What is the hallmark feature of the headache associated with subarachnoid hemorrhage?

Characteristic Feature of Subarachnoid Hemorrhage Headache

The hallmark feature of subarachnoid hemorrhage headache is severe pain with sudden onset reaching maximum intensity within one minute, classically described as "the worst headache of my life" and reported by 80% of patients who can provide history. 1, 2

Key Clinical Features

Thunderclap Onset Pattern

• The defining characteristic is a "thunderclap headache" with instantly peaking pain reaching maximum severity within 60 seconds. 1
• This rapid onset to peak intensity distinguishes SAH from other headache types that develop gradually over hours or days. 1
• The 2023 AHA/ASA guidelines specifically identify "thunderclap headache (instantly peaking pain)" as one of the six Ottawa SAH Rule criteria requiring additional investigation. 1

Pain Severity

• The American Stroke Association reports that 80% of SAH patients describe their headache as "the worst headache of my life." 2, 3, 4
• This severe intensity is a critical distinguishing feature, though the 2023 guidelines note that ruptured aneurysms can occasionally present with milder symptoms (Hunt and Hess Grade 1). 2

Associated Features (Not Defining)

• Neck pain or stiffness occurs commonly but is not the primary defining feature. 1
• Onset during exertion is a risk factor included in the Ottawa SAH Rule but not universal. 1
• Nausea, vomiting, and photophobia frequently accompany SAH headache. 4

What SAH Headache Is NOT

Excluded Characteristics

• NOT associated with fever and jaw claudication - these features suggest temporal arteritis, not SAH. 1
• NOT intermittent and unilateral in the temporal area - this pattern is more consistent with migraine or cluster headache. 5
• NOT gradual onset over several days - SAH headache reaches peak intensity within one minute by definition. 1

Clinical Decision-Making

Ottawa SAH Rule Application

The 2023 AHA/ASA guidelines recommend using the Ottawa SAH Rule for alert patients >15 years with new severe nontraumatic headache reaching maximum intensity within 1 hour. Investigation is required if ANY of these criteria are met: 1

• Age ≥40 years
• Neck pain or stiffness
• Witnessed loss of consciousness
• Onset during exertion
• Thunderclap headache (instantly peaking pain)
• Limited neck flexion on examination

Diagnostic Approach

• Non-contrast head CT within 6 hours of symptom onset has 98.7% sensitivity and can miss <1.5 in 1000 SAHs. 1
• If CT is negative but clinical suspicion remains high (especially if presenting >6 hours from onset), lumbar puncture for xanthochromia evaluation is mandatory. 1

Critical Pitfall to Avoid

Misdiagnosis of aneurysmal SAH occurs in up to 12% of cases, with failure to obtain neuroimaging being the most common error. 2 The sudden, severe, "thunderclap" nature of the headache reaching peak intensity within one minute is the single most important clinical feature that should trigger immediate investigation, as missing this diagnosis carries nearly 4-fold higher likelihood of death or disability. 2