A 65-year-old man presents with sudden onset severe headache ('thunderclap headache'), neck stiffness, and photophobia. CT head is normal. Lumbar puncture reveals xanthochromic CSF. This presentation is consistent with subarachnoid haemorrhage (SAH). The MOST common cause of non-traumatic SAH is:
- A Rupture of a saccular (berry) aneurysm at an arterial bifurcation in the circle of Willis ✓
- B Arteriovenous malformation (AVM) rupture
- C Hypertensive intracerebral haemorrhage extending into the subarachnoid space
- D Moyamoya disease in the elderly
Correct answer: A. Rupture of a saccular (berry) aneurysm at an arterial bifurcation in the circle of Willis
Explanation
Ruptured saccular (berry) aneurysms account for 80–85% of all non-traumatic subarachnoid haemorrhages. They arise at bifurcation points in the circle of Willis, most commonly at the anterior communicating artery (30%), posterior communicating artery (25%), and middle cerebral artery bifurcation (20%). Xanthochromia develops 2–4 hours after haemorrhage and persists for up to 2 weeks, distinguishing true SAH from traumatic lumbar puncture. AVMs account for ~5–10% and are more common in younger patients.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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