A 58-year-old woman with atrial fibrillation presents 6 hours after onset of acute right-sided hemiparesis and aphasia. Non-contrast CT head excludes hemorrhage. MRI brain with DWI confirms acute left middle cerebral artery (MCA) territory infarction. Which additional imaging study is most appropriate to identify large vessel occlusion and guide mechanical thrombectomy candidacy?

Explanation

## Investigation of Choice for Large Vessel Occlusion Detection **Key Point:** CT angiography (CTA) is the fastest, most widely available, and most sensitive imaging modality for detecting large vessel occlusion (LVO) in acute ischemic stroke and directly guides mechanical thrombectomy candidacy. ### Why CTA is the Gold Standard for LVO Detection ```mermaid flowchart TD A["Acute ischemic stroke confirmed on DWI-MRI"]:::outcome --> B{"Large vessel occlusion?"}:::decision B -->|"Suspected LVO"| C["CTA head & neck"]:::action C --> D{"LVO present?"}:::decision D -->|"Yes: ICA, MCA-M1, basilar"| E["Mechanical thrombectomy candidate"]:::action D -->|"No: distal occlusion or no LVO"| F["Medical management ± thrombolysis"]:::action B -->|"Clinical suspicion low"| G["MRA or Doppler if CTA unavailable"]:::action ``` ### Comparison of LVO Detection Modalities | Modality | Sensitivity for LVO | Specificity | Speed | Availability | Radiation | Best Use | |----------|-------------------|-------------|-------|--------------|-----------|----------| | **CTA** | **95–100%** | **95–99%** | **< 1 min** | **Excellent** | **Yes** | **First-line for LVO** | | MRA (TOF) | 85–95% | 90–95% | 5–10 min | Good | No | Alternative if CTA contraindicated | | Transcranial Doppler | 85–95% | 80–90% | 10–15 min | Operator-dependent | No | Bedside screening; poor acoustic windows in 10–20% | | CT perfusion | Not designed for LVO | Detects hypoperfusion | 5 min | Excellent | Yes | Identifies penumbra; complements CTA | | Conventional angiography | 100% | 100% | 30–60 min | Limited | Yes | **Therapeutic**, not diagnostic | **High-Yield:** CTA can be performed **immediately after non-contrast CT** (same scanner, same room) and provides: 1. **Vessel patency status** (ICA, MCA-M1, MCA-M2, basilar artery) 2. **Collateral circulation** assessment 3. **Thrombus location and extent** 4. **Aortic arch anatomy** for thrombectomy planning **Clinical Pearl:** In this patient at 6 hours post-onset with confirmed acute MCA infarction, CTA is essential because: - She is **within the mechanical thrombectomy window** (up to 24 hours if imaging shows salvageable tissue) - **LVO presence directly determines candidacy** for thrombectomy vs. medical management alone - CTA is faster and more sensitive than MRA for proximal vessel occlusion - Results are immediately actionable for interventional radiology consultation **Mnemonic:** **CTA = Can Thrombectomy Achieve (reperfusion)?** — it answers the critical question for intervention. ### Why Other Modalities Are Suboptimal - **CT perfusion:** Identifies tissue at risk (penumbra) but does NOT directly visualize vessel occlusion; used as **adjunct to CTA**, not replacement - **Transcranial Doppler:** Operator-dependent; poor acoustic windows in 10–20% of patients; cannot definitively exclude distal occlusions; used for bedside screening only - **MRA (TOF):** Slightly lower sensitivity than CTA for proximal LVO; takes longer; not first-line when CTA available - **Conventional angiography:** Invasive; reserved for **therapeutic thrombectomy**, not diagnostic confirmation