A 45-year-old man presents with a sudden severe 'thunderclap' headache reaching maximum intensity within 60 seconds. CT head is performed within 6 hours and is negative for subarachnoid haemorrhage. What is the most appropriate immediate next investigation?
- A MRI brain with FLAIR sequence
- B CT angiography (CTA) of the circle of Willis
- C Repeat CT head after 24 hours
- D Lumbar puncture for xanthochromia ✓
Explanation
A negative CT head within 6 hours of symptom onset does not definitively exclude subarachnoid haemorrhage (SAH) — CT sensitivity drops from ~98% within 6 hours to ~85–90% at 12–24 hours. Lumbar puncture examining for xanthochromia (yellow discolouration of CSF from haemoglobin breakdown to bilirubin/oxyhaemoglobin, detectable 2 hours to 2 weeks after haemorrhage) is mandatory after a negative CT. CTA is performed after SAH is confirmed to identify the aneurysm source. The Ottawa SAH Rule and Perry et al. validated criteria support CT ± LP for thunderclap headache investigation.
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.