1599-5453 Contact Us KO
Stroke

Cerebral Aneurysm

Cerebral Aneurysm · I67.1

A cerebral aneurysm is an abnormal outpouching of the brain's blood vessel wall caused by localized weakening, which balloons outward. When ruptured, it causes subarachnoid hemorrhage (SAH), a dangerous vascular malformation associated with high mortality and severe neurological sequelae.

2026-03-28

At a Glance

Cerebral aneurysms are found in approximately 2-5% of the adult population and are mostly asymptomatic. Rupture results in subarachnoid hemorrhage, presenting as the "worst headache of one's life," with a 30-day mortality rate of approximately 25-50%. They commonly occur around the Circle of Willis, particularly at the anterior communicating artery (ACoA) and posterior communicating artery (PCoA) junctions. Non-invasive diagnosis is possible with MRA or CTA, and endovascular coiling and surgical clipping are the primary treatments. Treatment decisions for unruptured aneurysms are based on comprehensive consideration of size, location, and patient factors.

Definition and Overview

A cerebral aneurysm (intracranial aneurysm) is an abnormal focal outpouching of the brain's blood vessel wall caused by structural weakening. It is a relatively common vascular malformation found in approximately 2-5% of the general population, but is a dangerous condition that can lead to subarachnoid hemorrhage (SAH) with high mortality when ruptured [1].

By sex, prevalence is approximately 1.5 times higher in women than men after age 40 [1]. Most cerebral aneurysms remain asymptomatic throughout life and are discovered incidentally, though some rupture. The annual rupture risk varies by size but is generally estimated at approximately 0.7-1.9% [4].

Location and Classification

Approximately 85% of cerebral aneurysms occur at vessel bifurcations around the Circle of Willis. The most common sites are the anterior communicating artery (ACoA, approximately 30%), the internal carotid artery-posterior communicating artery junction (ICA-PCoA junction, approximately 25%), and the middle cerebral artery bifurcation (MCA bifurcation, approximately 20%) [1].

Aneurysms are classified by morphology into saccular (approximately 90% of all cases), fusiform, and dissecting types. Saccular aneurysms are the most common and carry the highest rupture risk. By size, they are classified as small (<7 mm), medium (7-12 mm), large (13-24 mm), and giant (>=25 mm), with larger sizes associated with higher rupture risk [4].

Risk Factors

Among genetic factors, having two or more first-degree family members with cerebral aneurysms significantly increases the risk. Connective tissue disorders such as polycystic kidney disease, Ehlers-Danlos syndrome, and Marfan syndrome are associated risk factors.

Acquired risk factors include smoking (4-7 fold increased risk), hypertension, and excessive alcohol consumption as the major environmental factors [5]. In longitudinal studies of aneurysm growth, smoking was identified as the strongest predictor [5].

Rupture and Subarachnoid Hemorrhage

Ruptured cerebral aneurysm is the most common cause of subarachnoid hemorrhage (SAH), accounting for approximately 85% of cases. Upon rupture, blood rapidly enters the subarachnoid space, causing a sharp rise in intracranial pressure.

The 30-day mortality rate is approximately 25-50%, and approximately 50% of survivors are left with permanent neurological disability [2]. The risk of rebleeding within the first 24-48 hours after rupture is approximately 15-20%, necessitating prompt aneurysm obliteration [2].

Post-rupture complications include rebleeding, vasospasm (days 4-14, a cause of delayed cerebral ischemia), hydrocephalus (obstruction of cerebrospinal fluid circulation), hyponatremia, and cardiac abnormalities (neurogenic cardiac dysfunction).

Diagnosis

MRA (magnetic resonance angiography) and CTA (CT angiography) are used as non-invasive screening tests for unruptured aneurysms. Both methods have high sensitivity for detecting aneurysms 5 mm or larger. Digital subtraction angiography (DSA) is the standard examination for definitive diagnosis and treatment planning.

Non-contrast CT is the first-line choice for immediate diagnosis when subarachnoid hemorrhage is suspected. CT sensitivity within 6 hours of SAH onset is approximately 98%, but decreases over time. If CT is normal but SAH suspicion persists, lumbar puncture is performed to check for cerebrospinal fluid xanthochromia.

Treatment

Ruptured Aneurysm

Endovascular coiling and surgical clipping are the two primary treatments [3]. In the ISAT randomized controlled trial, coiling showed significantly higher 1-year independent survival compared to clipping (23.7% vs 30.6% mortality or dependent status, respectively) [3]. However, clipping may be more appropriate depending on the anatomical characteristics of the aneurysm.

Oral nimodipine is recommended for the prevention of vasospasm after rupture [2].

Unruptured Aneurysm

Treatment decisions are individualized by comparing rupture risk against treatment complication risk. In the ISUIA study, small aneurysms less than 7 mm in diameter (particularly in the anterior circulation) had a low annual rupture risk of less than 0.1%, suggesting that observation is a reasonable option [4].

Treatment is strongly considered for aneurysms 7 mm or larger, irregularly shaped aneurysms, those with daughter sacs, posterior circulation aneurysms, symptomatic aneurysms, and those demonstrating growth.

Frequently Asked Questions

A cerebral aneurysm is a condition where part of a brain blood vessel wall weakens and balloons outward. In most cases, it is discovered incidentally without symptoms. The concern is that if this bulging area ruptures, blood flows into the space surrounding the brain, creating a very dangerous situation. This is called subarachnoid hemorrhage. Since the aneurysm itself is a vascular malformation, it often causes no serious symptoms unless it ruptures.

Rupture causes a sudden "worst headache of one's life" (thunderclap headache). It is accompanied by nausea, vomiting, neck stiffness (nuchal rigidity), photophobia, and altered consciousness. Some patients may experience a "sentinel headache" days to weeks before rupture. If you experience these symptoms, visit the emergency room immediately. The longer the delay, the worse the prognosis.

Most are discovered incidentally when an MRI is performed for another reason. Screening is recommended if two or more family members have had cerebral aneurysms or subarachnoid hemorrhage. MRA (magnetic resonance angiography) and CTA (CT angiography) are used as non-invasive screening tests, and digital subtraction angiography (DSA) is performed for definitive diagnosis. If you have hypertension, a smoking history, or a strong family history, please discuss the need for screening with a specialist.

Both methods are safe and effective treatments for appropriate patients. Endovascular coiling involves inserting a catheter through the blood vessels and filling the aneurysm with coils, without open surgery. Surgical clipping involves opening the skull and placing a clip at the neck of the aneurysm. The ISAT study showed that coiling had higher 1-year independent survival rates than surgery for ruptured aneurysms. The decision is made in consultation with your physician, considering the aneurysm's location, size, shape, and the patient's age and overall condition.

Not all unruptured cerebral aneurysms require immediate treatment. If the size is less than 7 mm and the location is not high-risk, the rupture risk is low and observation is often chosen. The decision is based on comparing rupture risk against treatment complication risk. A comprehensive evaluation includes size, shape (irregular morphology, daughter sac), location, growth status, patient age and overall condition, and risk factors such as hypertension and smoking. Imaging follow-up at 1-2 year intervals monitors for size changes.

When an unruptured cerebral aneurysm is discovered, caution with certain activities may be necessary. Recommendations may include avoiding actions that cause sudden blood pressure spikes (heavy lifting, forceful coughing, intense exercise). Smoking cessation, blood pressure management, and moderate alcohol consumption are important. However, most daily activities remain possible. Please discuss specifically with your physician what is permitted and what should be avoided.

References

  1. [1] Vlak MH, Algra A, Brandenburg R, Rinkel GJ (2011). "Prevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis." The Lancet Neurology, 10: 626-636. DOI PubMed
  2. [2] Nieuwkamp DJ, Setz LE, Algra A, Linn FH, de Rooij NK, Rinkel GJ (2009). "Changes in case fatality of aneurysmal subarachnoid haemorrhage over time, according to age, sex, and region: a meta-analysis." The Lancet Neurology, 8: 635-642. DOI PubMed
  3. [3] Molyneux AJ, Kerr RS, Yu LM, Clarke M, Sneade M, Yarnold JA, et al. (2005). "International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion." The Lancet, 366: 809-817. DOI PubMed
  4. [4] Wiebers DO, Whisnant JP, Huston J, Meissner I, Brown RD, Piepgras DG, et al. (2003). "Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment." The Lancet, 362: 103-110. DOI PubMed
  5. [5] Juvela S, Poussa K, Porras M (2001). "Factors affecting formation and growth of intracranial aneurysms: a long-term follow-up study." Stroke, 32: 485-491. DOI PubMed

Related Articles

Stroke Rehabilitation
Cerebral AneurysmIntracranial AneurysmSubarachnoid HemorrhageRuptured AneurysmAneurysm CoilingClipping

This content is provided for medical information purposes only and cannot replace professional medical advice. If you have symptoms, please consult a specialist.

Are you concerned about related symptoms?

Get an accurate diagnosis at OSANG Neurosurgery.

02-514-8887 Contact Us