Residency · Residency · Emergency Medicine

Headache Emergencies: Subarachnoid Hemorrhage and Dangerous Mimics

Subarachnoid Hemorrhage

Epidemiology

Subarachnoid hemorrhage has an incidence of 6 to 9 per 100,000 per year, with a mean age of 55 years and a female predominance. Overall mortality is 40 to 50 percent, and 10 to 15 percent of patients die before reaching the hospital. A ruptured saccular (berry) aneurysm accounts for 85 percent of non-traumatic SAH. Risk factors include smoking, hypertension, heavy alcohol use, cocaine use, family history (a first-degree relative with SAH), connective tissue disorders (autosomal dominant polycystic kidney disease, Ehlers-Danlos type IV, and Marfan syndrome), and a history of a prior aneurysm.

Clinical Presentation

The hallmark presentation is a thunderclap headache — sudden-onset, maximal intensity within seconds, often described as the "worst headache of my life." The headache reaches peak intensity within 1 minute in most cases. Associated symptoms include nausea and vomiting (77 percent), neck stiffness (35 percent), loss of consciousness (50 percent), seizure (7 percent), and focal neurologic deficits. A sentinel headache — a warning headache occurring days to weeks before a major rupture — is reported by 20 to 50 percent of patients and is frequently dismissed as migraine or tension headache. Approximately 12 percent of patients presenting to the ED with sudden severe headache have SAH.

Hunt-Hess Classification

The Hunt-Hess classification grades SAH severity. Grade I presents with asymptomatic or mild headache and slight nuchal rigidity. Grade II involves moderate-to-severe headache, nuchal rigidity, and cranial nerve palsy. Grade III presents with drowsiness, confusion, and mild focal deficit. Grade IV involves stupor, moderate-to-severe hemiparesis, and early decerebrate posturing. Grade V presents with deep coma, decerebrate posturing, and moribund appearance. Higher grades carry a worse prognosis.

Diagnostic Approach

CT Head (Non-Contrast)

Non-contrast CT has a sensitivity of 98 to 100 percent within 6 hours of symptom onset when using modern third-generation scanners read by experienced radiologists. Sensitivity drops to 93 percent at 12 hours, 85 percent at 24 hours, and 50 percent at 1 week. The classic pattern shows hyperdense blood in the basal cisterns, sylvian fissures, and interhemispheric fissure. Whether lumbar puncture is still necessary after a negative CT within 6 hours is an active debate — multiple studies demonstrate CT sensitivity approaching 100 percent in this window, leading some to argue that LP can be safely avoided.

Lumbar Puncture

The traditional recommendation is to perform LP if the CT is negative and clinical suspicion remains. Findings of SAH on LP include elevated opening pressure, elevated red blood cells that do not clear between tubes 1 and 4 (though traumatic taps are common and complicate interpretation), and xanthochromia — yellow discoloration of the CSF from bilirubin produced by breakdown of red blood cells. Xanthochromia takes 6 to 12 hours to develop and is the most reliable finding. Visual inspection for xanthochromia is used in most North American centers, while spectrophotometry is more sensitive but not widely available. In distinguishing a traumatic tap from SAH, the ratio of tube 1 to tube 4 RBC count is unreliable. Xanthochromia is the key differentiator — it is present in SAH but absent in a traumatic tap (though if the LP is performed less than 6 hours from symptom onset, xanthochromia may not have developed yet).

CTA

CTA can detect aneurysms 3 mm or larger with greater than 95 percent sensitivity. Some institutions use CT plus CTA as a combined strategy to avoid LP. CTA has false negatives for small aneurysms (less than 3 mm) and may detect incidental aneurysms, which are present in 3 to 5 percent of the general population. The CT plus CTA approach without LP is gaining momentum but is not universally accepted.

Management of Confirmed SAH

Management begins with immediate neurosurgical consultation. Blood pressure is controlled to a target SBP below 160 mmHg (to reduce the risk of rebleeding) using nicardipine or labetalol. The aneurysm is secured via endovascular coiling (preferred for most aneurysms) or surgical clipping. Nimodipine 60 mg orally every 4 hours is administered for 21 days to reduce cerebral vasospasm-related delayed ischemic deficits. Antifibrinolytics (tranexamic acid or aminocaproic acid) may be used short-term before aneurysm securing to reduce rebleeding risk (less than 72 hours). Seizure prophylaxis is controversial — short-term phenytoin or levetiracetam may be used, but prolonged prophylaxis is not recommended. An external ventricular drain is placed for hydrocephalus.

Complications

Rebleeding carries the highest risk in the first 24 hours (4 percent in the first 24 hours) and is devastating, making early aneurysm securing critical. Vasospasm peaks on days 4 through 14 and is monitored with transcranial Doppler. Treatment includes triple-H therapy (hypertension, hypervolemia, and hemodilution) or intra-arterial vasodilators. Hydrocephalus may be acute and obstructive (requiring an EVD) or delayed and communicating (potentially requiring a VP shunt). Hyponatremia is a common complication, and the distinction between cerebral salt wasting (CSW) and SIADH is clinically important: CSW involves volume depletion and is treated with saline, while SIADH involves euvolemia or hypervolemia and is treated with fluid restriction.

Thunderclap Headache Differential

Beyond SAH

The differential for thunderclap headache extends beyond SAH and includes cerebral venous sinus thrombosis (CVST), cervical artery dissection (carotid or vertebral), pituitary apoplexy, reversible cerebral vasoconstriction syndrome (RCVS), posterior reversible encephalopathy syndrome (PRES), spontaneous intracranial hypotension (after LP or from a spontaneous CSF leak), colloid cyst of the third ventricle (positional, causing acute hydrocephalus), hypertensive emergency, and meningitis or encephalitis.

RCVS (Reversible Cerebral Vasoconstriction Syndrome)

RCVS presents with recurrent thunderclap headaches over 1 to 3 weeks, with segmental vasoconstriction visible on CTA or MRA that resolves within 12 weeks. Triggers include the postpartum state and vasoactive drugs (triptans, SSRIs, sympathomimetics, and cannabis). RCVS can cause stroke, hemorrhage, or posterior reversible encephalopathy. Treatment involves a calcium channel blocker (nimodipine or verapamil), trigger avoidance, and supportive care.

Cervical Artery Dissection

Cervical artery dissection presents with sudden headache (often unilateral), neck pain, and Horner syndrome (in carotid dissection) or cranial nerve palsies. It is associated with minor trauma (including chiropractic manipulation and sports) and connective tissue disorders. Diagnosis is made by CTA or MRA with fat-saturated sequences. Treatment involves antithrombotic therapy — the CADISS trial showed no difference between antiplatelets and anticoagulation, and antiplatelets are simpler and preferred by many clinicians.

ED Migraine Management

Acute Migraine Treatment in the ED

First-line treatment is IV prochlorperazine 10 mg (or metoclopramide 10 to 20 mg) combined with IV diphenhydramine 25 mg (to prevent akathisia). Ketorolac 15 to 30 mg IV is added as an adjunct. IV magnesium 2 g is particularly effective for migraine with aura. Dexamethasone 10 mg IV reduces recurrence with a number needed to treat of approximately 9. Opioids should be avoided because they are inferior to the above regimen, promote medication overuse headache, and increase ED recidivism. Sumatriptan 6 mg subcutaneously is effective but should be avoided if there are vascular risk factors or concern for a secondary headache.

Red Flags for Secondary Headache (SNOOP)

The SNOOP mnemonic identifies red flags for secondary headache. S stands for systemic symptoms (fever, weight loss) or systemic disease (HIV, cancer). N stands for neurologic symptoms or signs (focal deficits, seizures, papilledema). O stands for onset that is sudden (thunderclap). The second O stands for older age (new headache after age 50 should prompt consideration of giant cell arteritis). P stands for pattern change, positional component, precipitation by Valsalva, progressive nature, papilledema, or pregnancy and postpartum state.

Giant Cell Arteritis (Temporal Arteritis)

Giant cell arteritis presents with a new headache in a patient over 50 years of age, along with jaw claudication, visual changes (anterior ischemic optic neuropathy), scalp tenderness, and polymyalgia rheumatica symptoms. ESR above 50 and elevated CRP are sensitive but nonspecific. High-dose corticosteroids must be started immediately when clinical suspicion is high — treatment should not wait for biopsy results. Prednisone 60 to 80 mg orally daily is the standard regimen, and IV methylprednisolone 1 g daily for 3 days is used if visual symptoms are present. Temporal artery biopsy should be performed within 2 weeks, as steroids do not alter the pathology for days to weeks.

<image>A CT head image series showing subarachnoid hemorrhage patterns. Image 1: Axial non-contrast CT showing diffuse hyperdense blood in the basal cisterns and sylvian fissures (Fisher grade 3). Image 2: Axial CT showing blood predominantly in the interhemispheric fissure, suggesting an anterior communicating artery aneurysm. Image 3: CTA 3D reconstruction showing a saccular aneurysm at the anterior communicating artery (ACOM). Image 4: A normal CT for comparison. Each image is labeled with anatomical landmarks and arrows highlighting key findings.</image>

<image>A diagnostic algorithm flowchart for the evaluation of suspected SAH. Starting with "Acute thunderclap headache" leading to non-contrast CT head. If CT is positive for SAH, proceed to CTA to identify aneurysm and neurosurgery consultation. If CT is negative and within 6 hours of onset, two pathways are shown: the traditional approach (LP with evaluation for xanthochromia and elevated RBCs) and the emerging approach (CT plus CTA without LP, noting that this is controversial). If beyond 6 hours, LP is recommended as CT sensitivity declines. The flowchart includes decision points for positive and negative LP results, with next steps for each. A controversy box highlights the debate over LP necessity after a negative CT within 6 hours.</image>

<image>A table-format illustration comparing the thunderclap headache differential diagnosis. For each condition (SAH, RCVS, cervical artery dissection, CVST, pituitary apoplexy, and colloid cyst), the image shows: typical presentation features, key diagnostic test, characteristic imaging findings, and initial treatment. Each condition is color-coded and arranged in rows for rapid comparison.</image>

Clinical Pearls

Modern CT sensitivity for SAH approaches 100 percent within 6 hours, and the debate over whether LP is still necessary in this window is active and shifting practice. Sentinel headaches occur in 20 to 50 percent of SAH patients before a major rupture, and any sudden severe headache warrants serious evaluation. Xanthochromia takes 6 to 12 hours to develop, so an LP performed too early after symptom onset may miss this finding. Nimodipine is the only calcium channel blocker shown to improve outcomes in SAH — it reduces vasospasm-related deficits rather than vasospasm itself. Opioids should be avoided for ED migraine treatment because prochlorperazine plus diphenhydramine plus ketorolac is superior and evidence-based. Giant cell arteritis demands immediate steroid initiation when suspected — vision loss is preventable but irreversible once established. Cervical artery dissection should always be considered in young patients with sudden headache and neck pain, especially when Horner syndrome is present.

References

• Perry JJ, et al. Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage. BMJ. 2011;343:d4277.
• Connolly ES, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage. Stroke. 2012;43:1711-1737.
• Friedman BW, et al. Randomized trial of IV prochlorperazine plus diphenhydramine vs. IV hydromorphone for migraine. Neurology. 2017;89:2075-2082.
• Blok KM, et al. CT within 6 hours of headache onset to rule out subarachnoid hemorrhage: noninferiority study. Neurology. 2015;84:1927-1932.
• Markus HS, et al. Antiplatelet therapy vs anticoagulation therapy in cervical artery dissection (CADISS). Lancet Neurol. 2015;14:361-367.

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