Direct revascularization procedures

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Vascular bypass

Indications for EC/IC bypass

• Cerebral ischaemia
• Flow augmentation
• EC-IC bypass study
• Not effective preventing ischaemia

• Aneurysms:
• Certain aneurysms are not amendable to either direct microsurgical clipping or endovascular coiling due to
• Extreme size, location, calcification or atherosclerosis, dissection, or the incorporation of perforators or major arteries.
• Bypass + Aneurysm trapping
• EC/IC
• Superficial temporal artery
• Cervical external carotid artery via an interposition graft (Saphenous vein)
• IC/IC
• Radial artery
• Pros
• Eliminating the need for any interposition grafts
• Shortening the bypass length
• Cerebrovascular reserve and need for bypass can be assessed preoperatively using balloon test occlusion (BTO) with hypotensive challenge
• Aneurysms
• Only level Ill evidence available
• Sacrifice of parent vessel or a major branch
• As a temporary measure during prolonged temporary clipping of complex aneurysm
• Aneurysms requiring bypass
• Giant/ blister aneurysms
• Absence of a neck (fusiform or saccular-fusiform) aneurysms
• Severe atherosclerosis or calcification in the neck
• Extensive thrombosis
• Critical branch origin from neck or sac
• Symptomatic dissecting aneurysm
• Blister aneurysm
• Even these are diminishing — flow diverters, bifurcation stents ...
• 4% of aneurysms

• Tumours encasing or invading major arteries

• Cranial base tumours
• Facilitated tumour removal

• Moyamoya disease and moyamoya syndrome
Adult
• Moyamoya
• History of infarct/ hemorrhage/progressive disease
• Do for symptomatic: Haemorrhagic adult moya moya disease (JAM trial)
• Japanese Adult Moyamoya (JAM) trial
• Benefit of direct cerebral revascularization for preventing recurrent bleeds in adults with hemorrhagic moyamoya disease.
• Augment blood flow
• Improvement in CBF has been demonstrated
• Reduction in further ischemic events
• Reduction in hemorrhagic events
• Do not do for: asymptomatic moyamoya disease
• Due to the uncertainty of the natural history of this patient population.
• Regions to be addressed
• MCA : MCA bypass
• ACA territory : multiple burr holes, STA—ACA bypass. vascularized Dural flap
Children
• Symptomatic and progressive moyamoya → surgery as they have poor outcomes without surgery

Pros

• Immediate revascularization

• Better revascularization

Cons

• Perioperative stroke

• Technical challenging

• Moyamoya:
• A higher incidence of symptomatic hyperperfusion with direct revascularization as compared to atherosclerotic disease

Results

• Are superior to indirect revascularization procedures if a donor and recipient vessel of sufficient calibre (≥ 1mm outer dia) can be identified

• May be difficult in the paediatric age group who are the most likely to benefit

• If cannot find sufficient calibre vessel d indirect revascularization procedures

EC/IC Bypass

STA-MCA bypass is the procedure of choice

• Parietal branch preferred (frontal has collaterals with ophthalmic )

• Location of craniotomy
• Junction of the anterior 2/3 and posterior 1/3 of a line joining lateral canthus to ipsilateral tragus
• A line perpendicular to this
• Craniotomy 3-5 cm in diameter 6 cm above this line

• Anastomose to temporal M4 branches
• Avoid ischemia to frontal branches during occlusion
• Good collaterals with PCA
• More consistent good M4 branches

• Outcome

 

STA-ACA bypass

• More difficult and poorer results

Perioperative complications of EC/IC bypass

• Risks of EC/IC bypass include:
• Risk of stroke from temporary occlusion of a cortical vessel,
• Cerebral hyperperfusion
• “Watershed shift” phenomenon with the risk of cerebral hemorrhage from a sharp increase in focal CBF

IC/IC bypass