ISCHEMIC STROKE / PREVENTION

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%
- the risk is even higher in the presence of impaired VMR [Vernieri, 1999]
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

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