Subarachnoid haemorrhage is a devastating cerebrovascular emergency defined by the accumulation of blood within the subarachnoid space, the fluid-filled compartment situated between the arachnoid mater and the pia mater of the central nervous system 1,2. Although it accounts for approximately 5% of all stroke cases, its impact is disproportionately severe because it typically strikes individuals in the prime of life, with a mean age of onset in the mid-fifties 2,4,5. The condition carries a formidable burden of morbidity and mortality, with roughly one-quarter of patients dying before reaching a medical facility and overall case fatality rates approaching 40% to 50% among those hospitalized 2,5. Prompt clinical recognition, rigorous diagnostic evaluation, and specialized multidisciplinary care within neurosurgical intensive care units are vital to alter the natural history of this catastrophic condition 3,6.
1. Etiology & Risk Factors
- Aneurysmal Rupture: Approximately 85% of spontaneous subarachnoid haemorrhages are caused by the rupture of an intracranial saccular (berry) aneurysm 4,5. These thin-walled out pouchings typically develop at bifurcations of the major cerebral arteries located within the circle of Willis and anterior circulation 1.
- Anatomical Distribution: The most common site for intracranial saccular aneurysms is the anterior communicating artery (30–38%), followed by the middle cerebral artery bifurcation (20%), the junction of the internal carotid artery and the posterior communicating artery (25%), and the basilar artery apex (10%) 1.
- Non-Aneurysmal Perimesencephalic Haemorrhage: Accounts for about 10% of cases, where blood is restricted to the perimesencephalic and prepontine cisterns without an identifiable vascular lesion on initial or repeat angiography; this variant carries an exceptionally benign prognosis with a very low risk of rebleeding or delayed ischaemia 1.
- Vascular Malformations: Less common etiologies include arteriovenous malformations (AVMs), dural arteriovenous fistulas, mycotic aneurysms, and arterial dissections 1.
- Modifiable Risk Factors: Cigarette smoking, chronic hypertension, heavy alcohol consumption, and sympathomimetic drug abuse (such as cocaine or amphetamines) significantly increase both the formation and rupture risk of intracranial aneurysms 1,2.
- Non-Modifiable and Genetic Risk Factors: Female sex (post-menopausal), older age, and family history of intracranial aneurysms or subarachnoid haemorrhage 1. Autosomal dominant polycystic kidney disease (ADPKD), Ehlers-Danlos syndrome type IV, Marfan syndrome, and pseudoxanthoma elasticum are well-established heritable connective tissue disorders predisposing to aneurysm formation 1.
2. Pathophysiology
The pathophysiological trajectory of subarachnoid haemorrhage unfolds across multiple phases, starting with the mechanical disruption of the vessel wall and culminating in complex secondary brain injury cascades 1,6. Under normal physiological conditions, intracranial saccular aneurysms develop at arterial bifurcations due to congenital or acquired defects in the internal elastic lamina and media layer of the vessel wall, subjected to continuous hemodynamic wall shear stress 1. Upon wall failure, high-pressure arterial blood surges directly into the subarachnoid space 1,5. This abrupt extravasation causes an immediate and dramatic spike in intracranial pressure (ICP), which frequently matches or exceeds mean arterial pressure, transiently arresting cerebral blood flow and accounting for the transient loss of consciousness observed at onset in up to half of patients 1.
Following initial stabilization, the presence of blood breakdown products in the subarachnoid space initiates a profound neuroinflammatory response and localized vasospasm 1,6. Erythrocytes lyse, releasing oxyhemoglobin into the cerebrospinal fluid, which generates reactive oxygen species, induces lipid peroxidation, and causes direct endothelial injury 1. This biochemical cascade leads to sustained smooth muscle contraction in large conductive cerebral arteries, manifesting clinically as delayed cerebral ischaemia (DCI) between days 4 and 14 post-ictus 1,3,5. Furthermore, acute obstruction of arachnoid granulations by blood clots impedes cerebrospinal fluid reabsorption, precipitating acute communicating hydrocephalus, while early brain injury (EBI) mechanisms—comprising global cerebral ischemia, blood-brain barrier disruption, and cerebral edema—compound the initial neuronal damage within the first 72 hours 1,6.
3. Clinical Presentation & Classic Clinical Signs
- History & Cardinal Symptoms: The hallmark manifestation of subarachnoid haemorrhage is a hyperacute, excruciating headache classically described by the patient as the "worst headache of my life" or a "thunderclap headache," which reaches maximal intensity within seconds to less than five minutes 1,2,5. This headache may be accompanied by nausea, projectile vomiting, photophobia, and neck stiffness reflecting meningeal irritation 1,2. A sentinel headache—a milder warning headache occurring days to weeks prior to major rupture—is reported by 10% to 43% of patients and represents a minor leakage or expansion of the aneurysm 1.
- Physical Examination & Named Clinical Signs:
- Meningism: Neck stiffness (nuchal rigidity) and positive Kernig's and Brudzinski's signs typically develop within 6 to 12 hours as blood tracks into the spinal subarachnoid space and irritates the meninges 1.
- Neurological Deficits: Focal neurological signs may manifest depending on the exact location of the ruptured aneurysm and the resulting hematoma 2. A third cranial nerve (CN III) palsy characterized by an ipsilateral dilated pupil with loss of the light reflex, ptosis, and "down and out" eye deviation strongly points to a posterior communicating artery aneurysm 1. Sixth cranial nerve palsies, unilateral weakness, or aphasia may also occur 2.
- Alteration of Consciousness: Patients may present with anything from mild lethargy and confusion to deep coma, depending on the severity of the initial bleed and secondary intracranial pressure elevation 2,5. Subhyaloid retinal haemorrhages (Terson syndrome) can occur due to acute intracranial pressure transmission down the optic nerve sheath 1.
4. Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)
| Diagnostic Modality / Test | Expected Clinical & Radiological / Laboratory Finding |
|---|---|
| Gold-Standard Investigation | Non-contrast head computed tomography (NCCT) performed within 6 hours of symptom onset demonstrates a sensitivity exceeding 98.5%, displaying hyperdense blood pooling within the basal cisterns, Sylvian fissures, and interhemispheric fissure 1. |
| Laboratory Panel & CSF Analysis | If NCCT is negative and performed >6 hours post-onset, diagnostic lumbar puncture (LP) is mandatory 1,5. LP reveals uniformly blood-stained cerebrospinal fluid across sequential tubes without clearing (distinguishing true haemorrhage from a traumatic tap) and cerebrospinal fluid spectrophotometry demonstrating bilirubin xanthochromia (yellow discoloration due to oxyhemoglobin breakdown), which typically appears after 12 hours 1. Complete blood count, coagulation profile, and serum electrolytes (monitoring for hyponatremia from cerebral salt-wasting syndrome) are essential 1,3. |
| Imaging / Radiology (X-ray, US, CT, MRI) | CT angiography (CTA) is the first-line vascular imaging modality used to delineate the size, shape, and anatomical relationship of the intracranial aneurysm 1. Digital subtraction angiography (DSA) remains the gold standard for vascular anatomy, offering superior spatial resolution to detect small aneurysms (<3 mm) or complex angioarchitecture when CTA is equivocal 1. Transcranial Doppler (TCD) ultrasound is utilized serially to monitor cerebral blood flow velocities and screen for vasospasm 3. |
| ECG / Histopathology / Procedural | Electrocardiogram frequently shows non-specific ST-segment elevations or depressions, deep symmetrical T-wave inversions ("cerebral T-waves"), and QT prolongation due to a massive catecholamine surge induced by acute intracranial catastrophe 1. Cardiac troponin release may also occur mimicking acute myocardial infarction (neurogenic stunned myocardium) 1. |
5. Staging, Classification & Clinical Scoring Systems
| Criterion / Stage / Score Component | Clinical Threshold, Points & Management Implication |
|---|---|
| Hunt and Hess Scale | Grade I: Asymptomatic or minimal headache and slight nuchal rigidity. Grade II: Moderate-to-severe headache, nuchal rigidity, no neurological deficit except cranial nerve palsy. Grade III: Drowsiness, confusion, or mild focal deficit. Grade IV: Stupor, moderate-to-severe hemiparesis. Grade V: Deep coma, decerebrate rigidity, moribund appearance. Higher grades correlate directly with increased surgical morbidity and mortality 1. |
| World Federation of Neurosurgical Societies (WFNS) Scale | Grade 1: GCS 15, no motor deficit. Grade 2: GCS 13–14, no motor deficit. Grade 3: GCS 13–14, with motor deficit. Grade 4: GCS 7–12, with or without motor deficit. Grade 5: GCS 3–6, with or without motor deficit. Widely utilized for objective neurological grading based on the Glasgow Coma Scale 1. |
| Fisher Scale (Original) | Grade 1: No blood detected on CT. Grade 2: Diffuse thin blood or local clot <1 mm thick in vertical cisterns. Grade 3: Localized clot and/or vertical layer of blood ≥1 mm thick. Grade 4: Diffuse or no subarachnoid blood, but intracerebral or intraventricular clot present. Grade 3 and 4 confer the highest risk for developing delayed cerebral ischaemia (vasospasm) 1. |
6. Differential Diagnosis
| Differential Condition | Distinguishing Clinical, Biochemical & Imaging Features |
|---|---|
| Migraine (with or without aura / Thunderclap variant) | History of recurrent, throbbing headaches with migrainous features (nausea, photophobia, aura); neuroimaging is completely normal, and cerebrospinal fluid analysis shows no red blood cells or xanthochromia 1. |
| Primary Thunderclap Headache (Benign) | Sudden onset thunderclap headache mimicking subarachnoid haemorrhage, but non-contrast head CT and lumbar puncture are entirely normal; headache resolves spontaneously or with analgesics without structural vascular pathology 1. |
| Cerebral Venous Sinus Thrombosis (CVST) | Subacute or sudden headache accompanied by signs of intracranial hypertension (papilledema, visual changes, focal seizures); non-contrast head CT may show the dense triangle sign, but magnetic resonance venography (MRV) or CT venography (CTV) confirms venous sinus occlusion 1. |
| Reversible Cerebral Vasoconstriction Syndrome (RCVS) | Characterized by recurrent thunderclap headaches triggered by exertion, emotional stress, or valsalva, often associated with postpartum state or vasoactive drug exposure; neuroimaging shows characteristic multifocal segmental cerebral arterial constriction that resolves spontaneously within 12 weeks 1. |
| Meningitis / Encephalitis | Fever, altered mental status, and meningism developing subacutely over days rather than hyperacutely within seconds; cerebrospinal fluid analysis reveals marked pleocytosis (predominantly neutrophilic or lymphocytic), elevated protein, and low glucose, without xanthochromia 1. |
7. Management & Treatment Protocol
- Initial Stabilization & Resuscitation: Patients presenting with suspected subarachnoid haemorrhage require immediate admission to a dedicated neurosurgical intensive care unit 3,7. Airway protection via endotracheal intubation is mandatory for patients with depressed consciousness (GCS <8). Strict hemodynamic monitoring and arterial line placement are established to maintain cerebral perfusion pressure (CPP = MAP - ICP) 3. Blood pressure must be meticulously managed prior to aneurysm securement, targeting a systolic blood pressure <160 mmHg (or mean arterial pressure <110 mmHg) using titratable intravenous antihypertensive infusions (e.g., nicardipine or labetalol) to minimize the risk of rebleeding while maintaining adequate cerebral perfusion 1,5.
- First-Line Medical & Pharmacological Therapy:
- Nimodipine: Administered orally (or via nasogastric tube) at a dose of 60 mg every 4 hours for 21 consecutive days to all patients with aneurysmal subarachnoid haemorrhage to reduce the incidence and severity of delayed cerebral ischaemia and poor neurological outcomes 1,4,5. If systemic hypotension limits administration, the dose may be reduced to 30 mg every 2 hours, but treatment should not be prematurely discontinued 1.
- Fluid and Electrolyte Management: Euvolemia must be strictly maintained; prophylactic hypervolemia is no longer recommended. Fluid restriction is strictly avoided as it exacerbates vasospasm and delayed cerebral ischaemia 1,5. Hyponatremia—frequently caused by cerebral salt-wasting syndrome—should be aggressively managed with isotonic saline infusions and fludrocortisone or hypertonic saline, avoiding free water restriction to prevent intravascular volume depletion 1,3.
- Seizure Prophylaxis and Analgesia: Short-term prophylactic anticonvulsants (e.g., levetiracetam) may be utilized in the perioperative period, though routine long-term use is not indicated 1. Adequate analgesia and sedation are maintained to prevent blood pressure surges 1.
- Surgical / Interventional Indications:
- Timing of Aneurysm Securement: To prevent the catastrophic risk of rebleeding—which carries a mortality rate exceeding 70%—the ruptured aneurysm must be secured as early as possible, ideally within 24 to 72 hours of ictus 1,5,6.
- Endovascular Coiling vs. Microsurgical Clipping: Endovascular obliteration via detachable platinum coils is the preferred primary modality for most ruptured aneurysms due to lower procedural morbidity and improved clinical outcomes at one year, provided the aneurysm geometry is favorable 1,5. Microsurgical clipping is indicated for aneurysms with a wide neck, unfavorable dome-to-neck ratios, associated large intracerebral hematomas requiring surgical evacuation, or when endovascular access is anatomically constrained 1,5. External ventricular drainage (EVD) or lumbar drain placement is performed urgently for patients developing symptomatic acute hydrocephalus or elevated intracranial pressure 1,5.
8. Complications & Prognosis
- Rebleeding: The most feared acute complication, occurring most frequently within the first 24 hours (with a peak risk in the first few hours). Rebleeding carries a dismal mortality rate of 70% to 80%, underscoring the critical imperative for urgent aneurysm securement and strict blood pressure control 1,5.
- Delayed Cerebral Ischaemia (DCI) & Vasospasm: Manifests as clinical deterioration (new focal deficits, confusion, or decline in consciousness) typically between days 4 and 14 following the initial hemorrhage, driven by large-vessel arterial narrowing and microvascular dysfunction 1,3. Management includes induced arterial hypertension (using vasopressors such as phenylephrine or norepinephrine), maintenance of euvolemia, and urgent rescue therapy via endovascular balloon angioplasty or intra-arterial vasodilators (e.g., nicardipine or verapamil) for refractory cases 1.
- Hydrocephalus: Acute communicating hydrocephalus develops in 20% to 30% of patients due to blood obstructing cerebrospinal fluid pathways, requiring temporary external ventricular drainage or lumbar drainage 1,5. Chronic normal pressure hydrocephalus may develop weeks later, requiring permanent ventriculoperitoneal shunting 1.
- Systemic Complications: Neurogenic pulmonary edema, cardiac arrhythmias, myocardial stunning, and severe hyponatremia due to cerebral salt-wasting or syndrome of inappropriate antidiuretic hormone secretion (SIADH) frequently complicate the intensive care course and require aggressive multidisciplinary management 1,3.
- Prognosis: Despite advancements in endovascular techniques and neurocritical care, aneurysmal subarachnoid haemorrhage maintains a high overall mortality rate of approximately 40% to 50% 1,5. Among survivors, long-term neuropsychiatric sequelae—including cognitive impairment, fatigue, emotional lability, depression, and reduced quality of life—are prevalent and necessitate comprehensive rehabilitation programs 2,4.
