A 72-year-old woman with atrial fibrillation presents with acute aphasia and right-sided weakness. Non-contrast CT head excludes hemorrhage. Bedside NIHSS is 15. Which investigation is most appropriate to identify the culprit vessel and determine candidacy for mechanical thrombectomy?

Explanation

## Investigation for Large Vessel Occlusion Detection in Acute Stroke **Key Point:** CTA of the head and neck is the rapid, non-invasive imaging modality of choice to identify large vessel occlusion (LVO) and determine mechanical thrombectomy candidacy in acute ischemic stroke. ### Clinical Context This patient has: - Acute stroke symptoms (aphasia + right-sided weakness → left hemisphere) - High NIHSS (15) suggesting severe stroke - Atrial fibrillation (cardioembolic source likely) - Time window for intervention (hyperacute phase) **High-Yield:** Patients with LVO (internal carotid artery, M1/M2 middle cerebral artery) benefit from **mechanical thrombectomy** if presented within 24 hours (extended window) and meet imaging criteria. CTA is the fastest way to identify LVO. ### Why CTA is the Investigation of Choice | Feature | CTA | CTP | Conventional Angiography | Duplex US | |---|---|---|---|---| | **Detects LVO** | ✓ Excellent | ✗ No | ✓ Yes, but invasive | ✗ Limited to carotid | | **Speed** | ~1 min | ~5 min | 20–30 min | ~10 min | | **Invasiveness** | Non-invasive | Non-invasive | Invasive | Non-invasive | | **Radiation** | Yes | Yes | Yes | No | | **Clinical role** | **Diagnostic** | Prognostic (ischemic core vs penumbra) | Therapeutic (rarely diagnostic now) | Screening only | **Clinical Pearl:** CTA is performed **immediately after non-contrast CT** in acute stroke protocols. It takes <2 minutes and provides: - Vessel patency (identifies occlusion site) - Collateral circulation assessment - Thrombus location and extent - Eligibility for thrombectomy ### Mnemonic **CTA = CT Angiography = Culprit Thrombus Anatomy** ### Role of Other Investigations - **CT Perfusion (CTP):** Assesses tissue viability (ischemic core vs penumbra) to guide extended-window thrombectomy decisions, but does NOT identify the vessel occlusion itself. - **Conventional Angiography:** Gold standard for diagnosis but invasive and time-consuming; reserved for therapeutic intervention (thrombectomy) once CTA has identified LVO. - **Carotid Duplex:** Useful for chronic carotid stenosis screening; cannot assess intracranial vessels or acute occlusion adequately. [cite:Harrison 21e Ch 370]