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Thunderclap Headache Evaluation

Thunderclap Headache Evaluation: Thunderclap Headache Presentation → Assess Clinical Features → Ottawa SAH Rule → Non-Contrast CT Head → CT Result?.

Interactive Decision Tree

Mini Map

Algorithm Steps

  1. ▶
    Start

    Thunderclap Headache Presentation

    Severe headache reaching maximum intensity within seconds to 1 minute

    1. ●
      Action

      Assess Clinical Features

      High-risk features for SAH

      • Sudden onset (seconds to minutes)
      • 'Worst headache of life'
      • Neck stiffness
      • Loss of consciousness
      • Focal neurological deficit
      • Sentinel headache history
      1. ●
        Action

        Ottawa SAH Rule

        Clinical decision rule (if applicable)

        • Age ≥40
        • Witnessed LOC
        • Neck pain/stiffness
        • Onset during exertion
        • Thunderclap onset
        • Limited neck flexion
        • ANY = investigate
        1. ●
          Action

          Non-Contrast CT Head

          First-line imaging, ASAP

          • Sensitivity ~98% if within 6 hours
          • Sensitivity drops to ~90% at 24h
          • ~50% at 1 week
          • Look for subarachnoid blood
          1. ◆
            Decision

            CT Result?

            Blood present?

            1. ⚠
              Warning

              CT Positive: SAH Confirmed

              Blood visible on CT

              • Consult neurosurgery immediately
              • CTA or DSA to find source
              • ICU admission
              • Blood pressure management
              • Nimodipine for vasospasm prevention
              1. ●
                Action

                CTA or DSA

                Find aneurysm source

                • CTA: non-invasive, widely available
                • DSA: gold standard, interventional
                • 10-15% aneurysmal SAH: negative initial angiogram
                • May need repeat imaging
                1. ●
                  Action

                  Aneurysm Treatment

                  Secure the aneurysm

                  • Coiling (endovascular) vs Clipping (surgical)
                  • Decision by neurosurgery/neurointerventional
                  • Goal: prevent rebleeding
                  • Treat within 24-72 hours
                  1. ✓
                    Outcome

                    SAH Management

                    ICU care, prevent complications

                    • Nimodipine for vasospasm
                    • Blood pressure control
                    • Seizure prophylaxis (controversial)
                    • Monitor for hydrocephalus
            2. ◆
              Decision

              CT Negative

              Proceed to LP or CTA?

              • Controversy: LP vs CTA-first approach
              • Traditional: LP after negative CT
              • Modern: Some advocate CTA if <6h
              • Context-dependent decision
              1. ●
                Action

                If CT within 6h of Onset

                High sensitivity window

                • CT sensitivity ~98-100% at <6h
                • Some centers: CTA without LP
                • Low-risk patients may be discharged
                • Shared decision-making
                1. ✓
                  Outcome

                  Discharge if SAH Ruled Out

                  Follow-up as needed

                  • Primary care or neurology follow-up
                  • Return precautions
                  • Consider migraine workup if recurrent
              2. ●
                Action

                Lumbar Puncture

                If CT negative, >6h, or any doubt

                • Ideally >6-12h after onset
                • Opening pressure, cell count, protein
                • CSF for xanthochromia
                • Send tube 1 and 4 for RBC comparison
                1. ◆
                  Decision

                  LP Results

                  Interpret CSF findings

                  • Xanthochromia: yellow CSF = SAH
                  • RBCs not clearing: may be SAH
                  • RBCs clearing (traumatic tap): less concern
                  • Spectrophotometry if available
                  1. ⚠
                    Warning

                    LP Positive for SAH

                    Xanthochromia or persistent RBCs

                    • Proceed to CTA/DSA
                    • Neurosurgery consult
                    • Treat as SAH until proven otherwise
                  2. ●
                    Action

                    LP Negative

                    No xanthochromia, clearing RBCs

                    • SAH effectively ruled out
                    • Consider other causes
                    • RCVS, cervical dissection, CVT
                    • May still need CTA if high suspicion
                    1. ●
                      Action

                      Consider Other Causes

                      If SAH ruled out

                      • RCVS (reversible cerebral vasoconstriction)
                      • Cervical artery dissection
                      • Cerebral venous thrombosis
                      • Pituitary apoplexy
                      • Primary thunderclap headache

Guideline Source

AHA/ASA SAH Guidelines + ACEP Clinical Policy on Headache

DOI: 10.1161/STR.0000000000000407View Guideline

Clinical Safety Information

Clinical Decision Support — Not a Substitute for Clinical Judgment

Individual patient factors may require deviation from these recommendations.

Known Limitations

  • CT sensitivity decreases with time from onset
  • LP interpretation requires expertise
  • CTA may miss small aneurysms
  • Other causes of thunderclap exist

Applicable Regions

USEUglobal

EU: Similar approach, some centers use CTA first

US: AHA/ASA and ACEP guidelines

Version 1Next review: 2027-01-01

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Frequently Asked Questions

What is the Thunderclap Headache Evaluation?

The Thunderclap Headache Evaluation is a diagnostic clinical algorithm for Neurology. It provides a structured decision tree to guide clinical decision-making, based on AHA/ASA SAH Guidelines + ACEP Clinical Policy on Headache.

What guideline is the Thunderclap Headache Evaluation based on?

This algorithm is based on AHA/ASA SAH Guidelines + ACEP Clinical Policy on Headache (DOI: 10.1161/STR.0000000000000407).

What are the limitations of the Thunderclap Headache Evaluation?

Known limitations include: CT sensitivity decreases with time from onset; LP interpretation requires expertise; CTA may miss small aneurysms; Other causes of thunderclap exist. Individual patient factors may require deviation from these recommendations.

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