What is the red flag sign in subarachnoid hemorrhage?

Red Flag Signs in Subarachnoid Hemorrhage

The cardinal red flag sign in subarachnoid hemorrhage is sudden-onset, severe headache reaching maximal intensity within seconds to minutes, classically described as "the worst headache of my life" by 80% of patients who can provide a history. 1, 2, 3

Primary Clinical Red Flags

The Sentinel Headache Pattern

• Sudden onset with peak intensity immediately or within 1 hour distinguishes SAH from other headache types and is present in 74% of confirmed cases 1
• The headache reaches maximum severity within seconds to minutes, not gradually over hours or days 1, 4
• Sentinel or "warning" headaches occur in 10-43% of patients within 2-8 weeks before major rupture, and dismissing these increases the odds of early rebleeding 10-fold 2

Associated Neurological Red Flags

• Brief loss of consciousness occurs in 53% of cases and signals significant hemorrhage 1
• Nuchal rigidity or neck stiffness is present in 35% of cases 1, 5
• Nausea and/or vomiting accompanies the headache in 77% of cases 1
• Focal neurological deficits including cranial nerve palsies should never be dismissed as "simple headache" and mandate immediate neuroimaging 2
• Photophobia is a common accompanying symptom 1, 5

Critical Timing Considerations

Immediate Mortality Risk

• The risk of recurrent hemorrhage is greatest in the hours immediately after initial hemorrhage, with mortality rates of 70-90% 6
• The rebleeding rate in the first 24 hours is 3-4%, representing the highest risk period 1, 2
• One in eight patients with SAH dies outside the hospital before reaching medical care 4

Diagnostic Window

• CT sensitivity is close to 100% in the first 3 days after SAH but declines to 93% at 24 hours and 57-85% at 6 days 1
• If CT is negative but clinical suspicion remains high based on red flag features, lumbar puncture must be performed to evaluate for xanthochromia, which has 100% sensitivity and 95.2% specificity when performed >6-12 hours after symptom onset 1, 2

Common Diagnostic Pitfalls

Misdiagnosis Patterns

• Misdiagnosis of aneurysmal SAH occurs in up to 12% of cases, with failure to obtain neuroimaging being the most common error 2
• Misdiagnosis carries a nearly 4-fold higher likelihood of death or disability 2
• Failure to recognize progressive worsening over weeks, change in personality or cognition, and sudden onset of focal neurological deficit leads to missed diagnoses 2

Atypical Presentations

• Ruptured aneurysms can occasionally present with less dramatic symptoms, including mild headache (Hunt and Hess Grade 1), meaning even ruptured aneurysms may present with subtle findings 2
• Not all patients will describe their headache as "the worst of my life," but the sudden onset and maximal intensity within minutes remains the distinguishing feature 1, 4

Immediate Management Priorities

Blood Pressure Control

• Systolic blood pressure must be maintained below 160 mmHg using titratable agents (nicardipine, labetalol, or clevidipine) to prevent rebleeding 1, 3
• Avoid measures that rapidly lower intracranial pressure, as this increases the likelihood of rebleeding 5

Urgent Intervention

• Early neurosurgical or endovascular intervention is critical to prevent rebleeding, with patients achieving better functional outcomes when treatment occurs within 3 days versus delayed >14 days 6, 2
• Transfer to high-volume centers (>35 aSAH cases/year) improves outcomes 2