In a patient with a dominant right vertebral artery and a diminutive left vertebral artery that primarily supplies the posterior inferior cerebellar artery, what is the significance of this circulation pattern for performing a left carotid endarterectomy?

Significance of Vertebral Artery Anatomy for Left Carotid Endarterectomy

This vertebral artery anatomy pattern creates a high-risk scenario for left carotid endarterectomy because the dominant right vertebral artery makes the left carotid system critically important for maintaining adequate cerebral perfusion, particularly if intraoperative hypotension or embolic events compromise posterior circulation flow through the already diminutive left vertebral contribution to the basilar artery. 1

Critical Anatomical Considerations

Your patient has a functionally compromised posterior circulation with:

• Dominant right vertebral artery providing the primary blood supply to the basilar artery 2
• Diminutive left vertebral artery that terminates in PICA with minimal basilar contribution 2
• This creates functional dependence on the right vertebral artery for posterior circulation perfusion 1

The left vertebral artery terminating in PICA (rather than contributing meaningfully to the basilar artery) is present in approximately 3-6% of patients and represents a high-risk anatomical variant. 2, 3

Stroke Risk Implications

The significance for left carotid endarterectomy includes:

• Increased vulnerability to posterior circulation ischemia during carotid cross-clamping if collateral flow through the circle of Willis is inadequate 1, 4
• Higher risk of watershed infarction in the vertebrobasilar territory if systemic hypotension occurs perioperatively 5, 6
• Annual stroke rates for symptomatic vertebral stenosis reach 8%, making the patency of your dominant right vertebral artery critical 7, 1
• Vertebral artery atherosclerosis accounts for approximately 20% of posterior circulation strokes 7

Mandatory Preoperative Assessment

Before proceeding with left carotid endarterectomy, you must:

• Obtain CTA or MRA of the complete circle of Willis to assess anterior communicating artery and bilateral posterior communicating artery patency 1, 4
• CTA/MRA has 94% sensitivity and 95% specificity for vertebral artery evaluation versus 70% for ultrasound 1
• Assess the right vertebral artery for any stenosis or occlusive disease, as this vessel is now the sole meaningful contributor to the basilar artery 1, 2
• Evaluate bilateral carotid arteries to determine degree of stenosis and collateral potential 4

Intraoperative Management Strategy

Selective shunting should be strongly considered during left carotid endarterectomy in this patient because:

• The incomplete posterior circulation makes anterior circulation collaterals more critical 4
• Intraoperative monitoring with EEG or transcranial Doppler can identify inadequate cerebral perfusion during cross-clamping 7
• Maintain mean arterial pressure 20-30% above baseline during cross-clamping to maximize collateral flow 1
• Consider routine shunt placement rather than selective shunting given the compromised posterior circulation anatomy 7

Postoperative Surveillance Requirements

Following left carotid endarterectomy, this patient requires:

• Aggressive atherosclerotic risk factor modification including statin therapy, blood pressure control to target <140/90 mmHg, diabetes management, and smoking cessation 1, 4
• Antiplatelet therapy with aspirin 75-325 mg daily to prevent thromboembolic events 1, 4
• Serial noninvasive imaging with CTA or MRA to monitor the dominant right vertebral artery for progression of atherosclerotic disease 1, 4
• Patient education to recognize posterior circulation ischemia symptoms (dizziness, vertigo, imbalance, diplopia, ataxia) that would indicate compromise of the dominant right vertebral artery 1

Critical Pitfalls to Avoid

• Do not proceed without complete circle of Willis imaging - incomplete collaterals dramatically increase stroke risk during carotid cross-clamping 4
• Do not rely on blood pressure asymmetry alone to assess vertebral artery disease - the left vertebral artery may appear patent but contributes minimally to basilar flow 7, 1
• Do not use ultrasound as the sole imaging modality for vertebral artery assessment - CTA or MRA provides superior visualization of the vertebrobasilar junction 1, 2
• Avoid perioperative hypotension which could precipitate watershed infarction in the posterior circulation territory 5, 6