Vertebrobasilar Insufficiency

Basics

Vertebrobasilar (VB) vascular system feeds the posterior region of the brain, which includes the brainstem, cerebellum, and inner ear
2 vertebral arteries (VA) derive from subclavian arteries and give rise to the anterior spinal artery and then join to form the basilar artery
Arteries supplying the brainstem and cerebellum originate from the VB system before it branches into the 2 posterior cerebral arteries (PCA), such that a wide variety of focal neurologic deficits arise from VB circulatory dysfunction
Vertebrobasilar insufficiency (VBI) results in inadequate perfusion of VB arterial circulation from thrombotic, embolic, or low-flow states

Mechanism:
- Thrombosis:
  - VB ischemia due to underlying VB atherosclerosis and clot formation
- Embolus:
  - VB ischemia due to embolization of clot from proximal location
- Low-flow states:
  - Hypoperfusion of VB system from systemic (e.g., cardiogenic shock) or localized (e.g., subclavian steal) reduction in blood flow
- Less common etiologies:
  - Fibromuscular dysplasia
  - Hypercoagulable states
Ischemic mechanisms causing VB insufficiency can herald and lead to VB territory infarcts
Severe episodes of VB hypoperfusion or loss of circulation can lead to:
- “Locked-in” syndrome:
  - Quadriplegia (eyelid or eye movement only) with intact consciousness
- “Top-of-basilar” syndrome:
  - Pontine and cerebellar dysfunction with diminished level of consciousness

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