ISCHEMIC STROKE / PREVENTION

Extracranial-intracranial bypass

• ICA occlusion is responsible for ~15-25% of strokes
• ICA occlusion is associated with a 2-year stroke risk of about 10-15% (according to other sources, the risk is 5-20% per year) (Powers, 2011)
  • the risk is even higher in the presence of impaired VMR  [Vernieri, 1999]
• extracranial-intracranial (EC-IC) arterial bypass surgery has been developed to prevent stroke by improving hemodynamics distal to the occluded artery
  • for patients with symptomatic atherosclerotic ICA occlusion
  • for patients who would not tolerate planned ICA ligation (for surgically inaccessible aneurysms, tumors, etc.) according to balloon test occlusion (BTO)
• studies have not demonstrated the efficacy of EC-IC bypass compared to conservative therapy in secondary stroke prevention in patients with ICA occlusion, even when using techniques to assess hemodynamic impairment (see COSS trial from 2011)
  • however, COSS confirmed the predictive accuracy of PET OEF for identifying a high-risk subgroup (22.7 % stroke rate at 2 years) and confirmed the hypothesis that improving cerebral hemodynamics in these patients will considerably reduce the risk of subsequent stroke. However, the peri-operative stroke rate nullified the overall benefit of surgery

• EC-IC bypass is not recommended for patients with recent symptomatic ICA/MCA stenosis or occlusion (AHA/ASA 2021  III/A)
• previous guidelines stated that EC-IC bypass may be considered an experimental procedure in patients with symptomatic distal ICA stenosis/occlusion who experience recurrent stroke/TIA despite the best medical therapy (BMT)

• theoretical indications are untreatable ICA stenosis/occlusion or MCA occlusion
• the most commonly performed procedures are:
  • direct anastomosis (vessel to vessel, immediate revascularization, recipient vessel size > 1-1.5 mm)
    • bypass between the superficial temporal artery (STA) and cortical MCA branches
    • ECA-MCA bypass
    • ICA-MCA bypass
  • indirect anastomoses (via the temporal muscle, new capillary network formation is promoted, smaller flow volume)
    • this bypass is typically offered to patients with moyamoya

• can theoretically be offered for otherwise untreatable stenoses and occlusions of the vertebral and basilar arteries
• usually, the connection between the occipital artery and PICA or SCA is established
  • it is possible to create a high-flow bypass using a saphenous vein graft