Extracranial-intracranial bypass

Created 23/09/2022, last revision 19/05/2023

  • ICA occlusion is responsible for ~15-25% of strokes
  • ICA occlusion is associated with a 2-year stroke risk of about 10-15%
  • extracranial-intracranial (EC-IC) arterial bypass surgery was developed to prevent stroke by improving hemodynamics distal to the occluded artery
    • in patients with symptomatic atherosclerotic ICA occlusion
    • in 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 effectiveness of EC-IC bypass compared to conservative therapy in secondary stroke prevention in patients with ICA occlusion; even if techniques assessing hemodynamic impairment are used (see the COSS trial from 2011)
  • EC-IC bypass is not recommended for patients with recent symptomatic ICA/MCA stenosis or occlusion (AHA/ASA 2021  III/A)
  • previous guidelines stated: in patients with symptomatic distal ICA stenosis/occlusion who experience recurrent stroke/TIA despite best medical therapy, EC-IC bypass is considered an experimental procedure.
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EC-IC bypass in carotid territory

  • the theoretical indications are untreatable ICA stenosis/occlusion or MCA occlusion
  • the most commonly performed procedures:
    • 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 temporal muscle, new capillary network formation is promoted, smaller flow volume)
      • this bypass is most commonly offered in patients with moyamoya

EC-IC bypass in posterior circulation

  • theoretical can be offered in otherwise untreatable stenoses and occlusions of 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 graft from the saphenous vein
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
    • stroke recurrence despite aggressive conservative therapy
  • reduced flow in intracranial segments (TCCD shows decreased 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