What is the clinical significance of a left persistent trigeminal artery (PTA) with non-visualization of the basilar artery on Magnetic Resonance Angiography (MRA) of the brain?

Clinical Significance of Left Persistent Trigeminal Artery with Non-Visualization of Basilar Artery

This finding represents a critical anatomical variant where the persistent trigeminal artery (PTA) is the dominant or sole blood supply to the posterior circulation, indicating that the basilar artery is either severely hypoplastic or functionally absent—this creates significant risk for posterior circulation ischemia and requires urgent vascular imaging confirmation and aggressive stroke prevention strategies. 1, 2

Understanding the Vascular Anatomy

What This Represents

• The persistent trigeminal artery is the most common embryological carotid-basilar anastomosis to persist into adulthood, occurring in 0.1-0.76% of the population 2, 3
• When the basilar artery is not visualized on MRA in the presence of a PTA, this typically indicates that the PTA has become the primary or exclusive blood supply route from the anterior (carotid) circulation to the posterior circulation 1, 2
• This configuration suggests that the vertebral arteries are hypoplastic or non-contributory, and the basilar artery is either severely hypoplastic or fills only through retrograde flow from the PTA 1, 3

Associated Vascular Abnormalities to Expect

• Hypoplastic or absent ipsilateral posterior communicating artery occurs in most cases with PTA 1
• Hypoplastic vertebral arteries, particularly on the ipsilateral side 1, 3
• The basilar artery distal to the PTA insertion may be hypoplastic or absent 1, 2
• Other cerebrovascular anomalies may coexist, including duplicated cerebellar arteries or anterior circulation variants 1

Clinical Implications and Risk Assessment

Stroke Risk Profile

• This patient faces elevated risk for posterior circulation ischemia through two mechanisms: hypoperfusion and microembolization from the carotid artery directly into the posterior circulation 1
• The annual stroke rate for symptomatic vertebrobasilar disease ranges from 8-11%, though specific data for PTA with basilar hypoplasia is limited 4
• Any compromise to the carotid system (stenosis, dissection, thrombosis) could catastrophically affect posterior circulation perfusion since the PTA serves as the primary supply route 1, 2

Symptoms to Monitor

• Vertebrobasilar insufficiency symptoms including dizziness, vertigo, diplopia, perioral numbness, blurred vision, tinnitus, ataxia, and bilateral sensory deficits 5, 4
• Transient ischemic attacks affecting the posterior circulation 6
• Brainstem or cerebellar stroke symptoms 5, 4

Diagnostic Confirmation and Further Workup

Immediate Imaging Considerations

• The non-visualization of the basilar artery on MRA may represent either true anatomical absence/severe hypoplasia OR a technical limitation of time-of-flight MRA 5
• Contrast-enhanced MRA of the head and neck should be performed to definitively assess basilar artery patency, as it has superior sensitivity (97%) and specificity (98%) compared to non-contrast techniques 5
• Consider CT angiography as an alternative, which has demonstrated 100% sensitivity for vertebrobasilar pathology in some studies 5
• Digital subtraction angiography remains the gold standard if non-invasive imaging is equivocal 5, 2

Complete Vascular Assessment Required

• Evaluate the entire anterior circulation bilaterally, as any carotid stenosis or disease becomes critically important when the PTA is the dominant posterior circulation supply 5, 4
• Assess for vertebral artery origins and patency throughout their course 5
• Document the presence and caliber of posterior communicating arteries 1
• Evaluate for associated aneurysms, which occur with increased frequency in PTA patients 2

Management Strategy

Aggressive Stroke Prevention

• Antiplatelet therapy is mandatory—aspirin plus dipyridamole has demonstrated benefit in reducing vertebrobasilar territory strokes (5.7% vs 10.8% with placebo) 4
• Aggressive atherosclerotic risk factor modification including blood pressure control, statin therapy, diabetes management, and smoking cessation 5, 4
• Target systolic blood pressure should be carefully managed—avoid hypotension that could compromise posterior circulation perfusion through the PTA 5

Surveillance Protocol

• Serial noninvasive imaging of both carotid and vertebrobasilar systems to assess for progression of atherosclerotic disease 4
• Monitor for development of new stenotic lesions in the carotid system, which would have catastrophic implications 5, 4
• Assess for interval development of collateral circulation 5

Surgical and Interventional Considerations

• Any planned carotid intervention (endarterectomy or stenting) requires extreme caution and detailed pre-procedural planning, as the PTA makes the posterior circulation dependent on carotid flow 2
• Neurosurgical procedures in the parasellar region carry increased risk of hemorrhage or ischemia if the PTA is manipulated 7, 2
• Percutaneous trigeminal ganglion procedures are relatively contraindicated 7

Critical Pitfalls to Avoid

Imaging Interpretation Errors

• Do not assume the basilar artery is truly absent based solely on time-of-flight MRA—confirm with contrast-enhanced imaging 5
• MRA has only 77% sensitivity for vertebral artery pathology; CTA or catheter angiography may be needed 5
• Evaluate source images carefully, as flow-related artifacts can mimic vessel absence 5

Clinical Management Errors

• Never treat this as a benign incidental finding—the altered hemodynamics create real stroke risk 1, 6
• Avoid aggressive blood pressure lowering without understanding the patient's cerebral perfusion pressure requirements 5
• Do not perform carotid interventions without full understanding of posterior circulation dependence 2
• Recognize that standard stroke risk stratification tools may underestimate risk in this population 1, 6

Patient Counseling

• Educate the patient about posterior circulation stroke symptoms requiring immediate evaluation 4
• Emphasize the critical importance of atherosclerotic risk factor control 5, 4
• Discuss the need for informing all future healthcare providers about this vascular variant before any head/neck procedures 7, 2