A 60-year-old hypertensive man presents with sudden-onset thunderclap headache ('worst headache of my life'). CT head (plain) is performed within 6 hours of onset and is normal. The next diagnostic step is:

• A MRI brain with gadolinium
• B Lumbar puncture for xanthochromia — analyse CSF at least 12 hours after headache onset ✓
• C CT angiography of cerebral vessels
• D Repeat CT head at 24 hours

Explanation

Thunderclap headache with a normal CT head within 6 hours requires a lumbar puncture to exclude subarachnoid haemorrhage (SAH); the LP should be performed at least 12 hours after headache onset to allow xanthochromia (spectrophotometric detection of oxyhaemoglobin/bilirubin) to develop, as red cells may be present only transiently. CT angiography is performed after SAH is confirmed to identify the source aneurysm.

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

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Written and medically reviewed by the StethoPrep medical team.