Synopsis
Recognise aneurysmal subarachnoid haemorrhage, apply the time-dependent CT and lumbar-puncture diagnostic pathway, and coordinate aneurysm securing and prevention of rebleeding, hydrocephalus and delayed cerebral ischaemia.
- Suspect subarachnoid haemorrhage when a new severe headache reaches peak intensity within minutes, especially with neck stiffness, vomiting, photophobia, collapse, seizure or focal deficit.
- A normal neurological examination does not exclude SAH; many alert patients have only headache at presentation, and a sentinel headache may precede a larger aneurysmal bleed.
- Obtain urgent non-contrast CT brain, document the interval from onset and ensure expert interpretation because sensitivity is highest in the first 6 hours and decreases thereafter.
- If a high-quality CT performed within 6 hours is reported negative by an appropriate radiologist, NICE advises not routinely performing lumbar puncture; if CT occurs after 6 hours and is negative, consider LP after at least 12 hours from onset.
- When CT confirms SAH, perform CTA without delay to identify an aneurysm and involve a specialist neurosurgical or neurointerventional centre immediately; catheter angiography may be required when CTA is negative or treatment planning needs it.
- Secure a ruptured aneurysm as early as feasible by endovascular coiling or neurosurgical clipping through multidisciplinary assessment; rebleeding risk is greatest before definitive treatment.
- Offer enteral nimodipine unless contraindicated to reduce poor outcome from delayed cerebral ischaemia, and monitor pressure because hypotension can compromise cerebral perfusion.
- Watch for hydrocephalus, delayed cerebral ischaemia, seizures, hyponatraemia, fever, cardiac injury, pulmonary oedema and venous thrombosis throughout neurocritical care.
Key red flags
Reduced consciousness, airway compromise, recurrent seizure or cardiorespiratory instability requires immediate resuscitation and neurocritical-care involvement.
A new painful oculomotor palsy with pupillary dilation may signal an enlarging or recently ruptured posterior communicating aneurysm and warrants emergency vascular imaging.
Sudden recurrent headache or decline before aneurysm treatment suggests rebleeding and needs immediate CT and neurovascular escalation.
Progressive drowsiness, downward gaze or worsening headache with ventricular enlargement indicates acute hydrocephalus and a possible urgent CSF-diversion requirement.
New neurological deficit days after securing the aneurysm may be delayed cerebral ischaemia and must not be attributed automatically to fatigue or sedating medicines.
Investigation priorities
Detect subarachnoid blood, hydrocephalus, intraventricular or intracerebral extension and early mass effect.
Management branches
A patient has a new severe headache reaching maximum intensity within minutes.
- Assess airway, consciousness, focal neurology, pupils, meningism, seizure, pressure and antithrombotic exposure and treat immediate instability.
- Arrange urgent non-contrast CT and record exact onset and scan times, providing the radiologist with the suspected SAH diagnosis.
- If CT is positive, contact the neurovascular centre and obtain CTA; if negative, apply the 6-hour NICE pathway and the continuing clinical level of suspicion.
- Keep safety advice and alternative thunderclap diagnoses active even if SAH is excluded, including dissection, venous thrombosis, RCVS and pituitary apoplexy.