What is the treatment for an M1 (Middle Cerebral Artery) stroke?

Treatment for M1 (Middle Cerebral Artery) Stroke

Endovascular thrombectomy with a stent retriever is the definitive treatment for M1 occlusions, especially within 6 hours of symptom onset, and should be performed in conjunction with intravenous thrombolysis when eligible. 1

Initial Assessment and Imaging

1. Immediate imaging protocol:

   • Non-contrast CT to rule out hemorrhage and estimate ischemic core using ASPECTS
   • Multiphase CT angiography to detect occlusion location, estimate collateral flow, and plan treatment 1

2. Time considerations:

   • Treatment benefit is greatest within 6 hours of symptom onset
   • Beyond 6 hours, advanced imaging (CT perfusion or MRI diffusion/perfusion) may help select patients who could still benefit 1

Treatment Algorithm

First-line therapy (within 4.5 hours of onset):

• Intravenous thrombolysis with r-tPA for eligible patients
• Do not wait to observe response to IV r-tPA before proceeding to endovascular therapy 1

Definitive treatment:

• Endovascular thrombectomy for patients with:
  • M1 occlusion confirmed on imaging
  • NIHSS score ≥6 (functionally relevant deficit)
  • Treatment can be initiated within 6 hours of symptom onset 1

Technical considerations:

• Stent retrievers are the preferred thrombectomy devices (achieved 81.5-95% successful recanalization in clinical trials) 1
• Transradial approach may offer advantages over transfemoral approach including:
  • Shorter reperfusion time (34.1 vs 43.6 minutes)
  • Higher rates of complete reperfusion (TICI 2C or better)
  • Lower rates of symptomatic intracerebral hemorrhage 2

Evidence Quality and Outcomes

The evidence supporting endovascular thrombectomy for M1 occlusions is robust:

• Multiple randomized clinical trials (MR CLEAN, ESCAPE, SWIFT PRIME, EXTEND-IA, REVASCAT) demonstrated significant benefit 1
• Absolute difference of 13.5% in functional independence rates favoring intervention (32.6% vs 19.1%) 1
• M1 occlusions specifically showed better outcomes with thrombectomy compared to medical management alone 1

Important Considerations

1. Location matters: Proximal M1 occlusions (involving lenticulostriate perforators) have worse outcomes than distal M1 occlusions, despite similar recanalization rates 3

2. Time is brain: Benefit declines rapidly with time - MR CLEAN data showed benefit was no longer statistically significant if reperfusion occurred after 6 hours 19 minutes 1

3. Anatomical precision: Accurate identification of M1 vs M2 segments is crucial for treatment decisions and predicting outcomes 4

4. Tandem lesions: When M1 stroke is accompanied by ipsilateral internal carotid artery stenosis/occlusion, treatment of both lesions may be necessary 5

Pitfalls to Avoid

1. Delaying treatment: Do not wait to see if IV thrombolysis works before proceeding to thrombectomy

2. Overreliance on perfusion imaging: While helpful beyond 6 hours, CT perfusion is subject to technical failures in up to 30% of patients and should not delay treatment within the 6-hour window 1

3. Excluding patients based solely on imaging: Even patients with apparent large ischemic cores may benefit from thrombectomy, especially within the early time window 1

4. Missing tandem lesions: Always evaluate the entire cerebrovascular system from aortic arch to vertex to identify potential proximal sources of occlusion 5

The treatment of M1 occlusions requires rapid assessment, imaging, and intervention at centers capable of delivering both IV thrombolysis and endovascular thrombectomy, with outcomes strongly dependent on time to reperfusion.