Synopsis
Recognise suspected aneurysmal subarachnoid haemorrhage, use the time-dependent CT and lumbar-puncture diagnostic pathway correctly, identify the culprit aneurysm and apply clinical and radiological grades as descriptors rather than treatment gates.
- This pathway concerns spontaneous aneurysmal SAH, not traumatic subarachnoid blood. Suspect it after unexplained thunderclap headache or compatible collapse, seizure, reduced consciousness or focal signs.
- Urgent non-contrast CT is first line. If CT within 6 hours is negative and is reported and documented by a radiologist, NICE advises against routine LP; seek specialist advice and consider alternative diagnoses.
- If negative CT was done more than 6 hours after onset, consider LP; wait at least 12 hours from onset and diagnose SAH when CSF spectrophotometry shows elevated bilirubin. Do not use visual inspection alone.
Key red flags
Unexplained thunderclap headache requires urgent assessment even when neurological examination is normal or pain improves.
Collapse, seizure, reduced consciousness, focal deficit, cranial-nerve palsy, meningism or repeated vomiting strengthens suspicion and may indicate high-grade disease or a complication.
A negative CT more than 6 hours after symptom onset is less reliable; consider lumbar puncture, performed at least 12 hours after onset, for spectrophotometric bilirubin when it is safe.
Do not perform LP in cardiorespiratory instability, evolving focal signs, impaired consciousness suggesting mass effect, significant bleeding risk or an unsafe structural context.
Confirmed SAH with falling GCS, worsening focal signs, hydrocephalus or rebleeding requires immediate neurocritical and neurosurgical action, independent of the recorded grade.
A poor WFNS or Hunt-Hess grade must not be used alone to refuse transfer or aneurysm treatment; reversible hydrocephalus, seizure, sedation and physiology can alter the clinical grade.
Ask how quickly pain reached maximum intensity, the exact onset time and what the person was doing. Exertion, sexual activity or Valsalva may precede rupture, but spontaneous onset is also common. “Worst ever” wording is less useful than time to peak.
Assess consciousness, seizure, meningism, photophobia, vomiting, focal weakness, speech, eye movements and pupils. A third-nerve palsy with a dilated pupil raises concern for a posterior communicating artery aneurysm but does not replace vascular imaging.
Rebleeding, acute hydrocephalus, intraparenchymal extension, seizures and cardiopulmonary disturbance can worsen consciousness. Repeat examination and imaging are required when grade or physiology changes.
Reasoning priorities
Detect acute subarachnoid blood, intraventricular or parenchymal extension, hydrocephalus and mass effect.
Blood is often hyperdense in basal cisterns, fissures and sulci. A positive scan establishes SAH. For a negative scan, record onset-to-scan time and reporter: within 6 hours with radiologist reporting, NICE advises no routine LP; after 6 hours, consider LP.
Worked reasoning
An adult reports an unexplained headache reaching maximal intensity within one minute and has no persistent focal deficit.
- Arrange urgent senior assessment and non-contrast CT, recording exact onset-to-scan time; give effective analgesia and document opioid timing because sedation and pupil effects influence subsequent examination.
- If CT shows subarachnoid blood, urgently discuss transfer with a specialist neurosurgical centre and obtain CTA without delay. If CT is negative, choose the next step from the 6-hour timing and radiologist-reporting boundary.
- For a negative CT within 6 hours that is reported and documented by a radiologist, do not routinely offer LP; discuss with a senior decision-maker, seek specialist advice and evaluate alternative dangerous causes.
- For a negative CT after 6 hours with ongoing suspicion, consider LP when safe, timing it at least 12 hours after onset and sending spectrophotometry for bilirubin.
- If SAH is confirmed, assess clinical and CT severity, hydrocephalus and rebleeding while the specialist team plans early aneurysm securing.