USMLE Prep - Medical Reference Library

Acute Ischemic Stroke - Noncontrast CT, CTA, and CT Perfusion

System: Radiology • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Rapid noncontrast CT excludes hemorrhage; CTA identifies large vessel occlusion; CT perfusion or MRI can select candidates for extended window thrombectomy.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

Acute focal deficits with precise time of onset demand immediate differentiation of ischemia from hemorrhage. Obtain non‑contrast CT to exclude bleed and assess for early ischemic changes; check glucose and BP, and screen for thrombolysis contraindications. Use vessel/perfusion imaging when available to define large‑vessel occlusion and salvageable penumbra. Risk‑benefit assessment should consider pre‑morbid function, anticoagulant exposure, and imaging core size to guide IV thrombolysis and thrombectomy decisions.


Treatment Strategy & Disposition

For eligible patients within the window, administer IV thrombolysis after BP control (≤185/110 mmHg) and proceed to mechanical thrombectomy for LVO per imaging criteria. Maintain normoxia, euglycemia, and normothermia; avoid routine hypotonic fluids. Initiate antiplatelet therapy after post‑thrombolysis imaging excludes hemorrhagic transformation; manage atrial fibrillation with anticoagulation on a delayed schedule based on infarct size. Early dysphagia screening, DVT prophylaxis, and mobilization reduce complications. Admit to a stroke unit/ICU depending on severity and need for neuro‑monitoring and BP titration.


Epidemiology / Risk Factors

  • Risk factors vary by condition and patient profile

Investigations

TestRole / RationaleTypical FindingsNotes
CBCBaseline hematologyAbnormal counts
BMPElectrolytes/renalDerangements

Typical Workflow

StepTarget time
CT start to reportMinutes
CTA completionImmediate after CT
Perfusion when indicatedProtocol driven

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Alteplase (IV)Plasminogen activationMinutesWithin eligibility windowICH risk; strict contraindications
Aspirin (after lysis window)COX-1 inhibitionHoursSecondary preventionBleeding
Tenecteplase (IV bolus)Plasminogen activationMinutesAlternative to alteplase in select settingsICH risk
Dual antiplatelet (short course)ASA + clopidogrelHoursMinor stroke/TIA early periodBleeding
BP control individualizedSee HTN agentsMinutesPre/post-reperfusionHypotension risk

Prognosis / Complications

  • Prognosis depends on severity, comorbidities, and timeliness of care

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Use low motion protocols and contrast optimization. Follow stroke center pathways.


References

  1. AHA ASA acute ischemic stroke imaging guidance — Link
  2. ACR Appropriateness Criteria - Cerebrovascular Disease — Link