Berry aneurysm and subarachnoid hemorrhage
- Lesion
A berry aneurysm is a thin pouch at a fork of the brain's arteries; when it bursts, blood fills the space around the brain.
What it is
Saccular aneurysms are the commonest cause of nontraumatic subarachnoid hemorrhage. They form at branch points of the circle of Willis, where the muscular media is naturally deficient, and grow over years. Rupture floods the subarachnoid space with blood under arterial pressure, causing the ‘worst headache of life’, and is followed by dangerous vasospasm and hydrocephalus. Other aneurysm types (mycotic, fusiform, traumatic) are less common.
Step by step
- Hemodynamic stress acts on a branch point where the media is thin.
- The wall degenerates, the elastic lamina fragments and a pouch bulges out.
- Smoking and hypertension speed growth; a larger sac is more likely to rupture.
- Rupture, often with straining, pours blood into the subarachnoid space.
- Blood breakdown products trigger arterial spasm and delayed infarction.
- Organising blood in the meninges blocks CSF absorption and causes hydrocephalus.
Intracranial aneurysm types
| Type | Shape and site | Cause |
|---|---|---|
| Saccular (berry) | Round pouch at branch points of the circle of Willis | Acquired degeneration at a site with thin media |
| Fusiform | Spindle-shaped dilatation, often basilar | Atherosclerosis |
| Mycotic (infectious) | Distal branches | Septic emboli, usually from infective endocarditis |
| Traumatic or dissecting | Any artery | Trauma, arterial dissection |
Clinical notes
- Sudden severe headache with neck stiffness and vomiting; CT shows blood in the basal cisterns, and lumbar puncture shows xanthochromia if CT is negative.
- Screening relatives and patients with polycystic kidney disease is considered when there is a family history.
Test yourself
Think of the answer, then tap the question to see it.
What is missing from the wall of a saccular aneurysm?
The muscular media; the internal elastic lamina is fragmented and the sac is made of intima and adventitia.
Which kidney disease is associated with berry aneurysms?
Autosomal dominant polycystic kidney disease.
When is vasospasm most likely after aneurysmal subarachnoid hemorrhage?
Roughly from day three to day fourteen, causing delayed ischemic deficits.
Elsewhere in DurgiPedia
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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Subarachnoid Hemorrhage (StatPearls (NCBI Bookshelf), 2026); Autosomal Dominant Polycystic Kidney Disease (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.