Anterior-Circulation Mechanical Thrombectomy

01

Current guideline context {#current-guideline-context}

The current normative source is the 2026 American Heart Association/American Stroke Association acute ischemic stroke guideline. For patients with internal carotid artery or M1 occlusion, NIHSS score at least 6, prestroke modified Rankin Scale (mRS) score 0 to 1, and no major conflicting boundary, it gives Class 1, Level A recommendations for:

• thrombectomy within 6 hours when ASPECTS is 3 to 10; and
• thrombectomy from 6 to 24 hours when ASPECTS is at least 6.

The guideline also incorporates newer large-core evidence. It recommends thrombectomy from 6 to 24 hours for selected patients younger than 80 years with ICA or M1 occlusion, NIHSS at least 6, prestroke mRS 0 to 1, ASPECTS 3 to 5, and no significant mass effect. For similarly selected patients with ASPECTS 0 to 2 within 6 hours, thrombectomy is considered reasonable rather than supported by the same breadth of evidence. [1]

These statements describe a guideline framework, not a stand-alone bedside checklist. Anatomy, time anchor, baseline function, clinical severity, predicted core, mass effect, technical feasibility, and goals of care remain connected.

02

The early-window evidence foundation {#early-window}

Five landmark trials published in 2015—MR CLEAN, ESCAPE, REVASCAT, SWIFT PRIME, and EXTEND-IA—used different imaging and workflow strategies but consistently favored thrombectomy for proximal anterior-circulation occlusion. The HERMES collaboration pooled individual patient data from those trials and confirmed a favorable shift across the 90-day mRS, with a number needed to treat of approximately 2.6 for one patient to improve by at least one disability level. [2]

The practical change was not simply “a device works.” The trials linked three ideas:

1. demonstrate an eligible proximal occlusion;
2. use modern thrombectomy techniques at capable centers; and
3. avoid preventable delay.

The trials were not interchangeable. They differed in collateral assessment, perfusion selection, enrollment window, workflow targets, device strategy, and background intravenous thrombolysis. HERMES supports a common treatment effect across the pooled population, but it does not manufacture one imaging protocol from five different designs. The current guideline also emphasizes that benefit decreases with treatment delay. [1] [2]

03

Late-window treatment is selection-dependent {#late-window}

Late-window thrombectomy became established through two complementary randomized trials.

DAWN

DAWN randomized 206 patients with intracranial ICA or proximal M1 occlusion 6 to 24 hours after last known well. Enrollment required an age-adjusted mismatch between a severe clinical deficit and a relatively small automated imaging-defined core. Functional independence at 90 days was 49% with thrombectomy versus 13% with standard care; symptomatic intracranial hemorrhage and mortality did not differ significantly. The trial stopped early. [3]

DAWN established a strong result in a narrow clinical-core mismatch population. Its age, NIHSS, anatomy, core-volume, baseline-function, and software boundaries should not be rewritten as a general statement that any proximal occlusion remains treatable through 24 hours.

DEFUSE 3

DEFUSE 3 randomized 182 patients with ICA or proximal M1 occlusion 6 to 16 hours after last known well. RAPID processing had to show a core below 70 mL, a perfusion-to-core ratio at least 1.8, and at least 15 mL of potentially reversible ischemia. Thrombectomy improved the 90-day disability distribution and functional independence, 45% versus 17%; symptomatic intracranial hemorrhage did not differ significantly. [4]

DEFUSE 3 extended benefit to a perfusion-core mismatch population that was not identical to DAWN. It also stopped early and was conducted at experienced centers using automated processing.

What should not be blended

DAWN used age- and NIHSS-dependent clinical-core mismatch through 24 hours. DEFUSE 3 used core volume, mismatch ratio, and minimum penumbral volume through 16 hours. Both support tissue-informed late-window selection, but combining pieces of each into a hybrid criterion creates a protocol that neither trial tested.

04

Large-core evidence expanded eligibility {#large-core}

The original thrombectomy trials largely favored patients with smaller predicted cores. RESCUE-Japan LIMIT, ANGEL-ASPECT, SELECT2, TENSION, TESLA, and LASTE then tested populations with more extensive established injury using trial-specific combinations of ASPECTS, quantitative core estimates, imaging modality, and time window. [1] [5] [6] [7] [8]

The 2026 guideline reports that five of six recent randomized trials showed functional benefit for anterior-circulation occlusion with ASPECTS 3 to 5. Across those trials, thrombectomy more than doubled functional independence compared with medical therapy, although independence remained uncommon: approximately 19.5% versus 7.5%. The estimated number needed to treat to prevent one additional instance of functional dependence was 8. [1]

This is a meaningful expansion, not a return to indiscriminate treatment. The trials differed in:

• ASPECTS range and quantitative core thresholds;
• CT, MRI, and perfusion-based selection;
• early versus extended treatment windows;
• geography, workflow, and background care;
• age and prestroke disability exclusions; and
• primary disability and safety outcomes.

ASPECTS 0 to 2 remains a narrower evidence lane. LASTE supplied much of the randomized evidence, enrolled within 6.5 hours, excluded patients 80 years or older, and used MRI diffusion imaging for many very-low-ASPECTS patients. Other positive trials included relatively small off-protocol subgroups. [1] [8]

05

Evidence-to-practice conclusions {#evidence-to-practice}

• Early-window proximal ICA/M1 occlusion: thrombectomy is established, time-sensitive care for eligible patients.
• Six to 24 hours: treatment is also established for selected patients, but late-window evidence is inseparable from the clinical and imaging context used to identify likely benefit.
• ASPECTS 3 to 5: recent randomized evidence supports treatment expansion across early and late windows in appropriately selected patients.
• ASPECTS 0 to 2: benefit is plausible and guideline-supported as reasonable in a narrower early-window population, but confidence and generalizability are lower.
• Across all windows: a favorable group-level treatment effect does not guarantee independence for an individual patient, particularly with a large predicted core.

06

Where the evidence is less certain {#evidence-gaps}

Important underrepresented or incompletely resolved groups include mild deficits with proximal occlusion, major prestroke disability, marked mass effect, severe medical comorbidity, suspected intracranial atherosclerotic disease, very advanced age in the very-large-core population, and workflows that differ substantially from the trial settings. Distal and medium-vessel occlusions require a separate evidence review and are outside this article.

Practical CTA, CTP, and MRI interpretation is also outside this article. Imaging labels such as “core,” “mismatch,” or “favorable profile” should not substitute for the exact definitions, software, modality, and time window used in the supporting trial.

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07

Education-only boundary {#education-only}

This summary explains evidence and current guideline context. It does not replace local stroke-system procedures, multidisciplinary assessment, device instructions, transfer agreements, or individualized treatment decisions.

08

References {#references}

1. Prabhakaran S, et al. 2026 Guideline for the Early Management of Patients With Acute Ischemic Stroke: A Guideline From the American Heart Association/American Stroke Association. Stroke. 2026;57:e00-e00. doi:10.1161/STR.0000000000000513
2. Goyal M, Menon BK, van Zwam WH, et al; HERMES collaborators. Endovascular thrombectomy after large-vessel ischaemic stroke: a meta-analysis of individual patient data from five randomised trials. Lancet. 2016;387:1723-1731. doi:10.1016/S0140-6736(16)00163-X00163-X)
3. Nogueira RG, Jadhav AP, Haussen DC, et al; DAWN Trial Investigators. Thrombectomy 6 to 24 hours after stroke with a mismatch between deficit and infarct. N Engl J Med. 2018;378:11-21. doi:10.1056/NEJMoa1706442
4. Albers GW, Marks MP, Kemp S, et al; DEFUSE 3 Investigators. Thrombectomy for stroke at 6 to 16 hours with selection by perfusion imaging. N Engl J Med. 2018;378:708-718. doi:10.1056/NEJMoa1713973
5. Yoshimura S, Sakai N, Yamagami H, et al. Endovascular therapy for acute stroke with a large ischemic region. N Engl J Med. 2022;386:1303-1313. doi:10.1056/NEJMoa2118191
6. Sarraj A, Hassan AE, Abraham MG, et al; SELECT2 Investigators. Trial of endovascular thrombectomy for large ischemic strokes. N Engl J Med. 2023;388:1259-1271. doi:10.1056/NEJMoa2214403
7. Bendszus M, Fiehler J, Subtil F, et al; TENSION Investigators. Endovascular thrombectomy for acute ischaemic stroke with established large infarct: multicentre, open-label, randomised trial. Lancet. 2023;402:1753-1763. doi:10.1016/S0140-6736(23)02032-902032-9)
8. Costalat V, Jovin TG, Albucher JF, et al; LASTE Trial Investigators. Trial of thrombectomy for stroke with a large infarct of unrestricted size. N Engl J Med. 2024;390:1677-1689. doi:10.1056/NEJMoa2314063

09

References

1. Prabhakaran S, et al. 2026 Guideline for the Early Management of Patients With Acute Ischemic Stroke: A Guideline From the American Heart Association/American Stroke Association. Stroke. 2026;57:e00-e00.
2. Goyal M, Menon BK, van Zwam WH, et al; HERMES collaborators. Endovascular thrombectomy after large-vessel ischaemic stroke: a meta-analysis of individual patient data from five randomised trials. Lancet. 2016;387:1723-1731.
3. Nogueira RG, Jadhav AP, Haussen DC, et al; DAWN Trial Investigators. Thrombectomy 6 to 24 hours after stroke with a mismatch between deficit and infarct. N Engl J Med. 2018;378:11-21.
4. Albers GW, Marks MP, Kemp S, et al; DEFUSE 3 Investigators. Thrombectomy for stroke at 6 to 16 hours with selection by perfusion imaging. N Engl J Med. 2018;378:708-718.
5. Yoshimura S, Sakai N, Yamagami H, et al. Endovascular therapy for acute stroke with a large ischemic region. N Engl J Med. 2022;386:1303-1313.
6. Sarraj A, Hassan AE, Abraham MG, et al; SELECT2 Investigators. Trial of endovascular thrombectomy for large ischemic strokes. N Engl J Med. 2023;388:1259-1271.
7. Bendszus M, Fiehler J, Subtil F, et al; TENSION Investigators. Endovascular thrombectomy for acute ischaemic stroke with established large infarct: multicentre, open-label, randomised trial. Lancet. 2023;402:1753-1763.
8. Costalat V, Jovin TG, Albucher JF, et al; LASTE Trial Investigators. Trial of thrombectomy for stroke with a large infarct of unrestricted size. N Engl J Med. 2024;390:1677-1689.