What is Vertebrobasilar Insufficiency?
Vertebrobasilar insufficiency (VBI) is a condition characterized by reduced blood flow through the vertebral and basilar arteries that supply the posterior circulation of the brain, resulting in transient ischemia of the brainstem, cerebellum, and posterior cerebral hemispheres. 1, 2
Pathophysiology and Mechanisms
VBI results from compromised perfusion in the posterior cerebral circulation through two primary mechanisms 1, 2:
- Atherosclerotic stenosis most commonly affects the proximal (first) portion of the vertebral arteries or extends from plaques at the vertebral artery origins as they arise from the subclavian or brachiocephalic arteries 1, 2
- Atheroembolism from vertebral artery plaques can cause brainstem or cerebellar infarction, representing an alternative mechanism beyond simple hypoperfusion 2
- Mechanical compression at the midportion of vertebral arteries can occur when overgrowth of vertebral transverse processes or osteophytes impinge on the artery as it passes through the bony canal, with symptoms provoked by head turning 1, 3
Clinical Presentation
The symptom complex of VBI reflects ischemia to structures supplied by the posterior circulation 1, 3:
- Dizziness and vertigo (most common symptom, accounting for 27.7% of presentations) 4
- Visual disturbances including diplopia, blurred vision, and transient blindness 1, 3
- Ataxia and imbalance 1, 3
- Perioral numbness 1, 3
- Bilateral sensory deficits 1, 3
- Tinnitus 1, 3
- Syncope 1, 3
Important Diagnostic Caveat
These symptoms are nonspecific and can be caused by other disease entities including cardiac arrhythmias, orthostatic hypotension, and vestibular disorders, making differential diagnosis essential 1, 3. Recent evidence suggests that VBI manifests with at least 37 different symptoms either in isolation or combination, challenging the traditional reliance on Coman's 5 D's (dizziness, diplopia, drop attacks, dysarthria, dysphagia) which account for only 22% of reported features 4.
Epidemiology and Clinical Significance
- Vertebral artery atherosclerosis is the causative basis for approximately 20% of posterior circulation strokes 1, 5, 3
- Annual stroke rates for patients with symptomatic intracranial vertebral and basilar artery stenosis are 8% and 11%, respectively 1, 3
- Vertebrobasilar arterial stenosis is associated with multiple ischemic episodes and higher risk of early recurrent stroke compared to carotid territory disease 1, 5
- Like carotid atherosclerosis, VBI patients face increased risk of other cardiovascular ischemic events including myocardial infarction and peripheral arterial disease 3
Anatomical Considerations
The vertebrobasilar system has important anatomic variations 1, 5, 2:
- Vertebral arteries typically arise from subclavian arteries, but in approximately 5% of individuals the left vertebral artery arises directly from the aortic arch 1, 5, 2
- Each vertebral artery has four segments (V1-V4), with the first three being extracranial 1, 5, 2
- Anatomic variants are more common than in the carotid circulation, requiring careful consideration during clinical assessment and treatment planning 1, 5, 2