A 62-year-old man presents to the emergency department with acute onset left-sided weakness and speech difficulty of 2 hours duration. Non-contrast CT head is normal. Which investigation is most appropriate to confirm acute ischemic stroke and guide thrombolytic therapy?

Explanation

## Investigation of Choice for Acute Ischemic Stroke Confirmation **Key Point:** DWI-MRI is the gold standard for detecting acute cerebral ischemia within minutes of symptom onset, when conventional CT and standard MRI sequences remain normal. ### Why DWI-MRI is Superior Diffusion-weighted imaging detects restricted water movement in ischemic tissue due to cytotoxic edema. This occurs within **minutes** of arterial occlusion, making DWI the most sensitive and specific modality for acute stroke diagnosis. **High-Yield:** DWI shows hyperintensity (bright signal) in acute ischemia, corresponding to restricted diffusion on the apparent diffusion coefficient (ADC) map. This allows: - Differentiation of acute from chronic/old infarcts - Detection of very early infarcts (< 6 hours) when CT is still normal - Identification of multiple infarcts in different vascular territories - Guidance for thrombolytic therapy eligibility ### Comparison of Acute Stroke Imaging Modalities | Modality | Timing | Sensitivity (Acute) | Clinical Use | |----------|--------|---------------------|---------------| | **Non-contrast CT** | Immediate | ~10% (detects only hemorrhage/hypodensity) | Rules out hemorrhage | | **DWI-MRI** | Minutes | >90% | Confirms acute ischemia, guides therapy | | **CT Perfusion** | Minutes | ~80% | Identifies ischemic penumbra, tissue viability | | **MRA** | Minutes | Variable | Assesses large vessel patency | | **Conventional angiography** | 30–60 min | High | Therapeutic (thrombectomy), not diagnostic | **Clinical Pearl:** In a patient with normal CT but high clinical suspicion for acute stroke, DWI-MRI should be obtained urgently. If MRI is contraindicated or unavailable, CT perfusion is the next best alternative to assess tissue viability and guide intervention. ### Timing and Thrombolytic Eligibility DWI-MRI helps determine: 1. **Acute vs. chronic infarct** — acute infarcts show DWI hyperintensity + ADC hypointensity (restricted diffusion) 2. **Tissue viability** — presence of ischemic penumbra (tissue at risk) on perfusion-weighted imaging (PWI) 3. **Thrombolytic window** — DWI/PWI mismatch suggests salvageable tissue, supporting thrombolysis even beyond 4.5 hours in select cases **Mnemonic:** **DWI = Diffusion Weighted Imaging = Detects early Ischemia** — the most sensitive modality for acute stroke diagnosis. [cite:Harrison 21e Ch 370]