Types of Brain Aneurysms

A brain aneurysm, also known as a cerebral or intracranial aneurysm, is a weak spot on an artery in the brain that balloons out, forming a sac-like structure. The most frightening complication is rupture, which can lead to life-threatening bleeding into the surrounding area in a condition called subarachnoid hemorrhage. Unruptured brain aneurysms are relatively common, and is estimated to affect around 3 – 5% of the general population.

Brain aneurysms are often categorized into 5 types: 

Saccular aneurysm, also known as berry aneurysm, is the most common type of brain aneurysm and account for 80 – 90% of cases. They appear as a rounded sac or pouch-like protrusion that bulges out from the side of an artery wall and typically develop at arterial bifurcations, where arteries branch off into smaller vessels.

A fusiform aneurysm is a type of brain aneurysm that appears as an area of dilation or widening of a blood vessel in a uniform, spindle-shaped manner along a certain segment. Unlike saccular aneurysms, which protrude from the arterial wall in a pouch-like structure, fusiform aneurysms involve a more diffuse enlargement of the vessel. 

Fusiform aneurysms have a relatively lower likelihood of rupturing when compared with saccular aneurysms, but they can still cause symptoms and other complications such as thrombosis (formation of blood clots within the aneurysm), embolic stroke (traveling of blood clots to other parts of the brain causing blockage of blood supply), or compression of adjacent structures if they enlarge significantly. 

A pseudoaneurysm, also known as a false aneurysm, is a localized collection of blood that forms outside of the wall of an artery or vein. Unlike a true aneurysm, where the vessel wall itself is weakened and bulges out, a pseudoaneurysm typically occurs due to trauma or injury to the blood vessel wall, leading to a leakage of blood that collects and forms a sac-like structure.

Pseudoaneurysms can develop after procedures such as arterial punctures via catheterizations or injections. They can also result from trauma, such as blunt force injuries or penetrating wounds that damage blood vessels. Intracranial pseudoaneurysms are rare, and account for about 1% of all intracranial aneurysms.

A mycotic aneurysm is a rare type of aneurysm that develops as a result of an infection in the arterial wall. Most are associated with infections in other parts of the body or bacteria in the bloodstream. Infection of the heart valves (bacterial endocarditis) in particular has been associated with numerous cases of mycotic aneurysm.

Blister aneurysms usually develop on the internal carotid artery, but they can affect any of the brain’s blood vessels. They get their name from their blister-like appearance, where the neck is wider than the dome. Blister aneurysms have a high likelihood of bleeding and are associated with a higher mortality rate. 

Brain aneurysms are associated with many potential causes and risk factors, some acquired and others hereditary. Some of the modifiable risk factors for brain aneurysms include: 

• High blood pressure (hypertension)
• Excess alcohol consumption 
• Cigarette smoking 
• Illicit drug use, especially cocaine and methamphetamine 
• Traumatic head injuries 
• Infections 

Some of the non-modifiable causes of and risk factors for brain aneurysms include: 

• Age: Brain aneurysms are more common from ages 40 to 60 
• Gender: Females have a higher likelihood of developing cerebral aneurysms 
• Medical conditions: The following are associated with the development of brain aneurysms:
  • Tuberous sclerosis
  • Fibromuscular dysplasia 
  • Noonan’s syndrome 
  • Hereditary hemorrhagic telangiectasia 
  • Polycystic kidney disease 
  • Alpha-glucosidase deficiency 
  • Coarctation of the aorta 
  • Alpha 1-antitrypsin deficiency 
  • Arteriovenous malformation 
  • Ehlers–Danlos syndrome 
  • Klinefelter syndrome 

Individuals with a family history of brain aneurysms have a higher likelihood of developing the condition compared to the general population. If you are concerned about your increased risk due to family history, speak to your primary care doctor for further guidance and evaluation. 

Although most brain aneurysms do not cause symptoms, they can be a cause for concern due to their potential for life-threatening rupture. Some of the risk factors associated with an increased likelihood of aneurysm rupture include:

• Ethnicity: While those of European and American descent are at a lower risk, those of Finnish and Japanese descent have a much higher risk of an aneurysm rupturing.
• High blood pressure: Uncontrolled high blood pressure can further stress the walls of the blood vessels, increasing the chances of rupture.
• Age: Those older than 70 are at a higher risk of aneurysmal rupture.
• Size of the aneurysm: Aneurysms larger than 7mm are more prone to rupture, and the risk increases with increasing size of the aneurysm.
• Earlier aneurysm rupture: History of a different aneurysm rupturing indicates a higher risk of the current aneurysm rupturing.
• Location of the aneurysm: Aneurysms arising from the internal carotid artery are at a lower risk of rupturing, while those arising from the middle cerebral arteries, posterior cerebral arteries, and basilar arteries are at a higher risk of rupture.

Most brain aneurysms are painless and usually don’t cause symptoms. However, symptoms can occur if the aneurysm is large and compresses nearby nerves. They also cause more serious symptoms and become potentially fatal when they rupture and bleed. 

• Symptoms of an intact (unruptured) brain aneurysm may include: 
• Blurred or impaired vision, leading to frequent squinting
• Dilated (enlarged) pupils
• Drooping of an eyelid

Some of the symptoms of a ruptured and bleeding brain aneurysm include: 

• Severe headache, often described as the worst headache of one’s life
• Stiff neck 
• Nausea and vomiting 
• Drowsiness
• Lack of coordination 
• Neck pain
• Slurred speech 
• Rapid onset of headaches
• Confusion
• Loss of consciousness (coma)

Symptoms of brain aneurysms can be easy to mistake for other health issues, such as a bad headache after a hard day at work. However, symptoms of a ruptured aneurysm are usually more serious. Seek immediate medical attention if you experience symptoms of a ruptured brain aneurysm, such as a severe headache associated with vomiting and confusion.

Brain aneurysms come in various sizes, but usually range from one-eighth of an inch to 1 inch in diameter. Size matters because it can influence the severity of symptoms and likelihood of rupture. Larger aneurysms are more likely to rupture.

Generally doctors recommend treatment for aneurysms larger than 7 millimeters in diameter (about 1/4 of an inch) because they have a higher likelihood of rupturing. Certain characteristics of smaller aneurysms may also warrant treatment, such as a history of rupture, location on the basilar or posterior cerebral artery, or the presence of irregularities on the aneurysm wall, also known as “daughter sacs”.

Depending on the aneurysm’s size, location, and other crucial factors, your doctor may recommend various treatment options. Common treatment options include the following: 

• Microsurgical clipping 
• Artery occlusion and bypass 
• Endovascular coiling 
• Flow diverting stent placement 

In some cases, your doctor may recommend observation for small and asymptomatic brain aneurysms, especially if the risks associated with treatment outweigh the potential benefits. Fortunately, advancements in medical technology and treatment options have significantly improved outcomes for patients with brain aneurysms.

Even ruptured aneurysms, once considered dire emergencies, are now treatable, with patients undergoing treatment for ruptured aneurysms having a 60% survival rate. Early detection, careful monitoring, and appropriate treatment decisions can greatly improve the prognosis for individuals with brain aneurysms, offering hope and a chance for a better quality of life.

• Brain aneurysms are blood-filled balloons that form on weak points in the blood vessels of the brain.
• Most brain aneurysms do not cause symptoms, but when they do, vision impairments are the most common.
• A ruptured brain aneurysm is a life-threatening emergency that requires prompt medical attention.
• Consult a doctor if you are concerned about an increased risk of brain aneurysms due to your family history or other medical conditions.

• National Institute of Neurological Disorders and Stroke
• American Association of Neurological Surgeons (AANS): Cerebrovascular Disease
• Brain Aneurysm Foundation
• American Association of Neurological Surgeons (AANS): Cerebral Aneurysm
• American Brain Foundation (ABF)