Subarachnoid Hemorrhage from Ruptured Aneurysm
A headache described as "worst headache of my life" is most likely subarachnoid hemorrhage (SAH) from a ruptured cerebral aneurysm until proven otherwise. This classic presentation occurs in approximately 80% of patients with aneurysmal SAH who can provide a history 1, 2.
Why This Diagnosis Takes Priority
The mortality from aneurysmal SAH exceeds 30%, with only 30% of patients recovering sufficiently for independent living, making immediate recognition and treatment critical 3. The American Heart Association emphasizes that this presentation—characterized by sudden-onset severe headache reaching maximal intensity immediately (thunderclap headache)—is the hallmark clinical feature 1, 2.
Key Distinguishing Features
- Onset characteristics: The headache reaches peak intensity within seconds to minutes, not gradually over hours 1, 4
- Severity: Patients consistently describe this as distinctly different from any prior headache 1
- Associated symptoms: Nausea/vomiting (77%), brief loss of consciousness (53%), neck stiffness (35%), and photophobia commonly accompany the headache 1
Critical Diagnostic Pathway
Immediate Imaging (Within Minutes)
Non-contrast head CT must be obtained immediately and has 98-100% sensitivity when performed within the first 12 hours after symptom onset 1, 2. The sensitivity decreases to 93% at 24 hours and 57-85% by day 6 1.
If CT is Negative
Lumbar puncture is mandatory when CT is negative but clinical suspicion remains high 1, 2. The cerebrospinal fluid should be analyzed for xanthochromia, which has nearly 100% sensitivity when performed >6-12 hours after symptom onset 2. The most common diagnostic error leading to misdiagnosis is failure to obtain neuroimaging, occurring in up to 12% of cases 1, 5.
Vascular Imaging
Once SAH is confirmed, CTA head or catheter angiography is required to identify the bleeding source, with catheter angiography demonstrating >98% sensitivity and specificity for detecting aneurysms 1.
Why Misdiagnosis is Catastrophic
Misdiagnosis or delayed diagnosis is associated with a nearly 4-fold higher likelihood of death or disability at 1 year 1. The risk of rebleeding is 3-4% in the first 24 hours and 1-2% per day in the first month, with rebleeding carrying extremely high mortality 1, 5.
Warning/Sentinel Headaches
10-43% of patients report a warning or sentinel headache within 2-8 weeks before major rupture, which increases the odds of early rebleeding 10-fold if missed 1, 5. These sentinel headaches are typically milder but last several days and should prompt immediate evaluation 1.
Alternative Diagnoses to Consider (But Not Prioritize)
While other conditions can present with severe headache, they lack the characteristic "worst headache of life" presentation:
- Spontaneous intracranial hypotension: Presents with orthostatic headache (absent/mild on waking, worsens within 2 hours of upright position) 1
- Migraine: Headache builds over minutes to hours, not instantaneous peak intensity 1
- Thunderclap headache from other causes: SAH remains the most likely and dangerous cause requiring immediate exclusion 1
Common Pitfalls to Avoid
- Dismissing the complaint because the patient has a history of migraines—aneurysmal SAH can occur in anyone 1, 5
- Accepting a negative CT without lumbar puncture when clinical suspicion is high 1, 2
- Delaying transfer to a neurovascular center—early neurosurgical or endovascular intervention is critical to prevent rebleeding 2, 5
- Missing sentinel headaches in the preceding weeks, which represent a critical opportunity for intervention before catastrophic rupture 1, 5