Residency · Residency · Interventional Radiology
Acute Ischemic Stroke: Mechanical Thrombectomy Overview
Overview
Mechanical thrombectomy (MT) is the standard of care for acute ischemic stroke caused by large vessel occlusion (LVO). Multiple landmark RCTs (2015) demonstrated dramatic benefit over medical therapy alone. Time window extended to 24 hours with advanced imaging selection (DAWN, DEFUSE-3 trials). IR trainees may participate in stroke call depending on institutional practice and scope of training.
Large Vessel Occlusion Identification
Target Vessels
Internal carotid artery (ICA) terminus. Middle cerebral artery (MCA) M1 and proximal M2 segments. Basilar artery. Vertebral artery (V4 segment). Anterior cerebral artery (less common indication; emerging evidence).
Clinical Assessment
NIHSS (National Institutes of Health Stroke Scale): ≥6 suggests LVO. Rapid neurologic assessment: facial droop, arm weakness, speech difficulty. Field screening tools: FAST (Face, Arms, Speech, Time), RACE, LAMS. Activation of stroke code pathway and rapid transport to thrombectomy-capable center.
Imaging
Non-contrast CT head: rule out hemorrhage (must precede any intervention). CT angiography (CTA): identifies LVO location, collateral status, and cervical vessel pathology. Single-phase or multiphase CTA. Collateral grading predicts outcome. CT perfusion (CTP): defines ischemic core (irreversibly damaged tissue) vs. penumbra (salvageable tissue). Core: CBF <30% of normal (or rCBF <30%). Penumbra: Tmax >6 seconds. Mismatch ratio: penumbra / core — large mismatch favors intervention. MRI (DWI/PWI): alternative to CTP; diffusion restriction shows ischemic core; perfusion-weighted imaging shows penumbra.
<image>CT perfusion maps showing a large ischemic penumbra (Tmax >6s, green) with a small ischemic core (CBF <30%, red) in a patient with right MCA M1 occlusion, demonstrating a favorable mismatch for thrombectomy</image>
Patient Selection
Key Thrombectomy Trials
| Trial | Year | Time Window | Key Finding |
|---|---|---|---|
| MR CLEAN | 2015 | 0-6 hr | First positive RCT for MT in LVO |
| ESCAPE | 2015 | 0-12 hr | Benefit with good collaterals |
| EXTEND-IA | 2015 | 0-6 hr | CT perfusion selection; NNT=3 |
| SWIFT PRIME | 2015 | 0-6 hr | Stent retriever benefit over IV tPA alone |
| REVASCAT | 2015 | 0-8 hr | Benefit up to 8 hours |
| DAWN | 2018 | 6-24 hr | Clinical-imaging mismatch; NNT=2.8 |
| DEFUSE-3 | 2018 | 6-16 hr | Perfusion mismatch selection |
| ATTENTION | 2022 | 0-24 hr | Basilar artery occlusion benefit |
Standard Window (0-6 Hours)
Based on trials: MR CLEAN, ESCAPE, EXTEND-IA, SWIFT PRIME, REVASCAT. Criteria: LVO (ICA terminus or MCA M1). NIHSS ≥6. ASPECTS ≥6 on NCCT (Alberta Stroke Program Early CT Score). Pre-stroke functional independence (mRS 0-1). Treatment initiated within 6 hours of symptom onset. IV tPA administered if within 4.5-hour window (MT should NOT be delayed for IV tPA).
Extended Window (6-24 Hours)
DAWN trial (6-24 hours): clinical-imaging mismatch. Age ≥80: NIHSS ≥10 and core <21 mL. Age <80: NIHSS ≥10 and core <31 mL, or NIHSS ≥20 and core <51 mL. DEFUSE-3 trial (6-16 hours): perfusion imaging mismatch. Core <70 mL. Mismatch ratio ≥1.8. Mismatch volume ≥15 mL. These trials dramatically expanded the treatment population and demonstrated overwhelming benefit (NNT ~2-3).
Basilar Artery Occlusion
ATTENTION and BAOCHE trials (2022): demonstrated benefit of thrombectomy for basilar artery occlusion within 24 hours. High morbidity and mortality without treatment (mortality ~80-90%). Thrombectomy significantly improves functional outcomes.
Thrombectomy Technique
Access
Common femoral artery (most common) or radial artery access. 8-9 Fr femoral sheath; long sheath or balloon-guide catheter (BGC) advanced to ICA or vertebral artery. Balloon-guide catheter: inflated during thrombectomy to arrest antegrade flow and reduce distal embolization.
Stent Retriever Technique
Microcatheter navigated past the thrombus over a microwire. Stent retriever (Solitaire, Trevo) deployed across the thrombus. Wait 3-5 minutes for thrombus integration into the stent struts. Inflate BGC; apply continuous aspiration through guide catheter. Withdraw stent retriever with trapped thrombus. Repeat until TICI 2b/3 flow achieved (up to 3-5 passes).
Direct Aspiration First Pass Technique (ADAPT)
Large-bore aspiration catheter (Penumbra ACE, Sofia, React) advanced directly to the face of the thrombus. Continuous aspiration applied; catheter withdrawn with thrombus. Can be faster than stent retriever for certain clot types. Combined approach (aspiration + stent retriever) also widely used.
Revascularization Grading (TICI Score)
TICI 0: no perfusion. TICI 1: penetration with minimal perfusion. TICI 2a: partial filling of <50% of the expected territory. TICI 2b: complete filling of >50% of expected territory (acceptable result). TICI 2c: near-complete reperfusion with slow flow in distal branches. TICI 3: complete reperfusion. Goal: TICI 2b or better (achieved in 80-90% of cases with modern devices).
<image>Sequential angiographic images during mechanical thrombectomy of a left MCA M1 occlusion showing pre-intervention occlusion, stent retriever deployment across the thrombus, and post-thrombectomy TICI 3 reperfusion</image>
Outcomes
Landmark Trials (2015)
Pooled analysis (HERMES): thrombectomy reduces disability across all subgroups. NNT for functional independence (mRS 0-2): ~2.6. Absolute benefit: 20-30% more patients achieving functional independence. No increase in symptomatic intracerebral hemorrhage.
Extended Window Trials
DAWN: adjusted common OR 3.8 for functional independence; NNT ~2. DEFUSE-3: RR for functional independence 2.7; NNT ~3. These trials established that tissue-based selection (imaging) is more important than time alone.
Posterior Circulation
ATTENTION trial: mRS 0-3 at 90 days: 46% thrombectomy vs. 23% medical (OR 2.8). Basilar thrombectomy is now supported by level 1 evidence.
Scope of Practice: IR vs. Neuroradiology vs. Neurosurgery
Current Landscape
Mechanical thrombectomy is performed by: Neurointerventional radiologists. Interventional neuroradiologists. Endovascular neurosurgeons. Interventional neurologists. Some IR-trained physicians with additional neurointerventional training. Specialty-specific training pathways and credentialing vary by institution and country.
IR Trainee Role
IR residency provides foundational catheter skills applicable to stroke intervention. Additional fellowship training in neurointerventional procedures required for independent stroke call. Some programs offer dual-track or combined IR/neurointerventional training. IR trainees on stroke call teams gain exposure to emergent neurovascular decision-making. Understanding of stroke imaging, patient selection, and acute management is essential regardless of whether the IR trainee will independently perform thrombectomy.
Complications
Procedure-Related
Vessel perforation or dissection (1-5%). Distal embolization to new territory (3-9%). Subarachnoid hemorrhage (from wire perforation). Access site complications (hematoma, pseudoaneurysm). Vasospasm.
Disease-Related
Symptomatic intracerebral hemorrhage (5-8%). Reperfusion injury. Cerebral edema (malignant MCA infarction). Hemorrhagic transformation.
Clinical Pearls
Time is brain — every 15 minutes of delay in reperfusion results in measurable loss of disability-free life; minimize door-to-puncture time. IV tPA should be given when indicated but NEVER delay thrombectomy to observe the effect of IV tPA. Balloon-guide catheter use is associated with higher first-pass reperfusion rates and lower distal embolization — it should be used whenever feasible. ASPECTS scoring on NCCT is essential for patient selection in the 0-6 hour window; scores <6 indicate large established infarction with diminishing returns from thrombectomy. CT perfusion mismatch imaging has democratized extended-window stroke treatment — learn to interpret CTP maps (core vs. penumbra vs. mismatch). First-pass TICI 2c/3 reperfusion is the strongest predictor of good clinical outcome — optimize technique for first-pass success. Posterior circulation strokes have devastating outcomes without treatment but excellent response to thrombectomy — maintain a low threshold for basilar artery thrombectomy evaluation. IR trainees should understand stroke pathophysiology, imaging selection, and acute management even if not performing thrombectomy — these patients are encountered in IR practice.
<image>Non-contrast CT with ASPECTS scoring overlay showing early ischemic changes in the right MCA territory with identification of affected ASPECTS regions</image>
References
- Goyal M, et al. Endovascular Thrombectomy After Large-Vessel Ischaemic Stroke: A Meta-Analysis of Individual Patient Data (HERMES). Lancet. 2016;387(10029):1723-1731.
- Nogueira RG, et al. Thrombectomy 6 to 24 Hours After Stroke with a Mismatch Between Deficit and Infarct (DAWN Trial). N Engl J Med. 2018;378(1):11-21.
- Albers GW, et al. Thrombectomy for Stroke at 6 to 16 Hours with Selection by Perfusion Imaging (DEFUSE 3). N Engl J Med. 2018;378(8):708-718.
- Tao C, et al. Thrombectomy for Acute Basilar Artery Occlusion (ATTENTION Trial). N Engl J Med. 2022;387(15):1361-1372.
- Powers WJ, et al. AHA/ASA Guidelines for the Early Management of Patients with Acute Ischemic Stroke. Stroke. 2019;50(12):e344-e418.
- Defined JR, et al. ADAPT Technique for Stroke Thrombectomy. J Neurointerv Surg. 2014;6(7):489-495.
