GPAtlas🧭 When to suspect
A subarachnoid haemorrhage (SAH) is bleeding into the subarachnoid space – most often from a ruptured berry (saccular) aneurysm of the Circle of Willis.
• It is a neurosurgical emergency: case fatality is high, and a substantial proportion of patients die before reaching hospital.
• Rebleeding in the first hours is the major preventable cause of early death.
• The only thing that matters in primary care is therefore rapid recognition and immediate transfer.
Suspect SAH in anyone presenting with a thunderclap headache – a sudden, severe (“worst headache of my life”) headache that reaches maximum intensity within 1 to 5 minutes.
• The speed of onset is the most important diagnostic feature – more so than the absolute severity of the pain.
• Most thunderclap headaches are not due to SAH, but that must never deter investigation.
• Act on the history alone and refer immediately, even when examination and observations are entirely normal.
Every thunderclap headache also has a short list of dangerous mimics – all of which need the same-day emergency pathway.
| Cause of thunderclap headache | Pointers and why it matters |
|---|---|
| Subarachnoid haemorrhage | The must-not-miss diagnosis – sudden agonising headache ± vomiting, neck stiffness, photophobia, altered consciousness or focal deficit. |
| Intracerebral haemorrhage | Headache with a focal neurological deficit and/or reduced consciousness. |
| Cervical artery dissection (carotid/vertebral) | • Younger patient • Neck or face pain, Horner’s syndrome, recent trauma or neck manipulation • High stroke risk |
| Cerebral venous sinus thrombosis | • Headache ± seizures or papilloedema • Prothrombotic states, pregnancy/puerperium, combined hormonal contraception |
| Reversible cerebral vasoconstriction syndrome (RCVS) | • Recurrent thunderclaps over days • Post-partum or after vasoactive drugs (including cocaine, decongestants) |
| Pituitary apoplexy | Sudden headache with visual field loss or ophthalmoplegia ± features of hypopituitarism. |
| Bacterial meningitis | Fever, meningism, photophobia ± non-blanching rash. |
| Spontaneous intracranial hypotension | Orthostatic headache (worse upright, relieved lying flat) from a cerebrospinal fluid (CSF) leak. |
Raise suspicion further with known risk factors:
• Smoking and hypertension (the strongest modifiable factors).
• Excess alcohol.
• A family history of SAH or aneurysm (especially two or more first-degree relatives).
• Autosomal dominant polycystic kidney disease, Ehlers-Danlos syndrome or coarctation of the aorta.
• Use of sympathomimetic drugs (e.g. cocaine).
• Increasing age and female sex.
|
🧠 Clinical pearl – the sentinel headache • In a minority of patients a small herald (“warning”) bleed produces a sudden, severe, self-limiting headache days to weeks before the major rupture. • A “worst-ever” headache that has since settled is therefore a red flag for an impending catastrophic bleed – not reassurance – and still warrants urgent investigation. |
Source: NICE NG228 · National Clinical Guideline for Stroke
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