Subarachnoid Hemorrhage (SAH)

A 46-year-old female presents to the emergency department with sudden onset of the worst headache of her life that reached maximal intensity within seconds while exercising. She reports nausea, vomiting, photophobia, and neck stiffness. She denies previous similar headaches. Blood pressure is 165/95 mm Hg, heart rate is 96 beats per minute, and she is alert and oriented. Neurologic examination shows no focal deficit. Noncontrast head CT demonstrates acute subarachnoid blood within the basal cisterns and sylvian fissures. Diagnosis?

Diagnosis is Acute Subarachnoid Hemorrhage (SAH).

1. Initial Approach to Acute Headache

The priority in a patient with acute headache is to identify dangerous secondary causes before diagnosing a primary headache disorder.

A practical approach is:

STABILIZE → IDENTIFY RED FLAGS → PRIMARY vs SECONDARY → DEFINE PHENOTYPE → TARGETED TESTING → TREAT THE CAUSE

A normal neurologic examination does not exclude serious secondary headache, including SAH.

2. Headache Red Flags: SNOOP+

2.1 Systemic Features

1.      Fever

2.      Unintentional weight loss

3.      Known malignancy

4.      Immunosuppression

5.      Pregnancy or postpartum state

6.      Systemic inflammatory or infectious disease

2.2 Neurologic Features

1.      Focal neurologic deficit

2.      Altered mental status

3.      Seizure

4.      Papilledema

5.      Persistent visual loss

2.3 Sudden Onset

1.      Thunderclap headache reaches maximal intensity within approximately 1 minute

2.      A new thunderclap headache requires urgent evaluation for a secondary vascular cause

2.4 Older Age

New headache beginning after approximately 50 years of age should raise concern for causes such as:

1.      Giant cell arteritis

2.      Malignancy

3.      Structural intracranial disease

2.5 Pattern Change

Important features include:

1.      First or worst headache

2.      Progressively worsening headache

3.      New headache phenotype

4.      Increasing frequency or severity

2.6 Additional Red Flags

1.      Positional headache

2.      Triggered by cough, Valsalva, exertion, or sexual activity

3.      Recent trauma

4.      Anticoagulant use

5.      Painful red eye

6.      New headache during pregnancy or postpartum

3. Thunderclap Headache

A thunderclap headache should prompt urgent evaluation for subarachnoid hemorrhage until adequately excluded.

Important differential diagnoses include:

1.      Subarachnoid hemorrhage

2.      Reversible cerebral vasoconstriction syndrome (RCVS)

3.      Cerebral venous sinus thrombosis (CVST)

4.      Cervical artery dissection

5.      Pituitary apoplexy

6.      Intracerebral hemorrhage

A normal neurologic examination does not exclude SAH.

4. Subarachnoid Hemorrhage

4.1 Clinical Features

Typical features include:

1.      Sudden severe thunderclap headache

2.      Headache reaching maximal intensity rapidly

3.      Nausea and vomiting

4.      Neck stiffness or meningismus

5.      Photophobia

6.      Transient or persistent loss of consciousness

7.      Seizure

8.      Focal neurologic deficits may occur but can be absent

A patient may therefore have SAH despite being awake, neurologically intact, and hemodynamically stable.

4.2 Initial Diagnostic Test

The initial investigation for suspected SAH is:

Noncontrast head CT

Presentation within 6 hours

In an appropriately selected neurologically intact patient with nontraumatic headache, a normal high-quality noncontrast head CT performed within 6 hours of symptom onset can rule out SAH when imaging quality and interpretation are adequate.

If clinical suspicion remains high despite a negative CT, additional evaluation remains appropriate.

Presentation ≥6 hours or new neurologic deficit

1.      Obtain noncontrast head CT

2.      If CT is negative but suspicion for SAH remains, lumbar puncture is recommended in the AHA/ASA diagnostic pathway

3.      ACEP guidance allows LP or CTA in selected patients who remain at risk after a negative CT

4.      The choice between LP and CTA should consider the clinical context, test limitations, and shared decision-making

4.3 Lumbar Puncture

When indicated after a negative CT, CSF evaluation may demonstrate:

1.      Elevated red blood cells

2.      Xanthochromia

Findings must be interpreted in the context of a possible traumatic lumbar puncture.

LP is particularly important when presentation is delayed and clinical suspicion remains high despite negative CT imaging.

4.4 Vascular Imaging

Once SAH is identified, vascular imaging is required to determine the bleeding source.

1.      CTA is commonly obtained first to identify an intracranial aneurysm

2.      If CTA is negative or inconclusive and aneurysmal SAH remains suspected, digital subtraction angiography (DSA) is indicated

3.      In diffuse basal cistern or sylvian fissure SAH, DSA should be strongly pursued because small aneurysms or other vascular lesions may not be adequately identified on CTA

A diagnosis of aneurysmal SAH requires identification of an aneurysmal source, rather than CT evidence of subarachnoid blood alone.

5. Ottawa SAH Rule

In an appropriate alert patient with a new severe nontraumatic headache reaching maximal intensity within 1 hour, further investigation for SAH is indicated if any of the following are present:

1.      Age ≥40 years

2.      Neck pain or stiffness

3.      Witnessed loss of consciousness

4.      Onset during exertion

5.      Thunderclap headache

6.      Limited neck flexion on examination

The Ottawa SAH Rule is a screening rule, not a diagnostic test, and applies only to the population in which it was validated.

6. Other High-Yield Secondary Headaches

6.1 Meningitis

Fever + headache + meningismus ± altered mental status

Consider meningitis or encephalitis.

Evaluation may require:

1.      Blood cultures

2.      Neuroimaging when indicated

3.      Lumbar puncture

4.      Immediate empiric antimicrobial therapy when bacterial meningitis is suspected

6.2 Giant Cell Arteritis

Age ≥50 years + new headache + scalp tenderness + jaw claudication ± visual symptoms

Evaluate with:

1.      ESR

2.      CRP

3.      CBC

4.      Temporal and axillary artery imaging and/or temporal artery biopsy as appropriate

When suspicion is high, glucocorticoid treatment should not be delayed, particularly when visual symptoms are present.

6.3 Postpartum Headache

Postpartum headache with seizure, focal neurologic deficit, severe hypertension, or thunderclap onset should raise concern for:

1.      CVST

2.      PRES

3.      RCVS

4.      Preeclampsia or eclampsia

6.4 Raised Intracranial Pressure

Papilledema should prompt evaluation for raised intracranial pressure.

Papilledema with pulsatile tinnitus and transient visual obscurations may suggest idiopathic intracranial hypertension (IIH).

Evaluation generally includes:

1.      Brain imaging

2.      Venous imaging

3.      Lumbar puncture with opening pressure when it is safe to perform

6.5 Low CSF Pressure

Headache worse when upright and improved when supine suggests a low CSF pressure syndrome, including spontaneous intracranial hypotension.

6.6 Cervical Artery Dissection

Unilateral head or neck pain + partial Horner syndrome should raise concern for carotid artery dissection.

Urgent vascular imaging with CTA or MRA is appropriate.

6.7 Pituitary Apoplexy

Sudden severe headache + ophthalmoplegia ± visual loss

Consider pituitary apoplexy.

Urgent neuroimaging and endocrine assessment are required.

6.8 Acute Angle-Closure Glaucoma

Severe headache or ocular pain + painful red eye + halos + nausea/vomiting

Consider acute angle-closure glaucoma, an ophthalmic emergency.

7. Primary Headache Phenotypes

Primary headache should be diagnosed only after the clinical presentation has been assessed for concerning secondary causes.

7.1 Migraine Without Aura

Diagnostic features include ≥5 attacks lasting 4 to 72 hours.

At least 2 of the following:

1.      Unilateral location

2.      Pulsating quality

3.      Moderate or severe intensity

4.      Aggravated by or causing avoidance of routine physical activity

Plus at least 1 of:

1.      Nausea and/or vomiting

2.      Photophobia and phonophobia

A patient with a stable, typical migraine pattern and normal neurologic examination generally does not require routine neuroimaging.

7.2 Migraine With Aura

Typical aura symptoms are:

1.      Fully reversible

2.      Often positive phenomena

3.      Develop gradually

4.      May spread or occur sequentially

5.      Individual nonmotor aura symptoms typically last 5 to 60 minutes

6.      Motor aura may last up to 72 hours

Examples include:

1.      Scintillations or flashing lights

2.      Spreading paresthesias

3.      Reversible language symptoms

TIA more often produces sudden negative neurologic symptoms that are maximal at onset, although substantial clinical overlap exists.

7.3 Tension-Type Headache

Typical characteristics include:

1.      Bilateral location

2.      Pressing or tightening quality

3.      Mild to moderate intensity

4.      Not aggravated by routine physical activity

5.      Usually no nausea or vomiting

7.4 Cluster Headache

Typical cluster headache consists of:

1.      At least 5 attacks

2.      Severe or very severe unilateral orbital, supraorbital, or temporal pain

3.      Duration 15 to 180 minutes

4.      Attack frequency from one every other day to eight per day during active periods

5.      Ipsilateral autonomic features such as:

o    Lacrimation

o    Conjunctival injection

o    Nasal congestion or rhinorrhea

o    Eyelid edema

o    Ptosis or miosis

6.      Restlessness or agitation may occur

Acute treatment includes:

1.      High-flow 100% oxygen

2.      A rapid-acting triptan, such as subcutaneous or intranasal therapy, when appropriate

8. Imaging and Lumbar Puncture

8.1 Noncontrast Head CT

Particularly useful for:

1.      Acute intracranial hemorrhage

2.      SAH evaluation

3.      Trauma

4.      Major mass effect

8.2 MRI Brain

Useful when evaluating:

1.      Tumor

2.      Posterior fossa disease

3.      Demyelination

4.      Pituitary pathology

5.      Subtle or subacute intracranial abnormalities

8.3 CTV or MRV

Use when cerebral venous sinus thrombosis is suspected.

8.4 Lumbar Puncture

Important indications include:

1.      Meningitis or encephalitis

2.      Selected patients undergoing SAH evaluation

3.      Measurement of opening pressure

4.      Selected inflammatory or infectious neurologic disorders

When dangerous intracranial mass effect is suspected, assess the patient appropriately before performing LP.

9. Initial Management of Confirmed Aneurysmal SAH

Aneurysmal SAH is a neurologic emergency.

Initial priorities include:

1.      Airway, breathing, and circulation stabilization

2.      Immediate neurologic and neurosurgical or neurointerventional consultation

3.      Appropriate blood pressure monitoring and control, avoiding severe hypertension, hypotension, and large blood pressure variability

4.      Prompt identification and treatment of the ruptured aneurysm, preferably within 24 hours

5.      Endovascular coiling or surgical clipping depending on aneurysm and patient characteristics

6.      Early enteral nimodipine to reduce the risk of delayed cerebral ischemia and improve functional outcome

7.      Monitoring for:

o    Rebleeding

o    Hydrocephalus

o    Delayed cerebral ischemia and vasospasm

o    Seizures

o    Electrolyte and cardiopulmonary complications

10. Common Clinical Traps

1.      “Worst headache means migraine.”

o    A new thunderclap headache requires investigation for secondary causes

2.      “A normal CT excludes every dangerous headache.”

o    False. The diagnostic significance of CT depends on the suspected condition, timing, imaging quality, and clinical context

3.      “A normal neurologic examination excludes SAH.”

o    False

4.      “Papilledema is a feature of migraine.”

o    Papilledema indicates raised intracranial pressure until appropriately evaluated

5.      “Severe hypertension explains the headache.”

o    Evaluate for acute hypertensive target-organ injury and other secondary causes

6.      “Facial pressure means sinus headache.”

o    Migraine commonly produces facial pressure and sinonasal symptoms

11. Rapid Pattern Recognition

Thunderclap headache → SAH / RCVS / CVST / cervical artery dissection

Fever + meningismus → meningitis

Age ≥50 + jaw claudication → giant cell arteritis

Postpartum + seizure → eclampsia / PRES / CVST / RCVS

Papilledema → raised intracranial pressure

Orthostatic headache → low CSF pressure

Head or neck pain + Horner syndrome → carotid artery dissection

Sudden headache + ophthalmoplegia → pituitary apoplexy

Unilateral pulsating headache + nausea + photophobia/phonophobia → migraine

Bilateral pressing or tightening headache → tension-type headache

Severe orbital pain + tearing + restlessness → cluster headache

12. Key Clinical Insight

RED FLAGS FIRST.

A new thunderclap headache should be considered SAH until adequately excluded.

A normal neurologic examination does not exclude SAH.

In an appropriately selected neurologically intact patient, a normal high-quality noncontrast head CT performed within 6 hours can rule out nontraumatic SAH when imaging quality and interpretation are adequate.

At ≥6 hours, with a new neurologic deficit, or when clinical suspicion remains high despite negative CT imaging, further evaluation is required.

A change in headache pattern may be more clinically important than the absolute pain score.

References

1.      Hoh BL, Ko NU, Amin-Hanjani S, et al. 2023 Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage: A Guideline From the American Heart Association/American Stroke Association. Stroke. 2023;54(7):e314-e370. doi:10.1161/STR.0000000000000436.

2.      Godwin SA, Cherkas DS, Panagos PD, et al. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department With Acute Headache. Ann Emerg Med. 2019;74(4):e41-e74. doi:10.1016/j.annemergmed.2019.07.009.

3.      Headache Classification Committee of the International Headache Society. The International Classification of Headache Disorders, 3rd edition. Cephalalgia. 2018;38(1):1-211. doi:10.1177/0333102417738202.