Which intracranial vessels are suitable for thrombectomy?

Intracranial Vessels Suitable for Thrombectomy

Thrombectomy is definitively indicated for large vessel occlusions in both anterior and posterior circulation, with the strongest evidence supporting treatment of the internal carotid artery (ICA), M1 and M2 segments of the middle cerebral artery (MCA), and basilar artery, while smaller distal vessels (M3, M4, P2 and beyond) remain technically feasible but lack robust outcome data.

Anterior Circulation Vessels

Established Indications

• Internal Carotid Artery (ICA): Thrombectomy is indicated for acute ICA occlusions, particularly when associated with tandem intracranial occlusions 1, 2

• Middle Cerebral Artery M1 Segment: This represents the most well-established indication with Class I, Level A evidence for thrombectomy within 6 hours of symptom onset 3

• Middle Cerebral Artery M2 Segment: M2 occlusions are suitable for thrombectomy, with successful recanalization rates of 89% reported using specialized devices designed for smaller caliber vessels (median vessel diameter 1.7 mm) 4

Technical Considerations for Vessel Size

• Vessels as small as 1.5-2.5 mm in diameter can be successfully treated with appropriately sized devices 4
• M3 and M4 segments are technically accessible but lack robust clinical trial data supporting routine intervention 1

Posterior Circulation Vessels

Basilar Artery - Strong Evidence

The basilar artery represents a definitive indication for thrombectomy based on recent landmark trials:

• Within 12 hours: Thrombectomy is recommended (Class I, Level B-R) for patients with NIHSS score ≥6 and PC-ASPECTS ≥6 5
• 12-24 hours: Thrombectomy is reasonable (Class IIa, Level B-R) for patients meeting the same criteria 5
• The ATTENTION trial demonstrated 46% favorable outcomes (mRS 0-3) with thrombectomy versus 23% with medical therapy alone, with mortality reduction from 55% to 37% 1
• The BAOCHE trial confirmed similar benefits (46% vs 24% favorable outcomes) in the 6-24 hour window 1

Vertebral Artery - Limited Evidence

• Vertebral artery occlusions have uncertain benefit with weaker recommendations (Class IIb, Level C) 3
• Thrombectomy may be reasonable in carefully selected patients, but evidence from randomized trials is lacking 3
• The BASICS registry found universally poor outcomes when recanalization was achieved in vertebral artery occlusions with NIHSS ≤6 1

Posterior Cerebral Artery (PCA)

• P1 segment occlusions may be considered for thrombectomy, though evidence is limited 1
• P2 and more distal PCA segments (posterior circulation distal or medium vessel occlusions) lack definitive evidence and remain investigational 1

Critical Vessel Selection Criteria

Imaging Requirements

• CT Angiography (CTA) must demonstrate vessel occlusion 1
• Non-contrast head CT must be free of:
  • Bleeding 1
  • Extensive brainstem infarction (for posterior circulation) 1
  • Cerebellar mass effect 1
  • Acute hydrocephalus 1

Posterior Circulation Scoring

• PC-ASPECTS ≥6 is required for basilar artery occlusion treatment 5
• PC-ASPECTS includes: pons (2 points), cerebellum (1 point per hemisphere), midbrain (2 points), thalamus (1 point per hemisphere), and PCA territory (1 point per hemisphere) 1

Common Pitfalls and Caveats

Avoid These Errors

• Do not delay intravenous thrombolysis while arranging thrombectomy - IV tPA should be administered when eligible, regardless of thrombectomy plans 3
• Do not wait to assess IV tPA response before proceeding to angiography for thrombectomy 3
• Do not assume all large vessels have equal evidence - anterior circulation M1 occlusions have far stronger evidence than isolated vertebral artery occlusions 3

Special Considerations

• Intracranial atherosclerotic disease (ICAD): When underlying ICAD is present, be prepared for rescue angioplasty and stenting - this was performed in 40-55% of cases in the ATTENTION and BAOCHE trials 1, 6
• Distal embolization risk: Mechanical thrombectomy of extracranial ICA without intracranial occlusion carries risk of distal embolization 2
• Reocclusion monitoring: Long-term follow-up imaging is important, as 16.2% of successfully recanalized vessels may develop reocclusion or late stenosis, particularly in MCA occlusions 7

Technical Success Goals

• Target angiographic outcome should be mTICI 2b/3 (modified Thrombolysis in Cerebral Infarction) to maximize probability of good functional outcome 8, 3
• Multiple techniques are effective: aspiration alone (35%), stent retriever alone (5%), or combined approaches (50%) 1