Vertebrobasilar insufficiency
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Vertebrobasilar Insufficiency (VBI)
Anatomy
The posterior cerebral circulation (vertebrobasilar system) supplies blood to the brainstem, cerebellum, and occipital lobes via the paired vertebral arteries arising from the subclavian arteries. The vertebral artery has four segments:
- V1 — origin to C6
- V2 — runs within the vertebral foramina to C2
- V3 — above C2 before entering the skull base
- V4 — intracranial portion, joining the contralateral artery to form the basilar artery
Ischemic strokes in the vertebrobasilar territory account for ~25% of all ischemic strokes, with a mortality of 20–30%, significantly higher than anterior circulation strokes.
Etiology & Pathogenesis
Atherosclerosis is the predominant underlying cause. Two mechanisms drive ischemia:
- Low-flow (hemodynamic) — focal stenosis of the subclavian, vertebral, or basilar arteries reduces perfusion. European men tend to have disease at the vertebral artery origin; intracranial atherosclerosis is more common in African Americans, Asians, and women.
- Embolic — up to one-third of VBI episodes result from distal embolization from plaque or mural lesions of the subclavian, vertebral, or basilar arteries. Cardiac and aortic sources also contribute.
Hypertension increases risk through lipohyalinotic thickening of small vessels.
Subclavian steal syndrome is a rarer mechanism: occlusion or stenosis of the subclavian or innominate artery proximal to the vertebral artery origin causes retrograde flow down the vertebral artery to supply the arm, siphoning blood away from the basilar system. Symptoms are triggered by upper-extremity exercise.
Other causes include dissection, trauma, fibromuscular dysplasia (FMD), aneurysms, and Takayasu arteritis.
Clinical Features
Symptoms are typically bilateral and reflect ischemia of the brainstem, cerebellum, and posterior cerebral hemispheres. Presentation with vertigo alone is uncommon (<1% of cases); multiple symptoms usually co-exist:
| Feature | Notes |
|---|---|
| Vertigo | Abrupt onset, usually minutes; most common presenting symptom |
| Diplopia | From cranial nerve or brainstem ischemia |
| Ataxia / disequilibrium | Cerebellar involvement |
| Drop attacks | Without loss of consciousness; precipitated by neck motion — characteristic |
| Headache | Occipital distribution |
| Dysarthria | Brainstem involvement |
| Hemiparesis / hemisensory loss | Contralateral to infarct |
| Visual disturbances | Homonymous hemianopia, visual hallucinations (occipital ischemia) |
| Nausea and vomiting | Via vestibular nuclei |
| Perioral numbness, dysphagia, dysphonia | Cranial nerve involvement |
Repeated episodes of vertigo without any other neurologic symptoms should prompt consideration of an alternative diagnosis (e.g., BPPV, Menière's). — Goldman-Cecil Medicine & Cummings Otolaryngology
Drop attacks from VBI result from transient ischemia of the corticospinal tracts or paramedian reticular formation. They can be an ominous precursor of progressive basilar artery thrombosis, preceding permanent ischemic damage by only hours. — Bradley & Daroff's Neurology
Diagnosis
VBI is commonly misdiagnosed due to vague, overlapping symptoms. The differential includes vasovagal syncope, cardiac arrhythmia, labyrinthine disorders (BPPV, Menière's), migraine with aura, and psychiatric conditions.
Imaging workup:
- CT brain — first step to exclude hemorrhagic stroke (required before thrombolytics)
- MRI brain — often normal between episodes because ischemia is transient; DWI is key during acute events
- MR angiography (MRA) — best non-invasive study; identifies stenosis most commonly at the vertebrobasilar junction
- Duplex ultrasonography (DUS) — useful for proximal vertebral artery disease; can detect reversal of flow indicating subclavian steal; technically more difficult than carotid examination and may miss severe stenosis
- CT angiography (CTA) — alternative to MRA for vascular anatomy
- Conventional angiography — gold standard for surgical planning
Management
Acute Stroke
- Rule out hemorrhage with CT before any thrombolysis
- If within 3 hours of symptom onset: IV t-PA per NINDS guidelines (recommendations are evolving; neurology input is essential)
- Aggressive blood pressure management
Non-Acute / Risk Factor Modification
- Control hypertension, diabetes, and hyperlipidemia — the cornerstone of therapy
- Antiplatelet therapy (aspirin) is the treatment of choice for symptomatic intracranial stenosis (50–99%); warfarin is equally effective but carries higher hemorrhagic risk
- Anticoagulation (warfarin) is considered if the stroke is embolic and cardioembolic in origin
Interventional / Surgical
- Vertebral artery stenting — has been tried with mixed results
- Endarterectomy for extracranial vertebral artery disease — successfully performed; indications still evolving
- Subclavian steal: surgical or endovascular revascularization of the proximal subclavian artery
Key Differentials
| Condition | Key Distinguishing Feature |
|---|---|
| BPPV | Positional nystagmus; no other neurological signs |
| Menière's disease | Low-frequency hearing loss; tinnitus; prolonged attacks |
| Lateral medullary (Wallenberg) syndrome | Ipsilateral Horner's, ipsilateral facial sensory loss, contralateral body sensory loss, dysphagia — a completed stroke |
| Basilar migraine | Young patient; headache; aura mimics VBI |
| Cerebellar infarction | Ataxia + normal head-thrust test; normal MRA rules out VBI |
Sources: Cummings Otolaryngology Head and Neck Surgery; Bradley & Daroff's Neurology in Clinical Practice; Goldman-Cecil Medicine; K.J. Lee's Essential Otolaryngology; Mulholland & Greenfield's Surgery
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