A 65-year-old man presents with sudden-onset severe headache ('thunderclap headache'), neck stiffness, and photophobia. CT brain is normal. Lumbar puncture shows xanthochromia and elevated red cell count that does not decrease in successive tubes. The most common cause of spontaneous subarachnoid haemorrhage is:

• A Saccular (berry) aneurysm rupture ✓
• B Arteriovenous malformation (AVM)
• C Hypertensive intracerebral haemorrhage
• D Coagulopathy-related bleeding

Explanation

Spontaneous subarachnoid haemorrhage (SAH) is caused by rupture of a saccular (berry) aneurysm in approximately 80% of cases. Berry aneurysms develop at vessel bifurcations (most commonly at the anterior communicating artery junction). The classic presentation is 'worst headache of life', meningism, and xanthochromia on LP (if CT is negative, LP is diagnostic). AVM accounts for approximately 10% of non-traumatic SAH. CT sensitivity falls to < 90% beyond 12 hours from ictus, making LP essential.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.