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Subarachnoid haemorrhage with negative early CT — SCE Acute Medicine MCQ

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HardAcute Neurological PresentationsSubarachnoid haemorrhage with negative early CTSCE Acute Medicine

A 45-year-old woman presents with sudden thunderclap headache during exercise. CT head performed eight hours after onset is reported normal. She remains photophobic and vomited twice. Neurological examination is normal and there is no fever. What is the most appropriate investigation?

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Correct answer: A — Lumbar puncture for xanthochromia at appropriate timing

A thunderclap headache with normal CT beyond the highly sensitive early window still requires further assessment for subarachnoid haemorrhage, traditionally LP for xanthochromia or specialist vascular imaging pathways. Discharge would miss sentinel SAH. Migraine is a diagnosis of exclusion in this context. The pearl is that timing of CT strongly affects its negative predictive value.

Reference: NICE NG228; UK neurovascular guidance