Extracranial-intracranial bypass

David Goldemund M.D.
Updated on 26/04/2024, published on 29/12/2022
  • 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)
  • 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)
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EC-IC bypass in carotid territory

  • 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

EC-IC bypass in posterior circulation

  • 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
Theoretical EC-IC bypass candidate
  • proximal vessel occlusion – usually ICA (demonstrated by CTA/ MRA/ DSA)
  • occlusion is symptomatic 
    • e.g. border zone infarcts on brain imaging
    • recurrent stroke despite aggressive conservative therapy
  • reduced flow in intracranial segments (TCCD shows decreased PSV and systolic acceleration)
  • evidence of impaired vasomotor reactivity (TCCD, SPECT) and/or increased O2 extraction fraction (OEF) on PET   → cerebral blood flow regulation

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Extracranial-intracranial bypass