Subarachnoid Hemorrhage
Neurology
Illness script · Neurology
Subarachnoid Hemorrhage
Bleeding into the subarachnoid space, most often from a ruptured intracranial aneurysm, causing sudden severe headache.
This illness script for Subarachnoid Hemorrhage covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Peak incidence 40–60 years; women slightly > men
- Saccular (berry) aneurysms at Circle of Willis bifurcations (~85% of cases)
- Risk factors: hypertension, smoking, heavy alcohol use
- Associated with ADPKD, Ehlers-Danlos, Marfan syndrome
- Family history of aneurysm or prior SAH increases risk
- Cocaine use → acute BP surge → rupture
02
Presentation
- 'Thunderclap' headache — worst headache of life, maximal at onset
- Sentinel headache (warning leak) days–weeks prior in ~20%
- Meningismus: nuchal rigidity, Kernig's & Brudzinski's signs
- Photophobia, nausea/vomiting, brief LOC at ictus
- Focal deficits uncommon unless CN III palsy (posterior communicating artery aneurysm)
- Fundoscopy: subhyaloid (preretinal) hemorrhage — pathognomonic
03
Pathophysiology
- Aneurysm rupture → arterial blood floods subarachnoid space under high pressure
- Sudden ICP spike → transient global ischemia → thunderclap onset
- Blood breakdown products → vasospasm (peaks days 4–14) → delayed cerebral ischemia
- Hydrocephalus from CSF outflow obstruction by blood clot
04
Diagnostics
- Non-contrast head CT first-line: hyperdense blood in basal cisterns (sensitive >98% within 6h)
- Lumbar puncture if CT negative but clinical suspicion high: xanthochromia (yellow CSF) after 2–4h
- CT angiography to identify aneurysm; DSA (digital subtraction angiography) is gold standard
- ECG changes (diffuse T-wave inversions, QT prolongation) common — do not misdiagnose as MI
- Hunt-Hess grade (clinical) and Fisher grade (CT blood) guide prognosis
05
Management
- Secure airway; strict BP control (target SBP <160 mmHg) until aneurysm secured
- Neurosurgical clipping OR endovascular coiling to secure aneurysm (coiling preferred if anatomy allows)
- Nimodipine (oral) 60 mg q4h × 21 days — reduces vasospasm-related ischemia
- Avoid anticoagulants and antiplatelet agents until aneurysm secured
- Monitor for re-bleeding (highest risk first 24h), vasospasm (days 4–14), hydrocephalus, hyponatremia (SIADH/cerebral salt wasting)
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Migraine
Migraine builds over minutes–hours; SAH is maximal at onset (thunderclap) — never assume migraine without ruling out SAH
Meningitis
Meningitis fever and gradual headache onset; SAH headache is instantaneous and CSF shows xanthochromia not just pleocytosis
Hypertensive Emergency (Hypertensive Encephalopathy)
Hypertensive encephalopathy has gradual onset with papilledema; SAH has sudden-onset headache with blood on CT/LP
Cervical Artery Dissection
Dissection causes neck pain + focal neuro deficits; SAH has meningismus and basal cistern blood on CT
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.