Aneurysm growth is not always predictable. Growth can increase the risk of rupture and bleeding into the brain, which can be life threatening. Because of this, people should work with a doctor to monitor aneurysms.

A brain aneurysm, also known as a cerebral aneurysm, is an abnormal and weakened area in the wall of a blood vessel within the brain. It resembles a balloon or bulge in the blood vessel.

This article looks at how brain aneurysms grow, signs of an aneurysm, and when to speak with a doctor.

A person with a brain aneurysm reading something on a screen that's reflected in their glasses.-1Share on Pinterest

Brain aneurysms do not always grow at a predictable rate. Smaller aneurysms may grow more slowly or may remain stable over time, while larger aneurysms may grow more rapidly. However, there can be exceptions, and size does not determine growth rate.

Aneurysms at arterial bifurcations (branching points) in the brain may be more prone to growth due to the force of the blood flow, but this is not a rule that applies to all cases.

Doctors categorize brain aneurysms by the following sizes, with larger aneurysms being more likely to cause worsening symptoms or rupture.

  • Small: Less than 11 millimeters (mm) in diameter, which is roughly the same size as a large pencil eraser.
  • Large: Between 11–25 mm in diameter, which is approximately the diameter of a dime.
  • Giant: More than 25 mm across, which is larger than a quarter.

Monitoring growth

Doctors use medical imaging techniques, such as magnetic resonance angiography or computed tomography angiography, to monitor aneurysms over time.

The frequency of monitoring depends on factors including the size, location, and stability of the aneurysm. Stable aneurysms may require less frequent monitoring, while larger or unstable ones may need more frequent assessment.

Complications of a ruptured brain aneurysm can include:

  • Subarachnoid hemorrhage (SAH): This is the primary complication of a ruptured brain aneurysm. It occurs when blood leaks into the space between the brain and the thin tissues that cover it, called the subarachnoid space.
  • Vasospasm: Following an SAH, blood vessels in the brain may constrict and narrow, reducing blood flow.
  • Cerebral edema: Swelling of brain tissue can occur due to irritation caused by blood in the subarachnoid space.
  • Stroke: Brain damage from an interruption of blood supply in one or more areas of the brain can occur due to disruption of blood flow after an aneurysm rupture.

Learn about the potential causes of a ruptured brain aneurysm.

Whether or not an aneurysm grows over time can vary from person to person and even among different aneurysms within the same individual.

Given the unpredictable nature of aneurysm growth, doctors carefully assess the characteristics of each aneurysm and tailor monitoring and treatment plans to the person.

Sometimes, a doctor may surgically treat an unruptured brain aneurysm to help prevent rupturing. However, sometimes doctors will continue to observe aneurysms instead of surgically treating them.

Doctors do not know exactly what causes a brain aneurysm to form. Aneurysms typically begin with weakening in the walls of an artery in the brain. Several factors can increase the risk of this occurring, including:

The risk of developing an aneurysm may also increase with age, with most aneurysms occurring in people over 40 years old.

Learn how to help prevent a brain aneurysm.

Most unruptured brain aneurysms do not cause any noticeable symptoms. Healthcare professionals may discover them incidentally during medical imaging for unrelated issues.

Ruptured brain aneurysms are a medical emergency and typically cause many symptoms.

Unruptured brain aneurysms

In some cases, unruptured aneurysms may produce mild or intermittent symptoms due to pressure on nearby areas in the brain. These symptoms can include:

Ruptured brain aneurysm

A ruptured brain aneurysm is a medical emergency and can result in SAH, which is bleeding into the space surrounding the brain.

The main symptom of a ruptured aneurysm is a severe “thunderclap” headache that comes on suddenly. Some describe this experience as the worst headache they have ever experienced.

Other signs and symptoms of a ruptured brain aneurysm can include:

People should seek immediate medical help if they or someone else experiences these symptoms.

If someone thinks they are at risk of a brain aneurysm, they should speak with a doctor. A doctor can assess a person’s risk and recommend appropriate monitoring or screening.

People should seek immediate emergency help if they or someone else experiences any of the symptoms of a ruptured brain aneurysm. This includes the following:

  • a severe “thunderclap” headache
  • loss of consciousness
  • nausea and vomiting
  • vision changes
  • seizure
  • an altered mental state, including confusion

Aneurysms can vary in size and shape and may or may not grow over time. The growth rate of an aneurysm is unpredictable and varies among individuals.

Regular monitoring with medical imaging is essential to track aneurysm growth.

Small or unruptured aneurysms may be asymptomatic. However, a ruptured aneurysm is a medical emergency that requires prompt treatment.