How do you diagnose Vertebrobasilar Insufficiency (VBI)?

Diagnostic Approach to Vertebrobasilar Insufficiency (VBI)

CTA of the head and neck with IV contrast is the recommended initial imaging test for diagnosing vertebrobasilar insufficiency due to its highest reported sensitivity (100%) compared to MRA (77%) and Doppler ultrasound (71%). 1

Clinical Diagnosis of VBI

• VBI is characterized by transient disruption of blood flow in the posterior (vertebrobasilar) circulation, which supplies the thalami, cerebellum, and brainstem 2
• Suspect VBI in patients with chronic recurrent vertigo and associated brainstem neurologic deficits 2
• Common symptoms include dizziness, vertigo, headaches, vomiting, diplopia, blindness, ataxia, imbalance, and weakness on both sides of the body 3
• VBI should be distinguished from other causes of vertigo such as BPPV, migraine-associated vertigo, and central positional vertigo 2
• VBI attacks typically last less than 30 minutes without associated hearing loss 2
• The nystagmus in VBI does not fatigue and is not easily suppressed by gaze fixation, helping differentiate it from peripheral causes 2

Diagnostic Algorithm

Step 1: Clinical Assessment

• Evaluate for risk factors: atherosclerotic disease (most common cause in elderly), vertebral artery dissection, or positional narrowing of vertebral arteries 2
• Note distinguishing features from BPPV: type of nystagmus (typically gaze-evoked in central lesions), severity of postural instability, and presence of additional neurological signs 2

Step 2: Initial Imaging

• CTA head and neck with IV contrast is the preferred initial imaging modality 1
  • Provides excellent evaluation of the course and luminal caliber of vertebral and basilar arteries
  • Can detect luminal filling defects including thrombus, embolus, atherosclerotic plaque, dissection flap, or vascular web 2
  • Ensure imaging includes the entire vertebral artery from origin at the aortic arch to the basilar artery 2

Step 3: Alternative or Additional Imaging

• If CTA is contraindicated, MRA head and neck without and with IV contrast should be used 1
  • High diagnostic performance for vertebral artery origin stenosis (sensitivity 97%, specificity 98%, accuracy 93%) 2
• MRI head without and with IV contrast is valuable for detecting posterior fossa infarcts 1
  • Can identify atherosclerotic plaque and stenosis in the basilar artery
  • Vessel wall enhancement in basilar artery stenosis correlates with risk of subsequent infarct 1

Step 4: Specialized Testing (if diagnosis remains unclear)

• Transcranial Doppler (TCD) can be useful for:
  • Detecting flow abnormalities in the vertebrobasilar circulation 4
  • Monitoring blood flow in symptomatic positions (e.g., head extension) 4
  • Identifying stenosis, occlusion, or steal phenomena in the vertebrobasilar system 5
• Conventional diagnostic angiography may be considered in specific cases:
  • For real-time dynamic evaluation of vessel patency in various neck positions 2
  • When planning surgical revascularization 6
  • Remains the reference standard but carries risks of allergic reactions, renal injury, vascular injury, or complications at access site 2

Important Considerations

• Neuroimaging should not be routinely used in patients with typical BPPV symptoms without additional neurologic signs 2
• The diagnosis of VBI is a clinical challenge because its manifestations are subjective and difficult to quantify 5
• Avoid common pitfalls:
  • Failing to image the entire vertebral artery from origin to basilar junction 1
  • Over-reliance on MRA findings alone 1
  • Vessel wall imaging may overestimate the degree of luminal narrowing 1

Treatment Implications

• Patients with VBI are at higher perioperative risk from revascularization procedures compared to similar lesions in the anterior circulation 2
• If symptomatic patients fail medical management, revascularization of the vertebral artery may be considered through transluminal balloon angioplasty, stent placement, or surgical intervention 6

Remember that each patient with suspected VBI should be evaluated thoroughly, as the condition can lead to significant morbidity and mortality if not properly diagnosed and managed.