Posterior-Circulation Mechanical Thrombectomy

01

Why posterior circulation is different {#posterior-differences}

The vertebral arteries converge into the basilar artery, which supplies the brainstem and contributes to cerebellar, thalamic, and occipital circulation through its branches and terminal posterior cerebral arteries. Collateral support can arrive through posterior communicating arteries and cerebellar connections, but its adequacy and clinical expression vary.

This anatomy changes the bedside problem. A proximal anterior-circulation occlusion commonly produces a cortical hemispheric syndrome. Basilar occlusion can instead combine cranial-nerve findings, dysarthria or dysphagia, gaze or ocular-motor abnormalities, ataxia, bilateral weakness or sensory change, fluctuating consciousness, or coma. Some highly consequential posterior deficits are incompletely represented by the NIHSS, while extensive brainstem injury may be devastating even when a hemispheric “core-volume” model does not apply. [1] [2]

Selection and outcome measurement therefore differ too:

• Imaging injury score: posterior trials used PC-ASPECTS and, in BAOCHE, an additional pons-midbrain injury limit rather than simply importing anterior ASPECTS or perfusion-core thresholds.
• Time anchor: prodromal or fluctuating symptoms may complicate the estimated onset of the occlusion; the trials used their own onset or last-known-well definitions.
• Clinical severity: NIHSS helps define trial populations but can underrepresent selected brainstem, gait, ocular-motor, or bulbar deficits.
• Outcome: the modified Rankin Scale captures global disability and mortality, but it does not separately describe vision, swallowing, cranial-nerve, gait, or consciousness burdens.

These differences help explain why posterior thrombectomy evidence matured later: fewer eligible cases, heterogeneous presentations and natural histories, difficulty maintaining equipoise, and treatment outside randomized pathways made adequately powered enrollment harder.

02

Current 2026 guideline context {#current-guideline-context}

The normative source is the 2026 American Heart Association/American Stroke Association acute ischemic stroke guideline. In patients with acute ischemic stroke due to basilar artery occlusion, prestroke mRS 0 to 1, NIHSS at least 10, and PC-ASPECTS at least 6, endovascular thrombectomy within 24 hours is recommended to improve functional outcome and reduce mortality (Class 1, Level A). [1]

The guideline keeps lower-severity presentations separate. With basilar occlusion, prestroke mRS 0 to 1, NIHSS 6 to 9, and PC-ASPECTS at least 6, the effectiveness of thrombectomy within 24 hours is not well established (Class 2b, Level B-R). That distinction matters: the positive trials do not support treating the NIHSS spectrum as one continuous evidence category.

For medium or distal posterior cerebral artery occlusion, the same guideline reports no benefit from stent-retriever thrombectomy based on current randomized evidence. Basilar evidence should not be used to override that separate anatomy-specific conclusion.

03

The early randomized evidence was neutral—but not simple {#early-evidence}

BEST

BEST randomized 131 patients with acute vertebrobasilar occlusion within 8 hours at 28 centers in China. The trial stopped early because recruitment was poor and crossover was high. In intention-to-treat analysis, 90-day mRS 0 to 3 occurred in 42% with endovascular therapy and 32% with medical therapy; superiority was not established. [3]

Per-protocol and as-treated estimates favored intervention, but those comparisons no longer preserve randomization after treatment switching. BEST therefore raised a plausible efficacy signal while showing how loss of equipoise and crossover can make a randomized basilar trial difficult to interpret.

BASICS

BASICS randomized 300 patients with imaging-confirmed basilar artery occlusion within 6 hours after a long international recruitment period. Ninety-day mRS 0 to 3 occurred in 44.2% with endovascular therapy and 37.7% with medical therapy (risk ratio 1.18; 95% CI 0.92 to 1.50), so superiority was not established and the confidence interval did not exclude a meaningful benefit. [4] [5]

Nonconsecutive enrollment, treatment of eligible patients outside the trial, protocol evolution, prolonged recruitment, and later inclusion of milder deficits all affected interpretation. BASICS was not evidence that thrombectomy never works; it was evidence that a broad, slowly enrolled trial had not yet identified a clear randomized treatment effect.

What the early trials taught

BEST and BASICS differed in anatomy, geography, time window, background treatment, severity, crossover, and enrollment behavior. Their neutral intention-to-treat results justified stronger trials. They did not justify combining their per-protocol signals into proof, nor did they establish futility.

04

Later positive trials changed the guideline {#positive-trials}

ATTENTION: selected patients within 12 hours

ATTENTION randomized 340 adults in China in a 2:1 ratio to thrombectomy plus best medical care or best medical care alone. Entry required imaging-confirmed basilar occlusion within 12 hours, NIHSS at least 10, and age-dependent PC-ASPECTS criteria intended to limit extensive baseline injury.

At 90 days, mRS 0 to 3 occurred in 46% with thrombectomy and 23% with medical care (adjusted rate ratio 2.06; 95% CI 1.46 to 2.91). Mortality was 37% versus 55%. Symptomatic intracranial hemorrhage occurred in 5% versus 0%, and procedural complications occurred in 14%. [6]

ATTENTION established a clear randomized benefit in selected moderate-to-severe basilar occlusion. It did not establish equivalent benefit in mild deficits, extensive posterior injury, substantial prestroke disability, or every non-Chinese workflow and disease-mechanism distribution.

BAOCHE: selected patients from 6 to 24 hours

BAOCHE tested a different population. It randomized patients 6 to 24 hours after onset or last-known-well, with prestroke mRS 0 to 1, PC-ASPECTS at least 6, and limited brainstem injury. The NIHSS threshold was initially at least 10 and later expanded to at least 6; only 17 randomized patients had NIHSS 6 to 9.

Among 217 analyzed patients, 90-day mRS 0 to 3 occurred in 46% with thrombectomy and 24% with medical therapy (adjusted rate ratio 1.81; 95% CI 1.26 to 2.60). Symptomatic intracranial hemorrhage occurred in 6% versus 1%, mortality in 31% versus 42%, and procedural complications in 11%. The trial stopped early for efficacy. [7]

BAOCHE established late-window benefit in a selected population; it did not provide a robust randomized estimate for NIHSS 6 to 9. Endpoint and eligibility changes, early stopping, nonconsecutive enrollment, outside-trial treatment, low thrombolysis use, sex imbalance, Chinese geography, and atherothrombotic predominance all affect generalizability.

Why ATTENTION and BAOCHE should not be blended

ATTENTION and BAOCHE point in the same direction but answer different questions:

• ATTENTION enrolled within 12 hours; BAOCHE enrolled from 6 to 24 hours.
• ATTENTION required NIHSS at least 10; BAOCHE later allowed NIHSS 6 to 9 but enrolled very few such patients.
• Their age rules, imaging thresholds, onset definitions, randomization ratios, endpoints, stopping behavior, and background thrombolysis differed.
• Both were conducted in China, where intracranial atherosclerosis and care pathways may differ from other populations.

The practice effect is concordant randomized evidence for selected basilar occlusion—not a single hybrid eligibility checklist assembled from whichever criterion is most permissive in each trial.

05

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

• Selected basilar occlusion with NIHSS at least 10: thrombectomy within 24 hours is now guideline-recommended when prestroke mRS is 0 to 1 and PC-ASPECTS is at least 6.
• NIHSS 6 to 9: clinical concern may still be substantial, but randomized effectiveness is not well established; this remains a separate evidence category.
• Posterior injury matters: PC-ASPECTS and brainstem involvement are not interchangeable with anterior-circulation ASPECTS or perfusion-core selection.
• Do not delay unnecessarily: the 24-hour boundary is not evidence that time is unimportant.
• Do not extrapolate by territory: positive basilar trials do not establish benefit for isolated vertebral, posterior cerebral, or other medium/distal posterior occlusions.

06

Unresolved selection and generalizability gaps {#evidence-gaps}

Important gaps remain for:

• NIHSS 6 to 9, including fluctuating low-severity presentations followed by deterioration;
• extensive posterior-circulation or brainstem injury;
• prestroke disability beyond mRS 1;
• women, who were underrepresented in BAOCHE;
• non-Asian populations and embolic mechanisms;
• systems with different transfer, thrombolysis, device, rescue-angioplasty, or intracranial-atherosclerosis practices;
• outcome measures that better capture posterior-specific disability and quality of life; and
• non-basilar posterior-circulation occlusions.

Practical CTA, CTP, MRI, collateral-score, or device-technique interpretation is outside this article. Trial criteria should inform judgment, not be recombined into an uncited institutional protocol.

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07

Education-only boundary {#education-only}

This is an evidence-to-practice educational review. It does not replace local stroke-system procedures, multidisciplinary assessment, transfer agreements, device instructions, 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. Lim N-A, et al. Functional and Mortality Outcomes with Medical and Surgical Therapy in Malignant Posterior Circulation Infarcts: A Systematic Review. J Clin Med. 2023;12:3185. doi:10.3390/jcm12093185
3. Liu X, Dai Q, Ye R, et al; BEST Trial Investigators. Endovascular treatment versus standard medical treatment for vertebrobasilar artery occlusion (BEST): an open-label, randomised controlled trial. Lancet Neurol. 2020;19:115-122. doi:10.1016/S1474-4422(19)30395-330395-3)
4. Langezaal LCM, van der Hoeven EJRJ, Mont'Alverne FJA, et al; BASICS Study Group. Endovascular Therapy for Stroke Due to Basilar-Artery Occlusion. N Engl J Med. 2021;384:1910-1920. doi:10.1056/NEJMoa2030297
5. van der Hoeven EJRJ, Schonewille WJ, Vos JA, et al; BASICS Study Group. The Basilar Artery International Cooperation Study (BASICS): study protocol for a randomised controlled trial. Trials. 2013;14:200. doi:10.1186/1745-6215-14-200
6. Tao C, Nogueira RG, Zhu Y, et al; ATTENTION Investigators. Trial of Endovascular Treatment of Acute Basilar-Artery Occlusion. N Engl J Med. 2022;387:1361-1372. doi:10.1056/NEJMoa2206317
7. Jovin TG, Li C, Wu L, et al; BAOCHE Investigators. Trial of Thrombectomy 6 to 24 Hours after Stroke Due to Basilar-Artery Occlusion. N Engl J Med. 2022;387:1373-1384. doi:10.1056/NEJMoa2207576

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. Lim N-A, et al. Functional and Mortality Outcomes with Medical and Surgical Therapy in Malignant Posterior Circulation Infarcts: A Systematic Review. J Clin Med. 2023;12:3185.
3. Liu X, Dai Q, Ye R, et al; BEST Trial Investigators. Endovascular treatment versus standard medical treatment for vertebrobasilar artery occlusion (BEST): an open-label, randomised controlled trial. Lancet Neurol. 2020;19:115-122.
4. Langezaal LCM, van der Hoeven EJRJ, Mont'Alverne FJA, et al; BASICS Study Group. Endovascular Therapy for Stroke Due to Basilar-Artery Occlusion. N Engl J Med. 2021;384:1910-1920.
5. van der Hoeven EJRJ, Schonewille WJ, Vos JA, et al; BASICS Study Group. The Basilar Artery International Cooperation Study (BASICS): study protocol for a randomised controlled trial. Trials. 2013;14:200.
6. Tao C, Nogueira RG, Zhu Y, et al; ATTENTION Investigators. Trial of Endovascular Treatment of Acute Basilar-Artery Occlusion. N Engl J Med. 2022;387:1361-1372.
7. Jovin TG, Li C, Wu L, et al; BAOCHE Investigators. Trial of Thrombectomy 6 to 24 Hours after Stroke Due to Basilar-Artery Occlusion. N Engl J Med. 2022;387:1373-1384.