Vertebrobasilar insufficiency

Vertebrobasilar insufficiency refers to the entire range of symptoms caused by a reduction in blood flow in the posterior cerebral circulation.

Etiologies

Vertebrobasilar stenosis

The mechanism of vertebrobasilar insufficiency is usually hemodynamic, typically associated with atherosclerotic lesions of the vertebral arteries or the basilar trunk (deregulation of distal vertebral and basilar flow, usually in the absence of collateral supply from the carotid territory) or with a heart condition. The presence of orthostatic hypotension should be systematically investigated.

It is sometimes difficult to distinguish true vertebral stenosis from simple anatomical variants. Vertebral arteries are often asymmetrical (the left artery is usually dominant), and approximately 10% of the population has a hypoplastic vertebral artery (++ right) with a diameter of less than 2 mm, which can be mistaken for stenosis or even occlusion.

Subclavian stenosis: subclavian steal syndrome

A stenosis or compression of the subclavian artery (usually on the left, due to anatomical asymmetry) in its pre-vertebral section can lead to subclavian steal syndrome (inversion of ipsilateral vertebral flow), which may include vertebrobasilar insufficiency.

Embolic etiologies

More rarely, the mechanism may be atheroembolic or cardioembolic.

Clinical Presentation and Differential Diagnosis

Vertebrobasilar insufficiency may manifest as episodes of bilateral transient visual loss (amaurosis fugax), although the clinical picture is typically dominated by the occurrence of intermittent vertigo, which becomes progressively more frequent until it is permanent and disabling. Vertebrobasilar strokes may also occur (++ in cases of distal lesions!), as well as drop attacks and syncopal episodes.

In the case of subclavian steal, ischemic manifestations of the ipsilateral arm and/or a decrease in its arterial pulses may sometimes be observed. A very specific positional characteristic: the symptomatology can be triggered by raising the ipsilateral arm (e.g., repetitive effort such as opening and closing the fist in the air).

The differential diagnosis is broad (cardiogenic or vasovagal syncope, epileptic seizures, narcolepsy-cataplexy, psychogenic causes, mechanical anomalies, etc.) and should be adjusted according to the clinical presentation.

Additional Examinations

The evaluation will systematically include:

• Doppler ultrasound of the neck vessels, +/- transcranial
• Brain MRI
• Angio-MRI, angio-CT scan, or angiography of the supra-aortic trunks
• Echocardiography, ECG, ambulatory blood pressure monitoring, and heart rate Holter monitoring

However, there is a significant risk of overdiagnosis of vertebral stenosis (see above). Therefore, diagnosis should be made by comparing the various imaging modalities with the clinical findings.

The differential diagnosis is broad (cardiogenic or vasovagal syncope, epileptic seizures, narcolepsy-cataplexy, psychogenic causes, mechanical anomalies, basilar migraines, etc.) and should be adjusted according to the clinical presentation.

Management and Treatments

In the presence of significant vertebral stenosis or basilar trunk, treatment is usually surgical or endovascular ("interventional"), but the correction of identified lesions has not been proven effective, and the risk of iatrogenic embolic lesions is significant. Depending on the lesion assessment, proximal vertebral revascularization (reimplantation into the posterior cerebral artery) or distal revascularization (bypass with venous graft between the common carotid artery and the vertebral artery in the C1-C2 space) may be considered.

In the case of subclavian steal, treatment depends on the cause:

• Compression: Surgery (tumor resection, resection of a cervical rib, etc.)
• Subclavian stenosis: Surgery (revascularization or bypass), endovascular treatment, or non-interventional management ("conservative treatment": aspirin + statins) to be discussed.

Bibliography

Bradley WG et al., Neurology in clinical practice, 5th ed., Butterworth-Heinemann, e-dition, 2007

Caplan RL, Caplan's Stroke. A clinical approach, 4th ed, Saunders, 2009

EMC, Traité de Neurologie, 2018