Vertebral artery occlusion is a medical condition characterized by a blockage or significant narrowing within one or both of the vertebral arteries. These two arteries travel up the neck and merge at the base of the brain, forming a unified circulatory system. The occlusion compromises the blood supply to the posterior region of the brain, an area responsible for many involuntary and coordinated functions. This disruption of flow can lead to severe neurological injury if not quickly addressed.
The Arterial System and Consequences of Occlusion
The two vertebral arteries ascend through the neck vertebrae before uniting within the skull to form the single basilar artery. This collective network, known as the vertebrobasilar system, nourishes the posterior portion of the brain. The primary structures dependent on this blood flow are the brainstem and the cerebellum, which regulate many basic life functions.
The brainstem acts as the relay center connecting the cerebrum to the spinal cord, controlling autonomic functions such as breathing, heart rate, and consciousness. The cerebellum, situated beneath the cerebrum, coordinates voluntary movements, posture, balance, and motor learning. When an occlusion occurs, the resulting lack of oxygen and nutrients to these areas can cause a posterior circulation stroke or a transient ischemic attack (TIA).
A reduction in blood flow to the brainstem can immediately impair regulatory functions, leading to instability in respiration or heart rhythm. Cerebellar damage due to ischemia severely affects the body’s ability to maintain equilibrium and execute coordinated actions. This anatomical relationship establishes why a blockage in the vertebral artery is a high-risk event with the potential for devastating neurological consequences.
Underlying Causes and Risk Factors
The most frequent cause of vertebral artery occlusion is atherosclerosis, which involves the progressive accumulation of plaque (fatty deposits, cholesterol, and cellular waste) within the arterial walls. This plaque hardens and narrows the vessel, a process called stenosis, eventually reducing blood flow or leading to the formation of a clot that completely blocks the artery. This narrowing is often a systemic process, meaning the same disease mechanism occurs in other arteries throughout the body.
Another cause, particularly in younger individuals, is arterial dissection—a tear in the inner lining of the vertebral artery wall. This tear allows blood to seep between the layers, causing the vessel to swell and block the main channel, or creating a surface where a clot can form. Dissections can occur spontaneously or result from mechanical stress, such as hyperextension of the neck, chiropractic manipulation, or blunt trauma.
Occlusion can also be caused by an embolism, which is a piece of foreign material, often a blood clot, that travels through the bloodstream and lodges in the vertebral artery. These emboli typically originate from the heart, often due to conditions like atrial fibrillation where blood pools and clots. Less commonly, a clot may break off from plaque in a larger artery, such as the carotid artery, and travel into the vertebral artery system.
Several systemic conditions increase the likelihood of developing these occlusive mechanisms. Uncontrolled hypertension (high blood pressure) and hypercholesterolemia (high cholesterol) accelerate the formation and progression of atherosclerotic plaques. Diabetes also damages the inner lining of blood vessels, making them more susceptible to disease, and chronic tobacco smoking increases the rate of atherosclerosis. A history of neck trauma or connective tissue disorders can predispose an individual to arterial dissection.
Recognizing the Clinical Symptoms
Compromised blood flow through the vertebrobasilar system results in a distinct set of neurological symptoms, reflecting the functional roles of the brainstem and cerebellum. Vertigo, a severe and often debilitating sensation of spinning or whirling, is one of the most common complaints, stemming from ischemia in the brainstem’s balance centers. This differs from simple lightheadedness and is frequently accompanied by nausea and vomiting.
Another sign is ataxia, which manifests as a lack of muscle coordination and an unsteady gait. Because the cerebellum coordinates movement, reduced blood supply leads to difficulty walking, loss of fine motor control, and inability to maintain posture. Patients may also experience visual disturbances, such as diplopia (double vision), as the brainstem controls the cranial nerves responsible for eye movement.
Ischemia affecting cranial nerve nuclei in the brainstem can lead to problems with communication and swallowing. This presents as dysarthria, or slurred and unclear speech, and dysphagia (difficulty moving food and liquids). These symptoms indicate damage to the areas governing the muscles of the mouth, tongue, and throat.
A symptom is the “drop attack,” where an individual suddenly collapses without loss of consciousness. This event is caused by temporary ischemia to the motor control centers in the brainstem, leading to a transient loss of muscle tone in the limbs. The combination of these specific symptoms—vertigo, ataxia, and cranial nerve deficits—points toward insufficiency in the posterior circulation.
Confirmatory Diagnostic Procedures
Medical professionals employ various imaging techniques to confirm and characterize vertebral artery occlusion. Magnetic Resonance Angiography (MRA) is a non-invasive procedure that uses magnetic fields and radio waves to generate detailed images of the blood vessels. MRA provides excellent visualization of the vertebral artery lumen and identifies the location of the blockage or severe stenosis without the need for an invasive catheter.
Computed Tomography Angiography (CTA) is another non-invasive method that uses X-rays and an injected contrast dye to produce cross-sectional images of the arteries. CTA is useful in the acute setting because it is fast and can visualize the vertebral artery, often showing calcification or plaque, and help differentiate between a blockage and an arterial dissection. Both MRA and CTA are used to assess the collateral circulation, which is the network of smaller vessels that may be compensating for the blocked artery.
Doppler ultrasound, specifically Transcranial Doppler (TCD), uses high-frequency sound waves to measure the speed and direction of blood flow within the vertebral arteries. This technique can non-invasively detect reduced flow velocity, turbulent flow patterns, or the absence of flow, which are indirect signs of occlusion or high-grade stenosis. TCD is used for initial screening and for monitoring the status of the arteries over time.
The most detailed, though invasive, method is conventional catheter angiography. A thin tube is guided through the arteries to the neck, and a contrast agent is injected directly into the vertebral artery. This provides a real-time, high-resolution roadmap of the vessel, considered the gold standard for defining the anatomy and severity of the lesion. Catheter angiography is typically reserved for cases where non-invasive tests are inconclusive or when an endovascular intervention, such as stenting, is planned.
Acute and Long-Term Management
The acute management of vertebral artery occlusion, especially when it results in an ischemic stroke, focuses on rapidly restoring blood flow to salvage brain tissue. For eligible patients presenting within a specific time window, intravenous thrombolytic agents, such as tissue plasminogen activator (tPA), may be administered to dissolve the clot. When the occlusion is caused by a large clot, a mechanical thrombectomy procedure may be performed to physically remove the clot.
Once the immediate threat to the brain has been addressed, long-term management centers on preventing future occlusive events. Antiplatelet medications, such as aspirin or clopidogrel, are commonly prescribed to make blood cells less likely to clump together and form new clots. If the occlusion was caused by a clot originating from the heart, anticoagulant therapy, which interferes with the blood clotting cascade, may be initiated.
A fundamental component of prevention involves rigorous control of vascular risk factors. This includes managing hypertension through medication and diet, lowering cholesterol levels with statin drugs, and controlling blood sugar in patients with diabetes. Lifestyle modifications, such as smoking cessation, regular physical activity, and a healthy diet, are encouraged to slow the progression of atherosclerosis.
For patients with severe stenosis or recurrent symptoms despite medication, revascularization procedures may be considered. Endovascular stenting involves placing a mesh tube within the narrowed artery to prop it open and improve blood flow. In rare cases, open surgical options like a bypass procedure may be performed to create a new pathway for blood to flow around the blocked segment.