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Subarachnoid hemorrhage (SAH)
A sudden headache that peaks within a minute ("thunderclap headache") is subarachnoid haemorrhage until proven otherwise; most cases come from a ruptured aneurysm, and all care is built around preventing rebleeding and delayed ischaemia.
Why it matters in the exam
Questions describe the "worst headache of my life", sometimes with collapse, vomiting and neck stiffness. They ask when CT is enough and when a lumbar puncture is needed, which drug improves outcome (nimodipine), when vasospasm appears, and what causes hyponatraemia. A classic associated sign is a 3rd nerve palsy with a dilated pupil, which points to a posterior communicating artery aneurysm. Remember that some patients report a milder warning headache in the days before rupture and that the neurological exam can be entirely normal; the decision to image rests on how the pain began, not on its severity or the exam.
Key points
- A thunderclap headache is SAH until proven otherwise, even with a normal exam.
- CT within 6 hours almost excludes it; after 6 hours a normal CT requires a lumbar puncture.
- Find the aneurysm with CTA or DSA and secure it early, preferably within 24 hours.
- Oral nimodipine, 60 mg 4-hourly for 21 days, improves outcome.
- Vasospasm and delayed ischaemia on days 3 to 14; never fluid-restrict hyponatraemia.
Summary table
| Stage | What to do | Key detail |
|---|---|---|
| Diagnosis | Non-contrast CT; within 6 hours of headache onset its sensitivity is close to complete | After 6 hours, if CT is normal — lumbar puncture for xanthochromia (ideally 12 hours or more after onset) |
| Ottawa rule | Age 40 or more, neck pain or stiffness, witnessed loss of consciousness, onset with exertion, instant peak, limited neck flexion | If none is present the risk is very low |
| Finding the aneurysm | CTA, and angiography (DSA) as the gold standard | Secure the aneurysm (coil or clip) as early as possible, preferably within 24 hours |
| Preventing late damage | Nimodipine 60 mg orally every 4 hours for 21 days; keep normal volume (euvolemia) | Vasospasm and delayed ischaemia occur mainly on days 3 to 14 |
| Other complications | Rebleeding (mainly on the first day), hydrocephalus, hyponatraemia, seizures | Do not fluid-restrict in hyponatraemia, because cerebral salt wasting is possible |
A free exam question
בת 41 , מאושפזת בנוירוכירורגיה אחרי דימום תת עכבישי. ביום החמישי של האשפוז מפתחת סימנים חדשים של חולשה בגפיים ימניות ודיספזיה CT מוח חוזר ללא חומר ניגוד שלל דימום. חוזר. איזה טיפול היה יכול להפחית את הסיכוי לתופעות נוירולוגיות אלה? (the question as examined, in Hebrew)
- א. aspirin
- ב. factor VII
- ג. nimodipine
- ד. mannitol
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Sources
- AHA/ASA Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage, 2023 — Diagnosis, aneurysm repair and delayed cerebral ischemia
- Ottawa Subarachnoid Hemorrhage Rule (Perry et al., JAMA), 2013 — Clinical decision rule for acute headache
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.