Cerebral aneurysm (intracranial / brain aneurysm)

A cerebral aneurysm is a focal outpouching of a brain artery wall. Many are never detected; a minority rupture and cause aneurysmal subarachnoid hemorrhage (aSAH), a medical emergency.

Aneurysms usually occur at branch points

The majority of saccular (“berry”) aneurysms arise on the circle of Willis and its major branches. The diagram is provided to help you orient common locations discussed throughout this site.

Image: public domain (Wikimedia Commons).

Circle of Willis diagram
Most are unruptured and found incidentally
Rupture can be catastrophic (aSAH)
Risk can be stratified by size, location, history, blood pressure, smoking, etc.
~3% of adults
Estimated prevalence of unruptured intracranial aneurysm in population studies
~8 / 100,000 / year
Approx. global incidence of aneurysmal SAH (varies by region)
Rupture risk varies
Often low for small anterior‑circulation aneurysms, higher for larger/posterior aneurysms
Treat vs observe
Decision balances natural rupture risk vs procedural risk and patient factors
Urgent symptoms: sudden “thunderclap” headache, collapse, seizure, stiff neck, new weakness, speech or vision changes — call emergency services immediately.

What is it, structurally?

Most cerebral aneurysms are saccular (“berry”) aneurysms at branching points of the Circle of Willis. The arterial wall is weakened and bulges outward.

Aneurysms may be:

  • Small (often <7 mm) and incidental
  • Large / giant (higher rupture and mass‑effect risk)
  • Fusiform / dissecting (different biology and treatment approach)

Symptoms when unruptured are uncommon, but can occur from mass effect (e.g., cranial nerve palsy causing double vision).

Short explainer video (general aneurysm basics)

A 10‑minute CC‑licensed educational video explaining what an aneurysm is and why aneurysm walls can weaken. (It is not specific to the brain, but the principles apply.)

Video: Osmosis, CC BY‑SA 4.0 (Wikimedia Commons).

Key decisions after discovery

Most management discussions center on three questions:

  1. What is the short‑ and long‑term rupture risk?
  2. What is the risk of treatment (open surgery vs endovascular) in this patient and aneurysm anatomy?
  3. What matters to the patient? (age, comorbidity, anxiety, occupation, pregnancy plans, access to follow‑up)
Aneurysm care is best handled in a center that offers both microsurgical and endovascular options, enabling a tailored recommendation.
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