Sudden Worst Headache with a Normal Initial CT
A 48-year-old smoker presents 18 hours after a sudden-onset "worst headache of my life" that peaked within seconds while lifting a box. He has neck stiffness and photophobia but no focal deficit and a GCS of 15. Non-contrast CT performed 12 hours after onset is reported as normal by a radiology trainee. Blood pressure is 150/90 mmHg. There is no family history of aneurysms. The emergency department asks whether he can be discharged with analgesia.
1. How do you interpret the CT result, and what is the next diagnostic step? Justify the timing and the choice of test.
Read the worked answer
A normal non-contrast CT does not exclude subarachnoid haemorrhage, particularly beyond 6 hours and when read by a less experienced reporter. Sensitivity of CT for subarachnoid blood is highest within 6 hours (near 100% with modern scanners and expert review) and falls thereafter; at 12–18 hours a normal scan is reassuring but not definitive in a patient with a classic thunderclap history.
The next step is lumbar puncture for xanthochromia, ideally at least 12 hours after onset so that bilirubin has formed; spectrophotometry is preferred over visual inspection. Alternatively, CT angiography can be performed to look for an aneurysm, but a negative CTA does not exclude a small haemorrhage and does not replace CSF analysis in this scenario. Do not discharge.
The history - abrupt maximal onset, neck stiffness, photophobia, smoking - is high risk and warrants admission and investigation regardless of the initial report. Request re-review of the CT by a neuroradiologist as well.
2. The lumbar puncture shows uniformly blood-stained CSF that does not clear between tubes. How do you interpret this, and what are the risks and subsequent steps?
Read the worked answer
Uniform blood staining that does not clear is concerning for subarachnoid haemorrhage, but a traumatic tap can also produce blood throughout. The discriminating test is spectrophotometry for xanthochromia (bilirubin), which is specific for true haemorrhage; visual inspection is unreliable. If xanthochromia is present, the diagnosis is confirmed.
Risks of lumbar puncture in this setting include herniation if there is raised ICP (unlikely with GCS 15 and no focal deficit) and rebleeding, which is the main concern - the highest risk period is the first 24–48 hours. Therefore, once subarachnoid haemorrhage is suspected, the patient should be admitted, kept in a quiet environment, given analgesia, and have blood pressure controlled, with definitive vascular imaging (CT angiography, or catheter angiography if CTA is negative but suspicion remains) arranged urgently.
Subsequent steps: confirm the diagnosis, identify the aneurysm, discuss clipping versus coiling with the neurovascular team, start nimodipine, and monitor for hydrocephalus and vasospasm. If xanthochromia is negative and CTA is negative, the diagnosis becomes much less likely, but the patient still needs review.