What is the differential diagnosis and management of thunderclap headaches?

Differential Diagnosis of Thunderclap Headache

Life-Threatening Causes (Require Immediate Exclusion)

Subarachnoid hemorrhage (SAH) is the primary concern in any thunderclap headache presentation and must be excluded first, as it accounts for 10-25% of cases and carries 27-44% mortality. 1, 2, 3

Vascular Emergencies

• Aneurysmal subarachnoid hemorrhage: Most critical diagnosis, described by 80% of alert patients as "worst headache of my life" reaching maximal intensity within seconds to one minute 1, 2
• Reversible cerebral vasoconstriction syndrome (RCVS): Increasingly recognized as an important cause of thunderclap headache, now diagnosed more frequently with advances in neuroimaging 4, 5
• Cervical artery dissection: Presents with thunderclap headache in up to 20% of cases, though gradual onset is more typical; associated with Horner syndrome when present 1, 6
• Cerebral venous sinus thrombosis: Can present with thunderclap headache mimicking SAH, particularly when involving superior sagittal or lateral sinuses 1, 4
• Intracerebral hemorrhage: Associated with aneurysms or vascular malformations (AVMs, cavernomas) 1, 4
• Acute cerebral infarction: Less common presentation but documented cause 4

Non-Vascular Life-Threatening Causes

• Spontaneous intracranial hypotension (SIH): Thunderclap headache followed by orthostatic headache is a recognized presentation pattern 1, 4, 5
• Pituitary apoplexy: Acute hemorrhage or infarction of pituitary gland 4
• Intracranial infection: Meningitis or encephalitis with acute presentation, particularly when associated with fever and altered mental status 1

Primary (Benign) Headache Disorders

After excluding secondary causes, primary thunderclap headache represents a distinct clinical entity lasting 1 hour to 10 days, though this may represent missed diagnoses of underlying causes. 7, 5

• Primary thunderclap headache: Diagnosis of exclusion after comprehensive workup 7, 5
• Migraine with thunderclap onset: Uncommon presentation of migraine 1, 7
• Primary cough headache: Triggered by Valsalva maneuvers 7
• Primary exertional headache: Onset during physical activity 7
• Primary headache associated with sexual activity: Occurs at orgasm or during sexual activity 7

Diagnostic Algorithm

Immediate Evaluation (Within 6 Hours)

For patients presenting within 6 hours of headache onset without new neurological deficits, obtain noncontrast head CT on high-quality scanner interpreted by board-certified neuroradiologist (98.7% sensitivity, misses <1.5 in 1000 SAHs). 1, 2, 8

• Apply Ottawa SAH Rule criteria: Age ≥40 years, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, thunderclap headache, or limited neck flexion on examination 1, 2
• If any criterion met, proceed with CT imaging 1
• CT sensitivity for SAH is 98% with specificity 99% when performed acutely 1

Delayed Presentation (>6 Hours) or Negative Initial CT

For patients presenting >6 hours from symptom onset or with high clinical suspicion despite negative CT, perform lumbar puncture for xanthochromia evaluation using spectrophotometric analysis (100% sensitivity, 95.2% specificity). 1, 2, 8

• LP should be performed >6-12 hours after symptom onset for optimal xanthochromia detection 1, 8
• CT sensitivity decreases significantly after 6 hours, making LP mandatory in this timeframe 8
• Xanthochromia (yellow CSF discoloration from bilirubin) is the key diagnostic finding, not just bloodstained CSF 8

Further Vascular Imaging

If CT and LP are negative, obtain brain MRI with susceptibility-weighted imaging (SWI) and vascular imaging (CTA or MRA) to evaluate for RCVS, arterial dissection, cerebral venous thrombosis, and other vascular pathology. 1, 4, 5

• CTA has >95% sensitivity for aneurysms ≥3mm and is faster and less invasive than conventional angiography 8
• MRI with FLAIR and SWI sequences improves detection of SAH (50-94% sensitivity) and other pathology, though less sensitive than acute CT 1
• Cerebral angiography remains gold standard with >98% sensitivity and specificity for detecting aneurysms 8

Critical Pitfalls to Avoid

• Never rely on CT alone after 6 hours: CT sensitivity drops significantly with time; LP is mandatory when clinical suspicion remains high 1, 8
• Do not skip LP based on negative CT in high-risk presentations: Failure to identify SAH leads to nearly 4-fold higher likelihood of death or disability 2
• Recognize atypical presentations: Primary neck pain, syncope, seizure, or new focal neurological deficit may not fit classic thunderclap pattern but still require full workup 1
• Avoid misinterpreting FLAIR sequences: Artifactual sulcal hyperintensity can occur in children receiving propofol and supplemental oxygen, mimicking SAH 1
• Consider timing for xanthochromia: Testing before 12 hours may reduce sensitivity, though earlier testing may still be clinically appropriate 8

Special Populations

• Patients with first-degree relatives with aneurysms or vascular abnormalities: Neuroimaging indicated even with atypical presentations, as these conditions are familial 1
• Autosomal dominant polycystic kidney disease (ADPKD): Increased risk for intracranial aneurysms; educate patients to recognize thunderclap headache as requiring immediate medical attention 2
• Children: Thunderclap headaches are rare; evidence-based approach extrapolated from adult populations 1

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