Thunderclap headache and SAH exclusion pathway

Recognition. This is a thunderclap headache (maximal intensity within seconds) triggered by Valsalva — treat as subarachnoid haemorrhage until proven otherwise. Positive SNNOOP items include Onset sudden and Precipitated by Valsalva; age near the classic SAH demographic. Primary migraine is a diagnosis of exclusion after the dangerous pathway is cleared.^[3]

Immediate assessment. ABCDE; two IV cannulae; ECG; bloods (FBC, U&E, coags, group-and-save); document full neurological examination including fundoscopy (papilloedema would open mass/CVST/IIH pathways), neck stiffness, and absence of fever (still does not exclude SAH). Control severe pain (e.g. opioids titrated); avoid hypoxia/hypotension.^[3]

CT pathway. Urgent non-contrast CT head now (onset-to-scan well under 6 hours). If performed within 6 hours of onset on a modern scanner and reported by a qualified radiologist as no SAH, sensitivity is 100% (95% CI 97.0–100) and many contemporary pathways allow omission of LP when these criteria are strictly met.^[1][3] If CT is delayed beyond 6 hours, non-expert read, or residual high suspicion, proceed to LP (ideally ≥12 hours from onset for xanthochromia spectrophotometry), looking for red cells that do not clear and xanthochromia.

If SAH confirmed. Urgent neurosurgical referral; CTA for aneurysm; admit ICU/HDU; nimodipine 60 mg orally every 4 hours for 21 days (if able to swallow/NG), which cut cerebral infarction (22% vs 33%) and poor outcome (20% vs 33%) in the 554-patient trial, per local protocol; BP management per neurosurgical guidance; reverse anticoagulation if present; watch for rebleeding and hydrocephalus (dropping GCS → repeat CT).^[4]

Safety. Never label first thunderclap as migraine in ED without imaging pathway completion. Document clock times of onset and CT.^[3]