• the vertebrobasilar (VB) system (also called posterior circulation) comprises the subclavian, vertebral, and basilar arteries and their branches; it supplies the cervical spinal cord, brainstem, cerebellum, thalamus, and occipital lobes → anatomy of cerebral arteries
  • posterior circulation is frequently affected by atherosclerosis (AS), although less frequently than the anterior circulation
    • incidence ~ 20-40% of all patients with a cerebrovascular disease
    • atherosclerosis predominantly affects the origin of the vertebral arteries and the V4 segment
  • in addition to atherosclerosis, other conditions may affect perfusion:
  • the most common mechanisms of posterior circulation stroke/TIA include:
    • thromboembolism (resulting from plaque, dissection, or cardioembolism)
    • hypoperfusion (caused by severe stenosis of various etiologies)
    • vasospasm (less common)
Vertebrobasilar territory

Collateral circulation

  • compensatory collateral circulation may occur in the case of proximal stenosis or occlusion of the subclavian and vertebral arteries
    • retrograde flow in the vertebral artery (from the contralateral VA, with or without steal phenomenon in the basilar artery)
    • collaterals from the occipital artery and the thyrocervical trunk
    • steal from a vertebral or mammary artery (with subclavian stenosis/occlusion)
    • collateral retrograde flow from PCA (via PComA) to the basilar artery in case of its proximal occlusion
Extracranial anastomoses in vertebral artery occlusion
Stenosis of the right subclavian artery, occlusion the left subclavian artery, occlusion of V0 segments bilaterally. Collateral circulation comes from the thyrocervical trunk

Clinical presentation

  • asymptomatic stenosis (very common)
    • with/without steal phenomenon (asymptomatic flow alteration in a vertebral artery) on ultrasound
  • weakened pulse and lower blood pressure in the affected limb may be present with significant subclavian artery stenosis
  • transient symptoms of hypoperfusion
  • posterior circulation stroke
    • variable combination of symptoms from the brainstem, thalamus, cerebellum, and occipital and temporal lobes
    • caused by hypoperfusion or thromboembolism
    • transient symptoms (TIA) may precede the infarction

Diagnostic evaluation

Neurosonology

  • a first-line method in the nonacute setting
  • accurate, noninvasive, safe, widely available, and inexpensive
  • useful in combination with CTA/MRA when any invasive procedure is planned
  • assess:
    • B-mode
      • size of the artery (hypoplasia?)
      • search for plaque (composition, stenosis), dissection, thrombus
    • color Doppler
      • flow direction
      • turbulences (aliasing)
    • spectral Doppler
      • waveform
      • velocities
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CT/MR angiography

  • assess all segments of the posterior circulation, starting from the aortic arch
  • CT angiography is preferred, as it provides better visualization of the aortic arch and the origin of the vertebral arteries
Stenosis of the left subclavian artery (CTA)
Subclavian artery stenosis on CTA
Occlusion of the brachiocephalic trunk on CTA

Digital subtraction angiography (DSA)

  • diagnostic DSA has been almost completely replaced by noninvasive imaging techniques
  • DSA has a critical role in interventional neuroradiology; it is frequently used for therapeutic interventions like coiling of aneurysms, arteriovenous malformation (AVM) embolization, thrombectomy, and stenting
Stenosis in the V0 segment of vertebral artery on DSA
Vertebral steal on DSA. Green arrow shows retrograde filling of vertebral artery and subclavian artery

Management

Acute posterior circulation stroke

Stroke prevention

  • patients with symptomatic vertebral stenosis have a higher risk of recurrence than those with carotid stenosis [Flossmann, 2003]
    • prospective studies found a 90-day risk of stroke after vertebrobasilar stroke/TIA of 9.6% in those with vertebrobasilar stenosis and 2.8% in those without, with the highest risk (13.9%) if the stenosis is intracranial (Gulli, 2009)
  • aggressive medical therapy (BMT) is crucial
  • there are no standardized indication criteria for interventions
Best medical treatment

(according to AHA/ASA 2021 1/A)

  • intervention may be suggested for patients with recurrent stroke/TIA despite receiving “best medical therapy”;  the benefit is unknown (AHA/ASA 2021 2b/B-R)
  • indications for intervention include:
    • thromboembolism – stenosis > 50% + more likely cause has been excluded
    • hypoperfusion – stenosis > 70% + contralateral or multiple carotid artery lesions
Angioplasty/stenting
  • robust randomized data demonstrating the superior efficacy of extracranial vertebral angioplasty over conservative management is lacking
    • smaller cohorts show the safety and efficacy of vertebral angioplasty (periprocedural complications 0-3%, success rates up to 94-98%)
    • restenosis occurs in up to 43% of cases, with a maximum occurrence within 12 months after the procedure (though mostly asymptomatic)
  • relatively good results have also been reported for angioplasty of intracranial segments (V4, BA)  [He, 2013]
    • high risk of complication should lead to extreme caution
  • in general, angioplasty is considered for stenoses > 50% when aggressive medical therapy fails; the benefit is uncertain (AHA/ASA 2021 2b/B-R)
Surgery
  • vertebral endarterectomy, vertebral transposition, etc., may be considered when aggressive medical therapy fails, but the benefit is unknown  (AHA/ASA 2021 2b/C-EO)
  • procedures are associated with complications
  • no hard data comparing surgery and angioplasty
Subclavian bypass
  • intervention is generally not recommended in asymptomatic patients  (AHA/ASA 2011 III/C)
    • except for patients in whom the internal mammary artery is planned to be used for myocardial revascularization (to avoid cardiac steal) (AHA/ASA 2011 IIa/C)
  • procedures should be considered mainly in symptomatic patients despite BMT
  • bypass surgery may be offered to symptomatic patients with low perioperative risk if angioplasty is not feasible (AHA/ASA 2011 IIa/B)
    • carotid-subclavian bypass
    • aorta-subclavian bypass

Premedication and periprocedural monitoring are the same as for carotid angioplasty

Subclavian Artery Stenting
Stent in subclavian artery on CTA

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Vertebrobasilar steno-occlusive disease
link: https://www.stroke-manual.com/vertebrobasilar-steno-occlusive-disease/