Cerebral Aneurysm

What is a Cerebral Aneurysm?

A cerebral aneurysm (also called a brain aneurysm or intracranial aneurysm) is a weak, bulging spot on the wall of a brain artery. Think of it like a weak spot on a garden hose that balloons outward under water pressure.

Most aneurysms develop where arteries branch or fork, because these junctions experience the most stress from blood flow. They can range from a few millimeters (the size of a small berry) to over 25mm (larger than a grape).

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Imaging Appearance on MRI

Standard MRI Sequences

On MRI, an unruptured aneurysm typically appears as:

• Flow void: A dark, round or lobulated structure on standard sequences due to rapidly flowing blood
• Well-defined margins: Clear borders distinguishing it from surrounding brain tissue
• Location at vessel branch points: Most commonly at arterial bifurcations

MR Angiography (MRA)

• Bright signal: Aneurysm appears bright white on MRA sequences
• Neck and dome visible: Can often distinguish the narrow neck from the wider dome
• 3D reconstruction: Allows detailed visualization of size, shape, and relationship to parent vessels

Key Features Radiologists Assess

1. Size: Measured in millimeters (small ＜7mm, large 7-25mm, giant ＞25mm)
2. Shape: Regular vs. irregular (irregular = higher rupture risk)
3. Location: Anterior vs. posterior circulation
4. Neck width: Wide neck vs. narrow neck affects treatment options
5. Daughter sacs: Small blebs increase rupture risk

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Types of Cerebral Aneurysms

1. Saccular Aneurysm (Most Common - 90%)

• Appearance: Round berry-like bulge with a neck
• Also called: "Berry aneurysm"
• Rupture risk: Moderate, depends on size and location

2. Fusiform Aneurysm

• Appearance: Spindle-shaped dilation of entire arterial segment
• Characteristics: No distinct neck, involves entire vessel circumference
• Rupture risk: Generally lower than saccular

3. Mycotic Aneurysm

• Cause: Infection weakening vessel wall
• Characteristics: Irregular shape, often multiple
• Rupture risk: High due to inflammatory damage

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Common Locations

Anterior Circulation (85%)

1. Anterior communicating artery (ACoA): 30-35%
2. Posterior communicating artery (PCoA): 25%
3. Middle cerebral artery (MCA) bifurcation: 20%
4. Internal carotid artery (ICA): 10%

Posterior Circulation (15%)

1. Basilar artery tip: 5-7%
2. Vertebrobasilar junction: 3-5%
3. Posterior inferior cerebellar artery (PICA): 2-3%

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Risk Factors

Non-Modifiable

• Family history: 2-3x higher risk if first-degree relative affected
• Genetic conditions: Polycystic kidney disease, Ehlers-Danlos syndrome, Marfan syndrome
• Female sex: Women have slightly higher risk
• Race: Higher in people of Finnish and Japanese descent
• Age: Risk increases with age

Modifiable

• Smoking: Single biggest modifiable risk factor
• High blood pressure: Chronic hypertension weakens vessel walls
• Heavy alcohol use: More than 3 drinks/day
• Cocaine use: Causes acute blood pressure spikes
• Oral contraceptives: Small increased risk in women

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Rupture Risk Assessment

Size-Based Risk (Annual Rupture Rate)

• ＜ 7mm: 0.1-0.5% per year
• 7-12mm: 0.5-3% per year
• 13-24mm: 3-15% per year
• ≥ 25mm (giant): 6-40% per year

High-Risk Features

• Irregular shape with blebs or daughter sacs
• Posterior circulation location (higher rupture risk)
• Symptomatic aneurysm causing symptoms before rupture
• Rapid growth on serial imaging
• Multiple aneurysms

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Symptoms and Warning Signs

Unruptured Aneurysm (Often No Symptoms)

Most people with unruptured aneurysms have no symptoms. When symptoms occur, they may include:

• Sudden severe headache (different from typical headaches)
• Vision problems: Blurred or double vision, drooping eyelid
• Facial pain or numbness
• Dilated pupil (one pupil larger than the other)
• Seizures (rare)

Ruptured Aneurysm (Medical Emergency)

Thunderclap headache: Sudden, severe "worst headache of my life"

Other symptoms:

• Stiff neck
• Nausea and vomiting
• Loss of consciousness
• Sensitivity to light
• Seizures
• Confusion or altered mental status

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Diagnostic Workup

Initial Imaging

1. CT angiography (CTA): Fast, excellent for detecting aneurysms ＞3mm
2. MR angiography (MRA): No radiation, good for screening and follow-up
3. Digital subtraction angiography (DSA): Gold standard, invasive, used for treatment planning

Additional Tests

• Genetic counseling: If family history or genetic syndrome suspected
• Cardiac evaluation: Some aneurysms associated with coarctation of aorta
• Kidney screening: For polycystic kidney disease

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Treatment Options

Observation (Watchful Waiting)

Appropriate for:

• Small aneurysms (＜7mm)
• Low-risk location
• No symptoms
• Elderly patients with other health issues

Follow-up: MRA every 1-2 years to monitor for growth

Surgical Clipping

• Procedure: Neurosurgeon places metal clip across aneurysm neck
• Advantages: Permanent, durable repair
• Requires: Craniotomy (opening skull)
• Recovery: 4-6 weeks

Endovascular Coiling

• Procedure: Catheter inserted through groin artery, platinum coils packed into aneurysm
• Advantages: Less invasive, faster recovery
• May require: Repeat treatment if aneurysm recurs
• Recovery: 1-2 weeks

Flow Diverter Stents

• Procedure: Mesh stent redirects blood flow away from aneurysm
• Best for: Large or wide-necked aneurysms
• Requires: Blood thinners for several months

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Prognosis and Follow-Up

Unruptured Aneurysm

• With treatment: ＞95% success rate for preventing rupture
• Without treatment: Risk depends on size, location, and risk factors
• Lifestyle modifications: Quit smoking, control blood pressure

After Rupture

• Overall mortality: 40-50% of ruptures are fatal
• Survivors: 30% have permanent disability, 30% recover well
• Rebleeding risk: 40% if untreated in first 4 weeks

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Living with a Brain Aneurysm

Lifestyle Modifications

• Stop smoking immediately — #1 priority
• Control blood pressure — Target ＜140/90, ideally ＜130/80
• Avoid straining: Heavy lifting, intense Valsalva maneuvers
• Limit alcohol: No more than 1-2 drinks per day
• Avoid cocaine and other stimulants
• Manage stress through relaxation techniques

Safe Activities

Most daily activities are safe:

• Light to moderate exercise (walking, swimming)
• Sexual activity (unless specifically restricted)
• Air travel
• Driving (unless experiencing symptoms)

Activities to Discuss with Doctor

• Contact sports
• Scuba diving
• High-intensity interval training
• Pregnancy planning

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Questions to Ask Your Doctor

1. What is the exact size and location of my aneurysm?
2. What is my personal rupture risk based on all my factors?
3. Should the aneurysm be treated or monitored?
4. If monitored, how often will I need follow-up scans?
5. What symptoms should prompt me to seek emergency care?
6. Are there any activity restrictions I should follow?
7. Should my family members be screened?
8. What treatment option would you recommend and why?

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Summary

A cerebral aneurysm is a bulging weak spot on a brain artery, most commonly found at vessel branch points. While the diagnosis can be frightening, most aneurysms never rupture. Treatment decisions depend on size, location, shape, and individual risk factors. Small aneurysms are often safely monitored with regular imaging, while larger or high-risk aneurysms may require surgical clipping or endovascular coiling. Lifestyle modifications—especially quitting smoking and controlling blood pressure—are crucial for all patients.