A 55-year-old man presents with sudden severe headache ('worst headache of his life'), neck stiffness, and photophobia. CT brain is negative. What is the NEXT diagnostic step and the MOST common cause of this presentation?
- A Lumbar puncture for CSF xanthochromia; most common cause is ruptured berry aneurysm (subarachnoid haemorrhage) ✓
- B MRI brain immediately; most common cause is migraine
- C EEG; most common cause is partial seizure with postictal headache
- D Cerebral angiography immediately without lumbar puncture
Correct answer: A. Lumbar puncture for CSF xanthochromia; most common cause is ruptured berry aneurysm (subarachnoid haemorrhage)
Explanation
A thunderclap headache with meningism in a normal-CT patient requires lumbar puncture to look for xanthochromia (yellow CSF discoloration from haemoglobin breakdown products) — seen 2-4 hours after bleed and persists for up to 2 weeks. CT has 98% sensitivity within 12 hours but sensitivity drops thereafter. The most common cause of spontaneous subarachnoid haemorrhage is a ruptured saccular (berry) aneurysm (~85% of cases), typically at the circle of Willis bifurcations.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.