Brain aneurysm, known also as intracranial or cerebral aneurysm, is a protruding bubble or sac on a weak area of a brain artery. Aneurysms balloon out over time and have a tendency to rupture causing blood to leak (hemorrhage) into and around vital brain structures.

A large cerebral aneurysm at the junction of the right internal carotid and anterior cerebral arteries.


The cause of aneurysm formation is open to debate. However, brain aneurysm may result from a small area of weakness or thinning near a branch point of the blood vessel, most commonly at the base of the brain.


A number of factors may increase the risk of aneurysm formation, including:

  • Family history
  • Atherosclerosis
  • Inherited genetic traits for conditions such as polycystic kidney disease, Ehlers-Danlos syndrome, Marfan syndrome, neurofibromatosis
  • Previous aneurysm
  • Traumatic head injury

The main risk of an aneurysm is rupture and subarachnoid hemorrhage (SAH). Factors that increase the risk of rupture are:

  • Age
  • High blood pressure
  • Alcohol and drug abuse (especially cocaine)
  • Cigarette smoking
  • Size, shape and location of the aneurysm


Brain aneurysms most frequently present for medical attention because they bleed, causing vague, non-specific symptoms such as headaches, visual problems, slowed mental processes, balance problems, etc. The majority of aneurysms that rupture do so without any preliminary signs or symptoms. Some effects that occur upon rupture are:

  • Onset of a "thunderclap" (sudden, extremely painful) headache
  • Stiff neck
  • Intolerance of bright light
  • Nausea and/or vomiting
  • Seizures
  • Sudden weakness
  • Loss of consciousness

If you experience a sudden and severe headache, seek immediate medical attention, as it possibly may signal SAH as the cause.

In about 20 percent of aneurysms that go on to rupture, a "warning leak" occurs several days before subarachnoid hemorrhage. In these patients, the warning headache may be much milder than the thunderclap. Small strokes or seizures also may occur.

Unruptured aneurysms can press on adjacent brain structures such as cranial nerves and cause symptoms such as cranial nerve palsy, dilated pupils, double vision and pain above and behind the eye.


The advent of safe, noninvasive imaging techniques such as magnetic resonance imaging (MRI) and angiography (MRA) recently has led to an increasing number of unruptured brain aneurysms being discovered in patients who do not display symptoms (asymptomatic).

Typically, clinicians use these scans to evaluate unrelated conditions such as mild headaches, vertigo, sinusitis, head trauma. This incidental, early detection of an unruptured aneurysm may help guide treatment decisions by offering physicians the opportunity to diagnose, intervene, and manage the condition sooner.

Other procedures used in the diagnosis of brain aneurysms include:

  • Computed Tomography Angiography (CTA), a minimally invasive imaging procedure also useful in detecting unruptured aneurysms
  • Computed Tomography (CT) scan, which is most useful in larger subarachnoid hemorrhages and when done within 24 hours of the bleed
  • Lumbar puncture, or spinal tap, to detect blood in the spinal fluid
  • Cerebral angiogram


Aneurysms that have ruptured require treatment to prevent rebleeding. Following the initial rupture of an aneurysm, rebleeding is very common, especially within the first two weeks after rupture, and is usually more severe than the initial rupture. The two treatment options are:

  • Surgical clipping of the aneurysm
  • Endovascular coiling: this procedure involves the insertion of platinum coils through a microcatheter into the aneurysm. These coils form a ball that excludes the aneurysm from the normal vessel. Occasionally a small flexible stent is placed in the vessel to hold the coils in the aneurysm.

    Endovascular coiling of an aneurysm

An experienced cerebrovascular neurosurgeon and an interventional neuroradiologist should review each patient's aneurysm to offer the most appropriate treatment for the patient's specific condition.

In contrast to managing a ruptured aneurysm, factors that complicate the decision whether to treat or monitor an unruptured aneurysm broadly divide into those affecting the "natural history" (the likelihood of rupture of the aneurysm) and those concerning the risks of treatment.

Influences on the natural history include patient factors such as:

  • Age
  • Sex
  • Preexisting medical conditions

Aneurysm characteristics also influence the natural history:

  • Size
  • Location
  • Shape
  • Presence of symptoms

The experience of the surgical team and the treating hospital are important factors in treatment risk.


There is no known method to prevent the formation of aneurysms. The risk of rupture can be somewhat modified by:

  • Blood pressure control
  • Cessation of smoking
  • Cessation of drug abuse
  • Surgical or endovascular treatment

To learn more about Brain aneurysms and their treatment call the Mount Sinai Department of Neurosurgery at 212-241-2377.

By the Mount Sinai Department of Neurosurgery

Graphic of coiling procedure used with permission from Boston Scientific.