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Which artery block causes stroke?

A stroke occurs when the blood supply to part of the brain is interrupted or severely reduced, depriving brain tissue of oxygen and nutrients. This can be caused by a blockage in an artery leading to the brain or bleeding into the brain tissue. Let’s take a closer look at how artery blockages can lead to stroke.

The role of arteries in stroke

Arteries are blood vessels that carry oxygen-rich blood from the heart to the tissues of the body. The two main arteries that supply blood to the brain are the carotid arteries and the vertebral arteries.

  • The carotid arteries run up either side of the neck and branch off into the internal carotid arteries which enter the cranial cavity and supply blood to the front parts of the brain.
  • The vertebral arteries branch off from the subclavian arteries and join together to form the basilar artery at the base of the brainstem. The basilar artery supplies blood to the brainstem, cerebellum and back parts of the brain.

A blockage in either the carotid or vertebral-basilar arterial systems can impair blood flow to parts of the brain supplied by those arteries. The specific symptoms of stroke depend on which area of the brain is affected.

Carotid artery disease

Carotid artery disease is a major cause of ischemic stroke. This refers to a buildup of plaque – made of fat, cholesterol, calcium and other substances – inside one or both carotid arteries. This is called atherosclerosis and can cause narrowing of the carotid arteries, reducing blood flow to the brain.

If a piece of plaque breaks off it can form a blood clot at the site of the blocked artery. This limits blood supply to parts of the brain fed by that artery, triggering a stroke.

Carotid artery blockages usually occur in the internal carotid artery just after the common carotid artery branches off. A complete blockage here causes severe strokes.

Symptoms of carotid artery blockage

Symptoms of carotid artery disease include:

  • Weakness on one side of the body
  • Numbness on one side of the face or body
  • Slurred speech
  • Vision problems
  • Dizziness or loss of coordination
  • Difficulty swallowing
  • Shortness of breath
  • Paralysis on one side of the body

These are warning signs of a potential stroke. Anyone experiencing them, even temporarily, should seek urgent medical care.

Vertebral and basilar artery disease

Blockages can also occur in the vertebral arteries or the basilar artery at the base of the brain. This disrupts blood flow to the brainstem, cerebellum and occipital lobes at the back of the brain.

Vertebral artery disease is often caused by atherosclerosis. Less common causes include dissection of the artery walls or abnormalities of the cervical spine putting pressure on the vertebral arteries.

Basilar artery stroke is less common but very serious due to the vital functions controlled by the brainstem, such as consciousness, breathing and heart rate.

Symptoms of vertebral/basilar artery blockages

Symptoms may include:

  • Dizziness
  • Vertigo
  • Slurred speech
  • Difficulty swallowing
  • Visual disturbances
  • Loss of coordination
  • Weakness or numbness on one side of the body
  • Loss of consciousness

As with carotid artery blockages, prompt medical treatment is essential if any of these symptoms appear.

Other causes of artery blockages

While atherosclerosis is the most common cause of blocked arteries leading to ischemic stroke, other causes include:

  • Blood clots – Clots can form in the heart due to abnormal heart rhythms like atrial fibrillation. Pieces of clot can break off and travel in the bloodstream to the brain, blocking arteries.
  • Dissections – Tears in the inner artery lining can cause blood clots to form and block blood flow.
  • Inflammation – Arteritis conditions like giant cell arteritis cause inflammation of artery walls.
  • Cervical artery dissection – Tears in the vertebral or carotid arteries in the neck.

Which side artery blockage causes what symptoms?

The symptoms of stroke depend on which side of the brain the blocked artery supplies blood to:

Artery blocked Area of brain affected Potential symptoms
Left carotid artery Right side of brain
  • Right-sided weakness or paralysis
  • Speech problems
  • Vision loss on right side
Right carotid artery Left side of brain
  • Left-sided weakness or paralysis
  • Speech problems
  • Vision loss on left side
Left vertebral artery Right cerebellum and brainstem
  • Dizziness
  • Lack of coordination
  • Double vision
  • Right-sided weakness
Right vertebral artery Left cerebellum and brainstem
  • Dizziness
  • Lack of coordination
  • Double vision
  • Left-sided weakness
Basilar artery Brainstem and cerebellum
  • Dizziness, vertigo
  • Slurred speech
  • Vision loss
  • Weakness or paralysis on one or both sides
  • Loss of consciousness

As seen, blockages on either side of the brain produce different neurologic effects, helping doctors locate the site of the occlusion. Prompt treatment can restore blood flow before permanent brain injury occurs.

Diagnosing artery blockages

If stroke is suspected, medical imaging can locate artery blockages and determine if they are the cause. Tests may include:

  • CT angiography – Contrast dye highlights blood vessels on a CT scan.
  • MRI angiography – MRI technology visualizes blood vessel anatomy.
  • Carotid ultrasound – Soundwaves create images of the carotid arteries.
  • Angiography – Contrast dye is injected into arteries via a catheter to highlight blockages.
  • Transcranial Doppler ultrasound – Measures blood flow in the brain’s arteries.

Finding the location and extent of blockages guides treatment to open up arteries and restore blood supply to the brain tissue at risk.

Treating artery blockages

Treatment depends on the type and location of the blockage:

  • Clot-busting drugs – Medications like tPA can dissolve blood clots if given within 3-4.5 hours of symptom onset.
  • Thrombectomy – A catheter inserted into the artery to physically remove large clots.
  • Carotid endarterectomy – Surgically removing plaque from inside the carotid arteries.
  • Angioplasty and stenting – Opening up a blocked artery with a small balloon or mesh tube.
  • EC-IC bypass – Rerouting blood flow from the external carotid artery to the internal carotid artery.

Rapid treatment is vital to minimize permanent brain damage and disability after stroke. Public awareness of stroke symptoms and calling emergency services at the earliest sign of a problem can improve outcomes.

Prevention of artery blockages

While some risk factors for artery blockages and stroke cannot be changed, such as age, gender and family history, many can be managed through lifestyle changes and medical treatment:

  • Control high blood pressure – a major risk factor for atherosclerosis.
  • Lower cholesterol levels with diet and medication if needed.
  • Manage diabetes to prevent blood vessel damage from high blood sugar.
  • Quit smoking to avoid damaging artery walls.
  • Exercise regularly to boost cardiovascular health.
  • Maintain a healthy weight to avoid obesity-related risks.
  • Follow any prescribed stroke prevention medications, such as blood thinners for atrial fibrillation.

Detecting and treating atherosclerosis risk factors early, before arteries become badly blocked, is key to preventing stroke in at-risk individuals.

Key takeaways

  • Carotid and vertebral/basilar artery blockages are major causes of ischemic stroke.
  • Plaque buildup, blood clots, tears, and inflammation can obstruct these critical arteries supplying the brain.
  • Stroke warning signs like weakness and speech issues should prompt urgent medical attention.
  • CT, MRI, ultrasound, and angiogram imaging locate artery blockages in the brain.
  • Treatments aim to open blocked arteries quickly and restore blood flow to prevent permanent damage.
  • Managing risk factors like hypertension and stopping smoking helps prevent strokes from artery blockages.


Blockages in the major arteries supplying blood to the brain, particularly the carotid and vertebral/basilar arteries, are a leading cause of ischemic strokes. Plaque buildup, clots, tears or inflammation can obstruct these vital blood vessels. Warning symptoms depend on which area of the brain is affected but require prompt treatment. Medical imaging pinpoints artery blockages and guides procedures to open them up and restore blood flow. Controlling cardiovascular risk factors provides important prevention against strokes caused by blocked arteries in the brain.