- Take the history carefully: this will identify all patients with true acute onset headache (maximal within seconds/minutes). All these patients require investigation.
- Provided the scan is done within 48 h of symptom onset, on a modern CT scanner, and interpreted by an experienced neuroradiologist, the sensitivity of CT imaging is very high, in excess of 95% (but crucially not 100%).
- All acute onset headache patients with a normal CT need a CSF examination, and you need to know how to interpret the results.
