What does a revascularization procedure for someone with moyamoya disease involve?

Revascularization Procedures for Moyamoya Disease

Surgical revascularization for moyamoya disease typically involves either direct bypass, indirect bypass, or combined procedures, with the goal of improving cerebral blood flow and reducing the risk of ischemic stroke. 1

Types of Revascularization Procedures

Direct Revascularization

• Superficial temporal artery to middle cerebral artery (STA-MCA) bypass
  • Creates immediate blood flow to ischemic brain tissue
  • Technically more challenging, especially in children due to small vessel size
  • Provides immediate improvement in cerebral oxygenation 2
  • Mean post-bypass flow rates increase approximately fivefold (from 4.4 mL/min to 22.2 mL/min) 3

Indirect Revascularization

• Encephaloduroarteriosynangiosis (EDAS)
  • Involves placing vascularized tissue (typically the superficial temporal artery with surrounding tissue) on the brain surface
  • Relies on angiogenesis and formation of new collateral vessels over weeks to months
  • Less technically demanding than direct bypass
  • Variations include EDAS with dural inversion, which has shown favorable outcomes with 92.6% of patients having good functional outcomes at 90 days 4

Combined Procedures

• Utilizes both direct and indirect techniques
• May provide both immediate and long-term revascularization benefits

Perioperative Management

Anesthetic Considerations

• Preoperative hydration with intravenous fluids is recommended to maintain adequate blood volume 1
• Arterial line placement before anesthesia induction for continuous blood pressure monitoring
• Maintain systolic blood pressure at or above patient's asymptomatic baseline
• Avoid hypotension, hypovolemia, and hyperthermia 1
• Maintain normocapnia (end-tidal CO2 between 35-45 mmHg) to prevent cerebral vasoconstriction 1
• Avoid mannitol as it can decrease cerebral perfusion pressure 1

Perioperative Complications to Monitor

• Cerebral hyperperfusion syndrome (CHS)
  • Occurs in approximately 16.5% of cases (more common in adults at 19.9% vs. 3.8% in children) 1
  • Manifests as transient neurological deficits (70.2%), hemorrhage (15.0%), or seizures (5.3%)
  • Risk factors include older age, severe preoperative hemodynamic impairment, and longer temporary occlusion time
  • Management includes strict blood pressure control (typically SBP <130 mmHg) 1
• Ischemic events (3.4% risk of perioperative infarction) 4
• Excessive blood flow through bypass may increase risk of complications
  • Flow rates >30 mL/min associated with higher risk of stroke, hemorrhage, and transient deficits 3

Efficacy and Outcomes

• The Japan Adult Moyamoya trial demonstrated that direct bypass reduced rebleeding in hemorrhagic moyamoya (2.7%/year vs 7.6%/year with medical therapy) 1
• For ischemic moyamoya, surgical revascularization is beneficial for patients with cognitive decline or recurrent/progressive symptoms 1
• Long-term outcomes after EDAS with dural inversion show low rates of subsequent ischemic events (5.6%) and hemorrhagic events (1.9%) 4
• Cerebral blood flow monitoring during and after surgery is crucial to confirm adequate revascularization and detect complications 5

Important Considerations and Pitfalls

1. Posterior circulation involvement

   • Progressive posterior cerebral artery stenosis can occur after revascularization in up to 47.4% of cases
   • May cause recurrent ischemic symptoms in approximately 28% of affected patients 6
   • Requires monitoring of posterior circulation after surgery

2. Perioperative cerebral blood flow monitoring

   • Essential to differentiate between ischemia and hyperperfusion, as management strategies are contradictory 5
   • Intraoperative monitoring can confirm bypass patency and effectiveness 2

3. Staged procedures

   • For bilateral disease, procedures are typically staged with 3-6 months between hemispheres
   • Reduces risk of complications from simultaneous bilateral surgery

4. Medical management

   • Antiplatelet therapy (typically aspirin monotherapy) may be reasonable in patients with ischemic moyamoya 1
   • Should not be considered a substitute for revascularization in symptomatic patients

The choice between direct, indirect, or combined revascularization depends on patient factors including age, vessel size, and surgeon expertise, with the goal of optimizing cerebral blood flow and reducing stroke risk.