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Thunderclap headache with negative early CT — RCPSC EM MCQ

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HardNeurological emergenciesThunderclap headache with negative early CTRCPSC EM

CTAS 2: A 45-year-old has sudden worst headache reaching maximal intensity within seconds during exertion. Vitals are BP 154/88, HR 92, and neurologic exam is normal. Non-contrast CT head at 10 hours from onset is read as normal. No anticoagulant use is reported. What is the most appropriate investigation?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — Lumbar puncture for xanthochromia and opening pressure

A normal CT performed beyond the early high-sensitivity window does not safely exclude subarachnoid haemorrhage in a high-risk thunderclap headache. LP or CTA pathway is needed depending on local policy.

Reference: Ottawa SAH Rule literature; Canadian EM headache practice