Vertebrobasilar Insufficiency (VBI)

How the vertebrobasilar system works

Two vertebral arteries run up through the bones of the neck and join inside the skull to form the basilar artery. Together they make up the posterior circulation, which supplies about one-fifth of the brain's blood. They feed the brainstem (which controls breathing, swallowing, eye movement and alertness), the cerebellum (coordination and balance), the inner ear, and the occipital lobes (vision).

When a vertebral or basilar artery narrows, blood flow can fall below what these areas need, especially when blood pressure drops. The result is short, temporary episodes of brainstem symptoms. If flow stops long enough, brain cells die and a posterior circulation stroke occurs. About 20 to 25% of ischemic strokes affect this territory.

Vertebrobasilar insufficiency symptoms

Symptoms come on suddenly and usually last minutes. They often appear in combination, which separates VBI from simple dizziness:

• Vertigo or dizziness: a spinning or swaying feeling, often with nausea
• Double vision or blurred vision, or loss of vision in part of the visual field in both eyes
• Unsteadiness and poor coordination (ataxia): staggering, veering to one side, clumsy hands
• Slurred speech (dysarthria) and difficulty swallowing
• Numbness or tingling of the face, often around the mouth, or on one or both sides of the body
• Weakness in an arm or leg, sometimes alternating sides between episodes
• Drop attacks: sudden falls from leg weakness without passing out
• Confusion or brief memory loss
• Headache at the back of the head

Causes of vertebrobasilar insufficiency

Atherosclerosis

The leading cause is atherosclerosis, the buildup of cholesterol plaque in artery walls. Plaque narrows the vertebral artery where it starts from the subclavian artery, or along the basilar artery. Small clots can also form on the plaque and travel downstream.

Embolism from the heart

Clots that form in the heart, most often because of atrial fibrillation, can travel to the posterior circulation and block an artery.

Vertebral artery dissection

A tear in the inner wall of a vertebral artery, called vertebral artery dissection, is a leading cause of posterior stroke in people under 50. It can follow neck trauma, sudden neck twisting, vigorous sports or neck manipulation, or happen without obvious cause. It usually starts with one-sided neck or back-of-head pain.

Subclavian steal syndrome

Narrowing of the subclavian artery before the vertebral artery branches off can make blood flow backward down the vertebral artery when the arm is exercised. Subclavian steal syndrome causes dizziness or visual symptoms during arm use, and a blood pressure difference of more than 15 to 20 mmHg between the arms.

Bony compression (bow hunter's syndrome)

Rarely, turning the head compresses a vertebral artery against bone spurs from cervical spondylosis, causing symptoms only in certain head positions.

Risk factors

• Age over 60
• High blood pressure, the single biggest modifiable factor
• Diabetes
• Smoking
• High LDL cholesterol
• Coronary heart disease or peripheral artery disease
• Male sex
• Sleep apnea and chronic kidney disease

How vertebrobasilar insufficiency is diagnosed

Because episodes are often over by the time you see a doctor, the history is vital. Describe exactly what happened, how long it lasted and what you were doing. Doctors then:

1. Examine the nervous system: eye movements, coordination, gait, speech, strength and sensation. They measure blood pressure in both arms.
2. MRI of the brain with diffusion-weighted imaging: the best test for small posterior strokes. CT scans often miss them.
3. Image the arteries: CT angiography or MR angiography shows narrowing, blockage or dissection. Duplex ultrasound can assess the vertebral arteries in the neck but sees only part of their course.
4. Look for a heart source: an ECG, heart rhythm monitoring and an echocardiogram.
5. Blood tests: cholesterol, blood sugar (HbA1c), kidney function and a full blood count.

Telling VBI apart from inner ear vertigo

Treatment

Treatment aims to prevent a stroke and depends on the cause.

Medicines

• Antiplatelet therapy: aspirin, clopidogrel or a short course of both after a recent TIA or minor stroke, as decided by your doctor.
• Anticoagulants if atrial fibrillation is the cause.
• High-intensity statin to lower LDL cholesterol and stabilize plaque.
• Blood pressure medicines to reach target, usually below 130/80 mmHg after a TIA or stroke.

Lifestyle changes

Stopping smoking, controlling diabetes, regular physical activity, limiting alcohol, and losing weight if needed all reduce the risk of further events.

Procedures

Stenting of a narrowed vertebral or basilar artery is reserved for selected people whose symptoms continue despite the best medical treatment, because trials have not shown a clear benefit over medicines alone for most patients. Bypass surgery or decompression is used for rare problems such as subclavian steal or bow hunter's syndrome.

Outlook

The risk of stroke is highest in the days and weeks after a first posterior TIA, which is why fast assessment matters. With prompt antiplatelet treatment, cholesterol and blood pressure control, many people have no further episodes. Untreated basilar artery narrowing carries a significant risk of severe brainstem stroke.

Frequently asked questions

What are the symptoms of vertebrobasilar insufficiency?

Typical symptoms are sudden vertigo, double vision, unsteadiness, slurred speech, trouble swallowing, numbness of the face or limbs, weakness and drop attacks. They usually last minutes and come in combinations rather than alone.

What causes vertebrobasilar insufficiency?

Most cases are caused by atherosclerosis narrowing the vertebral or basilar arteries. Other causes include clots from the heart in atrial fibrillation, vertebral artery dissection, subclavian steal syndrome and, rarely, compression of the artery by neck bone spurs when turning the head.

Is vertebrobasilar insufficiency a stroke?

Not exactly. VBI episodes are temporary drops in blood flow without permanent damage, so they behave like transient ischemic attacks. They are a strong warning sign that a stroke may follow, so they need urgent medical assessment and treatment.

Can vertebrobasilar insufficiency be cured?

The narrowing itself rarely reverses, but its effects can be controlled. Antiplatelet medicine, statins, blood pressure control and stopping smoking greatly reduce the risk of further episodes and stroke. A stent or surgery helps a small number of people.

Can neck movements cause vertebrobasilar insufficiency?

Rarely. In bow hunter's syndrome, turning the head compresses the vertebral artery. Sudden neck twisting or manipulation can also tear the artery (dissection). Most dizziness with head movement, though, comes from the inner ear, not the arteries.

Is vertebrobasilar insufficiency the same as vertebrobasilar artery insufficiency?

Yes. Both terms describe reduced blood flow through the vertebral and basilar arteries. Doctors increasingly use "posterior circulation TIA or stroke" for the same problem.