A 60-year-old woman presents with sudden-onset severe headache described as 'thunderclap' — the worst headache of her life — with meningism. CT brain is performed within 6 hours and appears normal. What is the immediate next investigation?
- A MRI brain with gadolinium
- B CT angiography of cerebral vessels
- C Lumbar puncture for CSF examination (xanthochromia) ✓
- D EEG
Explanation
The clinical presentation of sudden-onset thunderclap headache is subarachnoid haemorrhage (SAH) until proven otherwise. CT brain detects SAH in 98% of cases within 6 hours, but when CT is normal and SAH is strongly suspected, lumbar puncture must be performed to look for xanthochromia (yellowish discoloration of CSF from breakdown of RBCs into bilirubin) and elevated red blood cells that fail to diminish between tube 1 and tube 4 (distinguishing SAH from a traumatic tap). Xanthochromia on spectrophotometry is detectable 2-4 hours after onset and persists for up to 2 weeks. A normal CT plus normal LP essentially excludes SAH.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.