Subarachnoid hemorrhage (SAH) refers to bleeding into the subarachnoid space, the area between the arachnoid membrane and pia mater surrounding the brain. This space normally contains cerebrospinal fluid (CSF), and bleeding here increases intracranial pressure and irritates the meninges.
SAH is a neurological emergency with high morbidity and mortality. It accounts for around 5–10% of all strokes, but carries a much higher risk of death or long-term disability compared to ischemic stroke.
The causes of SAH can be remembered using the mnemonic BATS.
Mnemonic: BATS (Causes of SAH)
| Letter | Cause | Explanation |
|---|---|---|
| B | Berry aneurysm | Rupture of congenital saccular aneurysms at circle of Willis bifurcations |
| A | Arteriovenous malformation (AVM) / Adult polycystic kidney disease | Vascular malformations or genetic conditions linked to aneurysms |
| T | Trauma | Head injury is the most common overall cause of SAH |
| S | Stroke | Hemorrhagic stroke causing vessel rupture |
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Detailed Causes
1. Berry Aneurysm
Most common non-traumatic cause of SAH.
Congenital saccular aneurysms, often located at arterial bifurcations of the Circle of Willis.
Risk factors:
- Hypertension
- Smoking
- Polycystic kidney disease
- Ehlers-Danlos syndrome
Clinical Note: Ruptured berry aneurysms cause sudden severe headache (“thunderclap headache”).
2. Arteriovenous Malformations (AVM) / Adult Polycystic Kidney Disease
- AVMs are abnormal tangles of arteries and veins without intervening capillaries → fragile and prone to rupture.
- Adult polycystic kidney disease is strongly associated with berry aneurysms → raises SAH risk.
- Often present in younger patients with recurrent headaches or seizures before rupture.
3. Trauma
- Most common overall cause of SAH.
- Seen in falls, road traffic accidents, assaults (e.g., baseball bat injury as noted in your mnemonic card).
- Bleeding typically occurs over cerebral convexities.
- May coexist with subdural or epidural hemorrhage.
4. Stroke
- Hemorrhagic stroke due to uncontrolled hypertension or anticoagulant therapy can lead to SAH.
- Less common than aneurysmal or traumatic causes.
Risk Factors for SAH
- Hypertension
- Smoking
- Family history of aneurysms or SAH
- Connective tissue disorders (Marfan syndrome, Ehlers-Danlos)
- Polycystic kidney disease
- Excessive alcohol use
Clinical Features
- Sudden severe headache (“worst headache of my life” / thunderclap headache)
- Nausea, vomiting
- Photophobia, neck stiffness (meningeal irritation)
- Loss of consciousness
- Seizures
- Focal neurological deficits (if aneurysm compresses brain tissue or causes vasospasm)
Diagnosis
1. Neuroimaging
- CT scan (non-contrast): First-line, detects acute SAH with >90% sensitivity within 24 hrs.
- MRI: More sensitive in delayed presentations.
2. Lumbar Puncture
- Performed if CT is negative but suspicion remains high.
- Xanthochromia (yellow CSF due to hemoglobin breakdown) confirms SAH.
- CT angiography or cerebral angiography identifies aneurysms or AVMs.
Management
Initial Stabilization
- Secure airway, breathing, circulation.
- Control blood pressure (avoid extremes).
- Pain management and prevention of rebleeding.
Specific Treatment
- Aneurysmal SAH: Endovascular coiling or surgical clipping.
- AVM: Resection, embolization, or radiosurgery.
- Traumatic SAH: Supportive management, control of intracranial pressure.
Complications to Monitor
- Rebleeding (highest risk in first 24 hrs).
- Cerebral vasospasm → delayed ischemia.
- Hydrocephalus (due to blocked CSF reabsorption).
- Hyponatremia (SIADH).
Prognosis
- Mortality: 25–50% even with treatment.
- Many survivors have neurological deficits.
- Early intervention and neurocritical care improve outcomes.
Quick Reference – BATS Mnemonic
| Mnemonic | Cause |
|---|---|
| B | Berry aneurysm |
| A | AVM / Adult polycystic kidney disease |
| T | Trauma |
| S | Stroke |
FAQs
1. What is the most common cause of non-traumatic SAH?
Berry aneurysm rupture.
2. Can SAH happen in young people?
Yes, especially with AVMs or genetic conditions like polycystic kidney disease.
3. Why is SAH so dangerous?
Because of risks of rebleeding, vasospasm, and sudden death from increased intracranial pressure.
4. How can berry aneurysm be prevented?
Managing hypertension, quitting smoking, and screening high-risk patients with family history.
5. What is the gold standard for aneurysm treatment?
Endovascular coiling or surgical clipping, depending on aneurysm location and patient condition.
