What are the implications and management of a patient with a diminutive right intramural vertebral artery and a dominant left intramural vertebral artery?

Diminutive Right Intramural Vertebral Artery with Dominant Left Vertebral Artery

A diminutive right intramural vertebral artery with dominant left vertebral artery is a common anatomical variant that typically requires no intervention if asymptomatic, but warrants aggressive medical management of atherosclerotic risk factors and monitoring for posterior circulation symptoms given the increased vulnerability to stroke if the dominant vessel becomes compromised. 1

Clinical Significance

Vertebral artery dominance is a common finding that occurs more frequently on the left side than the right, and anatomical variations are more common in the vertebrobasilar circulation than in the carotid system. 1 This configuration creates a functional dependence on the dominant (left) vertebral artery for posterior circulation perfusion. 2

Stroke Risk Implications

• Vertebral artery atherosclerosis accounts for approximately 20% of posterior circulation strokes, making this anatomical variant clinically relevant. 1, 3
• Vertebral dominance and basilar bending are independent risk factors for brainstem infarction and transient ischemic attack (TIA). 2
• Annual stroke rates for symptomatic intracranial vertebral stenosis reach 8%, emphasizing the importance of the dominant vessel's patency. 1, 3
• The dominant left vertebral artery may cause basilar artery angulation toward the right (recessive) side, potentially affecting hemodynamic flow patterns and increasing vertigo risk. 4

Symptoms to Monitor

Patients should be educated to recognize posterior circulation ischemia symptoms immediately, as these indicate potential compromise of the dominant vessel:

• Dizziness, vertigo, and imbalance (central vestibular symptoms from brainstem compromise) 1, 5
• Diplopia (cranial nerve III, IV, or VI involvement) 5
• Perioral numbness (bulbar ischemia) 5
• Blurred vision or visual field loss (occipital cortex compromise) 5
• Ataxia and incoordination (cerebellar or proprioceptive pathway involvement) 5
• Bilateral sensory deficits (brainstem sensory pathway involvement) 5
• Syncope (severe vertebrobasilar hypoperfusion) 5

Critical caveat: These symptoms can mimic cardiac arrhythmias, orthostatic hypotension, and peripheral vestibular disorders, requiring careful differentiation. 1, 5

Recommended Management Approach

For Asymptomatic Patients:

Medical management following guidelines for carotid artery disease is the standard of care, as no randomized trial evidence supports prophylactic intervention for asymptomatic vertebral artery variants. 1, 3

• Antiplatelet therapy (aspirin or aspirin plus dipyridamole, which reduced recurrent vertebrobasilar strokes from 10.8% to 5.7% compared to placebo) 3
• Aggressive atherosclerotic risk factor modification (hypertension control, statin therapy, diabetes management, smoking cessation) 3
• Serial noninvasive imaging with CTA or MRA to assess progression of atherosclerotic disease in the dominant left vertebral artery and exclude new lesions 1, 3

For Symptomatic Patients:

If posterior circulation symptoms develop, immediate diagnostic evaluation is mandatory:

• CTA or MRA is preferred over ultrasound for vertebral artery evaluation, with 94% sensitivity and 95% specificity versus 70% sensitivity for ultrasound. 1
• Catheter-based angiography may be required before revascularization when noninvasive imaging is inadequate, as neither MRA nor CTA reliably delineates vertebral artery origins. 1
• Transcranial Doppler (TCD) can be useful for hemodynamic assessment, particularly for positional symptoms. 6

Endovascular intervention carries significant risk (5.5% periprocedural neurological complications, 0.3% death risk) and lacks randomized trial evidence of superiority over medical management. 1 Intervention should be reserved for recurrent ischemic symptoms despite optimal medical therapy or progression to preocclusive severity. 1

Key Clinical Pitfalls

• Do not dismiss isolated dizziness or vertigo in patients with this anatomy—these may represent early posterior circulation TIA with 13% subsequent stroke risk within 90 days. 5
• Avoid assuming cervical spine arthritis is the cause of dizziness without excluding vertebrobasilar insufficiency, as both conditions can coexist in older patients. 7
• Recognize that the diminutive right vertebral artery may terminate as a posterior spinal artery and provide no intracranial contribution, making the patient entirely dependent on the left vertebral artery. 8
• Be aware that positional symptoms with head rotation or extension may indicate mechanical compression at the transverse foramina rather than atherosclerotic disease. 1, 6