Residency · Residency · Neurology

Subarachnoid Hemorrhage for the Neurologist

Overview

Aneurysmal subarachnoid hemorrhage (aSAH) accounts for roughly 5% of all strokes but disproportionately strikes younger patients, with a mean age of about 55. Despite its relative rarity, the consequences are devastating: mortality is approximately 30-40%, and one-third of survivors live with significant disability. The major cause of secondary morbidity after the initial bleed is delayed cerebral ischemia (DCI) resulting from vasospasm. The neurologist plays a critical role throughout the course of this disease, from initial diagnosis through neurological monitoring and management of the many complications that follow.

Etiology

The overwhelming majority of non-traumatic SAH, about 85%, results from a ruptured intracranial aneurysm. The most common locations are the anterior communicating artery (30%), the posterior communicating artery (25%), and the MCA bifurcation (20%). Risk factors for aneurysm formation and rupture include hypertension, smoking, family history of aneurysmal disease, connective tissue disorders (particularly Ehlers-Danlos type IV and autosomal dominant polycystic kidney disease), and female sex. Non-aneurysmal perimesencephalic SAH accounts for roughly 10% of cases and carries a benign prognosis, with blood characteristically centered around the brainstem. Other causes include arteriovenous malformations, dural arteriovenous fistulae, dissection, vasculitis, coagulopathy, and reversible cerebral vasoconstriction syndrome.

Clinical Presentation

The hallmark presentation is the "worst headache of my life," sudden in onset and maximal at its very beginning, the classic thunderclap headache. Accompanying symptoms typically include nausea, vomiting, photophobia, and neck stiffness from meningismus. Loss of consciousness at onset occurs in approximately 50% of patients. Focal neurological deficits depend on the aneurysm location; a posterior communicating artery aneurysm, for instance, classically presents with a CN III palsy. Seizures occur at onset in about 10% of cases. A sentinel headache, representing a warning leak, is reported in 10-40% of patients in the days to weeks preceding frank rupture.

Diagnosis

Imaging

Non-contrast CT of the head is the initial study of choice, with sensitivity approaching 98% within the first 6 hours of symptom onset. This sensitivity declines to roughly 93% at 24 hours and drops to approximately 50% at one week, making timing critical. CT angiography identifies aneurysm location, size, and morphology with sensitivity exceeding 98% for aneurysms 3 mm or larger. Lumbar puncture is required when the CT is negative but clinical suspicion remains high; the diagnostic findings are xanthochromia (by visual inspection or spectrophotometry) and an elevated red blood cell count that does not clear between tubes 1 and 4. Digital subtraction angiography (DSA) remains the gold standard for aneurysm detection and is required when CTA is negative but SAH has been confirmed on CT or LP.

Grading Scales

Hunt-Hess Scale

The Hunt-Hess scale grades clinical severity from I to V. Grade I denotes asymptomatic or mild headache with slight nuchal rigidity. Grade II involves moderate to severe headache and nuchal rigidity without neurological deficit other than a possible cranial nerve palsy. Grade III includes drowsiness, confusion, or a mild focal deficit. Grade IV presents with stupor, moderate to severe hemiparesis, or early decerebrate rigidity. Grade V describes deep coma with decerebrate rigidity and a moribund appearance.

World Federation of Neurosurgical Societies (WFNS)

The WFNS scale is based on the Glasgow Coma Scale and the presence of focal deficits. Grade I corresponds to GCS 15, Grade II to GCS 13-14 without focal deficit, Grade III to GCS 13-14 with a focal deficit, Grade IV to GCS 7-12, and Grade V to GCS 3-6.

Modified Fisher Scale (CT pattern)

The Modified Fisher Scale predicts the risk of vasospasm and DCI based on the CT appearance. Grade 0 indicates no SAH or intraventricular hemorrhage (IVH). Grade 1 shows thin SAH without IVH. Grade 2 shows thin SAH with IVH. Grade 3 reveals thick SAH without IVH. Grade 4 demonstrates thick SAH with IVH. Higher grades predict a correspondingly higher risk of vasospasm and DCI.

Aneurysm Securing

Surgical Clipping vs Endovascular Coiling

The landmark ISAT trial (2002, with updated data through 2015) demonstrated that endovascular coiling is superior to surgical clipping for ruptured aneurysms suitable for either approach, showing lower rates of 1-year dependency and death. Although coiling carries a higher rebleeding rate, the overall net benefit was maintained at 18-year follow-up. Coiling is generally preferred when anatomy is favorable, particularly for posterior circulation aneurysms and in elderly patients. Clipping remains preferred for MCA aneurysms, wide-necked aneurysms, aneurysms with important branch vessels arising from the dome, and situations where mass effect requires decompression. Early securing within 24 hours is recommended to prevent rebleeding.

Flow Diversion

Pipeline embolization devices and other flow diverters are used for select unruptured and some ruptured aneurysms. These devices create endoluminal reconstruction of the parent artery, causing the aneurysm to thrombose over weeks to months. Because they require dual antiplatelet therapy, their use in acute SAH is limited.

Neurological Complications

Rebleeding

The risk of rebleeding is highest in the first 24 hours, at roughly 4% on the first day and 1-2% per day for the first two weeks. Prevention strategies include early aneurysm securing, blood pressure control (targeting systolic pressure below 160 mmHg before securing), bed rest, and anti-fibrinolytic agents such as tranexamic acid as a bridge to definitive treatment, though these should be limited to fewer than 72 hours. The ULTRA trial showed a trend toward benefit with short-course tranexamic acid.

Vasospasm and Delayed Cerebral Ischemia (DCI)

Vasospasm refers to angiographic narrowing of cerebral arteries that typically occurs between days 3 and 14, peaking around days 7-10. DCI is the clinical correlate: a new focal deficit or decreased consciousness attributable to ischemia from vasospasm or related mechanisms, occurring in approximately 30% of aSAH patients. Nimodipine, a calcium channel blocker given at 60 mg orally or via nasogastric tube every 4 hours for 21 days, is the only pharmacologic intervention proven to improve outcomes. Notably, nimodipine reduces DCI and improves neurological outcomes without reducing angiographic vasospasm itself. Monitoring relies on serial neurological examinations (the most sensitive method), transcranial Doppler (where MCA velocity above 200 cm/s or a Lindegaard ratio greater than 6 suggests severe vasospasm), CTA, and CT perfusion. Treatment of established DCI centers on induced hypertension through vasopressor augmentation and maintenance of euvolemia. The historical "triple H therapy" is outdated; hypertension is the key intervention, and hypovolemia must be avoided. Endovascular rescue with intra-arterial vasodilators or balloon angioplasty is reserved for refractory cases.

Hydrocephalus

Acute hydrocephalus develops within hours to days and may be obstructive (from IVH) or communicating (from blood in the cisterns); it is treated with an external ventricular drain. Chronic communicating hydrocephalus develops over weeks to months from impaired CSF absorption, and approximately 20% of patients ultimately require a permanent ventriculoperitoneal shunt. Risk factors include thick SAH, IVH, older age, and poor clinical grade.

Seizures

Seizures occur at onset in about 10% of patients, with delayed seizures developing in an additional 5-10%. Prophylactic antiseizure medication remains controversial; the AHA/ASA suggests that short-term prophylaxis may be considered. Phenytoin is specifically associated with worse cognitive outcomes in SAH patients and should be avoided; levetiracetam is the preferred agent if prophylaxis is warranted. Continuous EEG monitoring should be considered for patients with poor-grade SAH or unexplained neurological deterioration.

Cardiac Complications

Neurogenic stunned myocardium produces wall motion abnormalities, troponin elevation, and ECG changes including deep T-wave inversions, ST-segment changes, and QT prolongation, all driven by a massive catecholamine surge. Takotsubo (stress) cardiomyopathy with apical ballooning is a related phenomenon that is usually reversible. Arrhythmias warrant continuous telemetry monitoring. These cardiac complications may limit the ability to use induced hypertension for DCI treatment.

Hyponatremia

Hyponatremia affects approximately 30% of aSAH patients. Cerebral salt wasting (CSW) produces hyponatremia with volume depletion and natriuresis, treated with isotonic or hypertonic saline and fludrocortisone. SIADH produces hyponatremia with euvolemia or mild hypervolemia, but fluid restriction is dangerous in SAH because it risks worsening hypovolemia and increasing DCI. Distinguishing CSW from SIADH depends on assessment of volume status; when uncertain, volume repletion is the safer approach. Rapid sodium correction must be avoided due to the risk of osmotic demyelination.

<image>A comprehensive clinical timeline of subarachnoid hemorrhage management from ictus through day 21. The timeline shows key events and interventions: Day 0 (presentation, CT/CTA, grading, resuscitation, start nimodipine), Day 0-1 (aneurysm securing by coiling or clipping), Days 1-3 (monitor for rebleeding, manage hydrocephalus with EVD if needed), Days 3-14 (vasospasm window: daily TCD monitoring, neurological checks, treat DCI with induced hypertension and endovascular rescue if needed), Days 14-21 (weaning nimodipine, assess for chronic hydrocephalus, shunt evaluation), and beyond (cognitive rehabilitation, screening of family members). Complication risks (rebleeding, vasospasm/DCI, hydrocephalus, seizures, cardiac, hyponatremia) are plotted as overlapping curves showing when each peaks.</image>

<image>A diagnostic imaging panel for SAH. Panel A: non-contrast CT showing thick SAH in the basal cisterns (modified Fisher grade 3-4). Panel B: CT angiography with 3D reconstruction showing an anterior communicating artery aneurysm. Panel C: digital subtraction angiography (DSA) confirming the aneurysm. Panel D: post-coiling DSA showing successful aneurysm occlusion. Panel E: transcranial Doppler schematic showing the probe positions and an example waveform with elevated MCA velocity indicating vasospasm.</image>

Clinical Pearls

Any sudden-onset thunderclap headache that is maximal at onset demands evaluation for SAH, even when the CT is negative; a lumbar puncture is required to exclude the diagnosis. CT sensitivity for SAH drops significantly after 6-12 hours, so a "negative CT" obtained after a delay cannot be trusted to rule out the condition. Nimodipine is the only pharmacologic intervention proven to improve outcomes in aSAH, and its mechanism is reduction of DCI rather than reduction of angiographic vasospasm. Phenytoin is associated with worse cognitive outcomes in SAH and should be replaced by levetiracetam when seizure prophylaxis is indicated. Hyponatremia in SAH is more commonly due to cerebral salt wasting than SIADH, and fluid restriction can be dangerous because it worsens hypovolemia and increases DCI risk. A new CN III palsy accompanied by headache should immediately raise concern for posterior communicating artery aneurysm rupture or expansion. Early aneurysm securing within 24 hours remains the single most important intervention to prevent rebleeding.

References

• Connolly ES, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage. Stroke. 2012;43(6):1711-1737.
• Molyneux AJ, et al. International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling: long-term follow-up. Lancet Neurol. 2015;14(12):1121-1131.
• Diringer MN, et al. Critical care management of patients following aneurysmal subarachnoid hemorrhage. Neurocrit Care. 2011;15(2):211-240.
• Pickard JD, et al. Effect of oral nimodipine on cerebral infarction and outcome after subarachnoid haemorrhage. BMJ. 1989;298(6674):636-642.
• Vergouwen MD, et al. Definition of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage. Stroke. 2010;41(10):2391-2395.

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