Brain Aneurysm: Causes And Symptoms

Overview 

What is a brain aneurysm?

A brain aneurysm, also known as a cerebral or intracranial aneurysm, is a weakened area in the wall of a blood vessel inside the brain. As blood flows through the blood vessels in the brain, it can put pressure on the weakened area of the blood vessel where an aneurysm is present.  This pressure can cause a bulge or ballooning of a blood vessel and expand over time. The expansion of the aneurysm can make it more prone to rupture (burst), especially if the walls of the blood vessel become thinner and weaker.¹

Brain aneurysms can occur anywhere in the brain but are most commonly found in the major arteries at the base of the brain, particularly in areas where the blood vessels branch off.  Approximately 2-3% of people in the UK have had a brain aneurysm which is typically more common in women than men. Most brain aneurysms do not cause symptoms and are discovered during tests for other conditions, serious consequences can arise if an aneurysm ruptures, leading to bleeding to the brain, which can be serious and require immediate medical attention.¹

Different types of brain aneurysms 

Brain aneurysms can be classified into different types based on their shape, location, and how they develop.

Different types of brain aneurysms can include:

• Saccular aneurysms: 

Saccular aneurysms, also known as berry aneurysms, are a small, pouch-like bulge that forms on the wall of a blood vessel in the brain. It is the most common type of aneurysm and typically develops at branching points of the major arteries in the brain. It resembles a small berry attached to the blood vessel. They are the most common type of brain aneurysm and can vary in size and location within the brain.²

• Fusiform aneurysms: 

Fusiform aneurysms are another type of brain aneurysms. Instead of having a small pouch-like bulge, they are elongated and spindle-shaped. These aneurysms involve only one side of the or the entire circumference of the blood vessel and are less common compared to saccular aneurysms.³  

• Mycotic aneurysms: 

Mycotic aneurysms is a rare type of brain aneurysm that is caused either by a bacterial or fungal infection. Unlike other types of aneurysms that develop due to a weak wall of a blood vessel, mycotic aneurysms result directly from the invasion of pathogens into the walls of blood vessels. These types of aneurysms are seen in people with conditions such as endocarditis or a weakened immune system.⁴

Brain aneurysm sizes

Brain aneurysms can also vary in size, ranging from small to large. The size of an aneurysm can impact its risk of rupture and the potential severity of the resulting complications.  

• Small aneurysms: small aneurysms are typically less than 11 millimetres (mm) in diameter. While small aneurysms are less likely to rupture compared to larger ones, they can still pose a risk, especially if other risk factors are present.⁵ 
• Medium aneurysms: medium-sized aneurysms are between 5 to 11 millimetres (mm) in diameter. These aneurysms have a higher risk of rupture compared to smaller ones but they may still remain stable for years without causing symptoms.⁵ 
• Large aneurysms: large aneurysms are between 11-24 millimetres (mm) in diameter.  These aneurysms have a significantly higher risk of rupture and are more likely to cause symptoms such as headaches, visual disturbance, or neurological deficits due to their size and the pressure on surrounding brain structures.⁵
• Giant aneurysms: giant aneurysms are defined as aneurysms larger than 25 millimetres (mm) in diameter. These aneurysms are rare but are associated with a higher risk of rupture and severe complications, including the mass effect on nearby brain structures, thrombosis (clot formation) within the aneurysm, or compression of cranial nerves.⁵

Symptoms 

Symptoms of a brain aneurysm can vary depending on whether the aneurysm is ruptured or has ruptured.  

Unruptured aneurysm 

Most people with an unruptured aneurysm will have little or no symptoms, especially if the aneurysm is small. An unruptured aneurysm would cause symptoms if they are large and they put pressure on tissue or nerves inside the brain.¹

Symptoms of an unruptured brain aneurysm may include:

• Pain above and behind the eye 
• Numbness or weakness on one side of the face
• Visual changes, such as loss or double vision 
• A dilated pupil in the eye
• Loss of balance 
• Difficulty speaking
• Difficulty with concentrating or problems with short-term memory  

Ruptured aneurysm 

Ruptured brain aneurysms can lead to severe complications such as subarachnoid haemorrhage, hydrocephalus, cerebral vasospasm, rebleeding, ischemic stroke, neurological deficits, seizures, cognitive and behavioural changes. When an aneurysm ruptures, symptoms suddenly begin with an extremely severe headache. Other symptoms of a ruptured brain aneurysm will also come suddenly and may include:¹

• Nausea 
• Vomiting 
• Double vision 
• Stiff neck or neck pain 
• Sensitivity to light 
• Seizures
• Weakness on one side of the body or in any limbs 
• Loss of consciousness 

Causes 

Brain aneurysms develop when the walls of the major arteries in the brain become thin and weak. Brain aneurysms occur at points where the arteries divide and branch off as these sections are the weakest. 

Inherited risk factors for developing a brain aneurysm 

Sometimes a brain aneurysm can form due to genetic risk factors. Having a close relative, such as a parent or sibling who has had a brain aneurysm can increase a person’s risk of developing a brain aneurysm as well.¹

Additionally, some medical conditions have been associated with an increased risk of developing brain aneurysms. 

These conditions can include:

• Autosomal dominant polycystic kidney disease: this genetic condition causes cysts to form in the kidneys as well as affecting blood vessels throughout the body, including the brain. High blood pressure can weaken the wall of blood vessels, making them prone to developing a brain aneurysm.⁶ 
• Neurofibromatosis type 1: this genetic condition causes skin colour changes and tumours to grow along nerves throughout the body, including the brain. Having this condition can lead to vascular abnormalities, leading to the development of brain aneurysm.⁷   
• Marfan syndrome: this genetic condition affects the connective tissue have a higher risk of developing weakness in the walls of blood vessels throughout which can lead to the development of an aneurysm.⁸
• Ehlers-Danlos syndrome: this genetic condition also affects the connective tissue and is associated with an increased risk of vascular complications throughout the body and brain, which can cause brain aneurysm.⁹ 

Other risk factors for developing a brain aneurysm 

There are several other factors that can increase a person’s risk of developing a brain aneurysm.  

These other factors can include:⁵

• Smoking: cigarette smoking has been linked to developing a brain aneurysm. This is because smoking can damage the arteries and increase blood pressure, making the walls of the arteries weaker. Smoking can also cause changes in blood flow and promote the build-up of fatty deposits in the arteries (atherosclerosis) which can further increase the risk.¹⁰ 
• Hypertension: hypertension (high blood pressure) is when the force of blood pushing against the walls of the arteries is consistently high. This increased pressure can increase the person’s risk of developing a brain aneurysm and can also cause atherosclerosis and changes in blood flow patterns.¹¹ 
• Age: While brain aneurysms can occur at any age, they are more likely to develop with older age, especially in those over the age of 40. This may be due to age-related changes in blood vessel structure and function and exposure to other risk factors (e.g., smoking or alcohol use) over time.¹²
• Gender: people assigned female at birth are more likely to develop brain aneurysms compared to men. This gender difference may be because of hormonal factors, such as a decrease in oestrogen during menopause or other life events such as pregnancy or childbirth.^13,14 
• Drug abuse: stimulants such as cocaine or amphetamines can increase a person’s risk of developing a brain aneurysm. This is because these drugs can raise blood pressure and narrow blood vessels. This puts extra stress on the walls of blood vessels in the brain, making them more prone to damage and leading to the formation of aneurysms.  Also, drug use can increase the risk of head injury which can also contribute to the development of brain aneurysms.¹⁵ 

Summary 

In summary, a brain aneurysm is a weakened area in the wall of a blood vessel inside the brain.  Blood flowing through these vessels can exert pressure on the weakened area, leading to a bulge or ballooning of the blood vessel over time.  While brain aneurysms can occur anywhere in the brain, they are most commonly found in the major arteries at the base of the brain. Brain aneurysms can be classified into different types based on their shape, location, and how they develop. Additionally, they can vary in size, ranging from small to giant aneurysms, with larger aneurysms posing a higher risk of rupture. Symptoms of a brain aneurysm can vary depending on whether the aneurysm is ruptured or unruptured. Ruptured brain aneurysms can lead to severe complications such as subarachnoid haemorrhage or hydrocephalus, among others. Several inherited and non-inherited risk factors such as genetic conditions, smoking, hypertension, age, gender, and drug abuse, can increase the risk of developing a brain aneurysm.