Perfusion CT is the Most Helpful Diagnostic Study for This Patient
For this patient presenting with wake-up stroke (unknown time of onset, last seen normal 8 hours ago), perfusion computed tomography (CTP) is the most helpful diagnostic study to determine mechanical thrombectomy eligibility because he falls into the extended time window (6-24 hours from last known well) where advanced imaging demonstrating salvageable tissue is mandatory. 1
Time-Based Imaging Algorithm
Extended Window (6-24 Hours) - This Patient's Scenario
- CTP or DW-MRI with perfusion is required to determine thrombectomy eligibility when patients present beyond 6 hours from last known well 1
- The imaging must demonstrate a sizable mismatch between the ischemic core and hypoperfusion area to identify salvageable brain tissue 1
- Strict adherence to DAWN or DEFUSE-3 criteria is mandatory for patient selection beyond 6 hours, both of which used perfusion imaging as their eligibility criteria 1
Early Window (0-6 Hours) - Not Applicable Here
- In contrast, if this patient had been within 6 hours of symptom onset, CTP would not be necessary for thrombectomy decision-making 1
- Noncontrast CT plus CTA would be sufficient if ASPECTS ≥6, NIHSS ≥6, and large vessel occlusion is confirmed 1
Essential Initial Imaging Still Required
- Noncontrast CT head must be performed immediately to exclude hemorrhage and assess ASPECTS score 1
- CT angiography should be obtained simultaneously to identify large vessel occlusion 1
- However, these baseline studies alone are insufficient for thrombectomy decision-making in the extended window 1
Laboratory Studies - Secondary Priority
- aPTT and INR should be obtained but must not delay reperfusion therapy 1
- Only blood glucose measurement must precede IV alteplase 1
- These lab values do not determine thrombectomy eligibility in the same way perfusion imaging does 1
Critical Pitfall to Avoid
Recanalization can cause CTP software to erroneously underestimate core infarct volume - the entire composite of imaging (including noncontrast CT and CTA) must be examined together when making decisions, not relying solely on automated perfusion software analysis 2. If there is gross discrepancy between visible infarct on noncontrast CT and the perfusion-calculated core volume, suspect spontaneous recanalization 2.
Supporting Evidence for Extended Window Selection
Research demonstrates that while patients selected solely on noncontrast CT and CTA in the extended window can achieve decent functional outcomes, the landmark trials establishing benefit beyond 6 hours (DAWN, DEFUSE-3) specifically used perfusion imaging for patient selection 1, 3. Without perfusion imaging in the extended window, you cannot reliably identify the patients most likely to benefit from thrombectomy 1.