA, this dye travels to the brain arteries and allows the creation of enhanced MRI images.

Angiogram (Arteriogram)
This test allows doctors to see the size, shape, and location of the aneurysm, as well as revealing any bleeding or vasospasms. A small incision is made on one or both sides of the groin, after it is locally numbed and prepped. A catheter is then threaded from the groin through the arteries to the neck. An injected contrast dye travels to the brain arteries and X-rays are taken, showing all the arteries and any abnormalities, such as an aneurysm. The risks of this procedure are explained to the patient and/or the family prior to the procedure.