Plaque formation: Proximal vertebral artery (VA) > distal VA

Grayscale imaging

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  Chronic occlusion: Contracted vessel caliber; VA may be hard to demonstrate

Spectral Doppler

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  Stenosis: Significant focal ↑ in peak systolic velocity (PSV) + poststenotic turbulence or dampened flow

  
  
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  Occlusion: Absent Doppler signals; vertebral venous signals may be prominent

  
  
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  Asymmetrical VA velocities may be due to difference in vessel caliber or unilateral occlusive disease

  
  
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  Mild subclavian steal (SS): Systolic deceleration

  
  
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  Moderate SS: Alternating flow

  
  
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  Complete SS: Flow reversal

  
  
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  Dynamic test with affected arm exercise is recommended to evaluate severity of SS

Color Doppler

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  Stenosis: Aliasing or trickle flow at stenosis

  
  
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  Occlusion: Absent Doppler signals ± surrounding neck collaterals

  
  
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  Mild SS: Antegrade or minimal retrograde flow

  
  
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  Moderate SS: Bidirectional flow

  
  
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  Severe SS: Predominantly retrograde flow

VA hypoplasia, subclavian steal, collateral artery, arteriovenous fistula

Check for presence of intraluminal plaque with abnormal ↑ or ↓ of PSV and neck arterial collaterals

Consider alteration of VA flow velocity, flow asymmetry, and flow resistance as causes for stenosis/occlusion if it cannot be accounted for by VA size

To avoid mistaking musculoskeletal branch of external carotid artery for VA, use transverse process as landmark for identification of VA

Vertebral vein is always anterior to VA