Can a unilateral vertebral artery stroke cause bilateral vision loss?

Unilateral Vertebral Artery Stroke Can Cause Bilateral Vision Loss

Yes, a unilateral vertebral artery stroke can cause bilateral vision loss through occlusion affecting the posterior circulation that supplies both occipital lobes. 1, 2, 3 This occurs because the vertebral arteries join to form the basilar artery, which then branches into the posterior cerebral arteries that supply both occipital lobes where visual processing occurs.

Anatomical Basis for Bilateral Vision Loss

• The vertebral arteries (left and right) merge to form the basilar artery
• The basilar artery divides into two posterior cerebral arteries (PCAs) that supply:
  • Both occipital lobes
  • Visual cortex bilaterally
• Therefore, a significant occlusion in one vertebral artery can compromise blood flow to both occipital lobes 1, 2

Mechanisms of Bilateral Vision Loss from Unilateral Vertebral Artery Stroke

1. Hemodynamic compromise: When one vertebral artery is occluded and the contralateral vertebral artery is hypoplastic or stenotic, blood flow to both occipital lobes becomes inadequate 1

2. Embolic events: Thromboemboli from a diseased vertebral artery can travel through the basilar artery and lodge in both posterior cerebral arteries 2

3. Anatomical variations: In some patients, both anterior spinal arteries may originate from a single vertebral artery, making bilateral effects more likely with unilateral occlusion 4

Clinical Presentation

Patients with bilateral occipital infarction due to vertebral artery disease typically present with:

• Sudden bilateral vision loss (partial or complete) 1, 3
• Visual field defects, particularly bilateral inferior altitudinal defects 2
• Preserved pupillary light reflexes (distinguishing cortical blindness from retinal causes) 3
• Possible associated symptoms of vertebrobasilar insufficiency:
  • Dizziness, vertigo
  • Diplopia
  • Ataxia
  • Bilateral sensory deficits 5

Risk Factors for Bilateral Vision Loss

Several factors increase the risk of developing bilateral vision loss following a unilateral vertebral artery stroke:

• Advanced age
• General vascular risk factors (hypertension, diabetes, hyperlipidemia)
• History of previous strokes
• Extension of initial infarct to Sylvian border-zone
• Lack of improvement in initial visual field defects 6
• Anatomical variations in the vertebrobasilar circulation 4

Diagnostic Approach

For patients presenting with sudden bilateral vision loss:

1. Neuroimaging:

   • MRA or CTA is recommended rather than ultrasound for evaluation of vertebral arteries 5
   • Diffusion-weighted MRI to detect acute ischemic changes in occipital lobes 3
   • Catheter-based angiography may be necessary to define vertebral artery pathoanatomy when noninvasive imaging is inconclusive 5

2. Additional testing:

   • Evaluate for thrombophilic conditions (as seen in case with MTHFR gene mutation) 3
   • Assess for cardiac sources of emboli

Management

For patients with bilateral vision loss due to vertebral artery stroke:

1. Acute management:

   • Consider thrombolysis if within time window
   • For acute ischemic syndromes with angiographic evidence of thrombus in the vertebral artery, anticoagulation is generally recommended for at least 3 months 5, 7

2. Secondary prevention:

   • Antiplatelet therapy (combination of aspirin plus dipyridamole has shown superior outcomes in vertebrobasilar territory stroke prevention) 7
   • Intensive risk factor modification:
     • Blood pressure control (target <140/90 mmHg)
     • Lipid management with high-intensity statin therapy
     • Diabetes management if applicable
     • Smoking cessation 7

3. Revascularization:

   • Consider angioplasty and stenting for severe vertebral artery stenosis in patients with recurrent symptoms despite optimal medical therapy 1

Prognosis and Visual Rehabilitation

• Some patients may experience visual improvement over time with appropriate management 1
• Visual rehabilitation with prismatic spectacle correction and other optical systems can help maximize remaining vision 2
• Regular follow-up is essential, as patients with unilateral occipital infarction have a 22.4% risk of developing delayed contralateral occipital infarction leading to cortical blindness 6

Key Pitfalls to Avoid

1. Misdiagnosis: Bilateral vision loss may be mistakenly attributed to ocular pathology rather than cerebrovascular disease
2. Incomplete evaluation: Failing to assess both vertebral arteries when only one appears symptomatic
3. Overlooking anatomical variants: Not recognizing that both anterior spinal arteries may originate from a single vertebral artery
4. Delayed treatment: Not recognizing the urgency of posterior circulation strokes

Regular neurological assessments and vascular imaging surveillance are essential for patients with vertebral artery disease to monitor for progression and prevent bilateral vision loss.