Vertebral Artery Occlusion: Causes, Symptoms & Treatment

Vertebral artery occlusion occurs when one or both of the vertebral arteries, which run along the back of the neck and feed the brainstem and cerebellum, become blocked by a blood clot, arterial plaque, or a tear in the vessel wall. The consequences range from no symptoms at all, if the other vertebral artery compensates, to devastating posterior circulation stroke affecting balance, vision, swallowing, and consciousness. Because the symptoms often mimic more benign conditions like inner-ear vertigo, posterior circulation strokes are misdiagnosed roughly twice as often as strokes affecting the front of the brain, making this one of the most under-recognized emergencies in medicine.¹

Why the Vertebral Arteries Matter

You have two vertebral arteries, one on each side, that originate from the subclavian arteries near the collarbone and travel upward through small bony canals in the cervical spine before entering the skull. Once inside, they merge into the basilar artery, which supplies the brainstem, cerebellum, and parts of the occipital lobes responsible for vision. Each vertebral artery is typically divided into four anatomical segments, and each segment has its own surgical significance and vulnerability to disease.² The vertebral arteries are often asymmetric: one side is frequently dominant, carrying more blood than the other. That asymmetry matters because when the dominant artery gets blocked, the smaller partner may not pick up the slack.

Atherosclerosis and the Most Common Cause

The single most common reason a vertebral artery narrows or closes is atherosclerosis, the same plaque-buildup process that causes heart attacks and carotid artery disease. Fatty deposits, driven by oxidized LDL cholesterol and inflammation within the arterial wall, gradually thicken and harden the vessel lining.³ The vertebral artery origin, right where it branches off the subclavian artery, is especially prone to plaque. This location is a turbulence zone where blood flow patterns encourage cholesterol accumulation.

The risk factors are familiar: high blood pressure, diabetes, smoking, high cholesterol, and advancing age. What makes vertebral artery atherosclerosis different from carotid disease is that it receives far less clinical attention. Doctors routinely screen the carotid arteries with ultrasound, but the vertebral arteries are harder to visualize and rarely checked until symptoms appear.

Dissection in Younger Adults

In people under 45, the more likely culprit is vertebral artery dissection, a tear in the inner lining of the artery that allows blood to seep between layers of the vessel wall, creating a flap that narrows or blocks flow. Dissection can result from trauma, such as a car accident, sports collision, or forceful neck manipulation, but it also occurs spontaneously with no clear trigger.⁴ The classic story involves a young, otherwise healthy person who develops sudden neck pain and headache, followed hours to days later by stroke symptoms.

When a vertebral artery dissects, brain ischemia occurs in the majority of cases. One large study found that about three-quarters of patients with vertebral artery dissection developed brain ischemia, with about two-thirds suffering a full ischemic stroke and roughly one in ten experiencing a transient ischemic attack.⁵ Spontaneous dissection is typically treated with blood thinners. The damaged artery often heals on its own over weeks to months, though the risk of stroke during the acute period is real and demands prompt recognition.

Less Common Causes

Beyond atherosclerosis and dissection, several other conditions can occlude or narrow the vertebral arteries:

Vertebral artery hypoplasia: Some people are born with one vertebral artery that is abnormally small. This is not a disease in itself, but a meta-analysis found that people with vertebral artery hypoplasia were about twice as likely to have posterior circulation strokes compared to those with normal-caliber arteries, especially when other vascular risk factors were present.⁶ The risk appears to increase with the severity of the hypoplasia, and the smaller artery is more vulnerable to clotting, particularly when atherosclerosis or other prothrombotic factors pile on.⁷
Fibromuscular dysplasia: This non-inflammatory arteriopathy affects medium-sized arteries and can involve the vertebral arteries. It predominantly affects women and may be present in up to seven percent of the population, though most cases are mild and undiagnosed. Hypertension and tobacco use are commonly seen alongside it.⁸
Subclavian steal: When the subclavian artery itself is severely narrowed upstream of where the vertebral artery branches off, blood flow in the vertebral artery can actually reverse direction, stealing supply from the brain to feed the arm. This phenomenon is usually caused by atherosclerosis in the subclavian artery and can produce dizziness and arm fatigue during exercise.⁹¹⁰
Bow hunter syndrome: In rare cases, the vertebral artery gets mechanically pinched during head rotation, typically at the C1-C2 level. It presents mostly in adults aged 50 to 70, and symptoms of vertebrobasilar insufficiency are triggered by turning the head to the side opposite the dominant vertebral artery.¹¹ The name comes from the head-turning posture of an archer. Bony spurs or soft-tissue anomalies in the cervical spine create the compression.¹²

Symptoms That Mimic Other Conditions

The symptoms of vertebral artery occlusion depend on where the blockage sits and how well the collateral blood supply compensates. Many people with chronic vertebral artery narrowing never notice a thing, because the other vertebral artery and connections from the carotid system keep the posterior brain fed. But when flow is insufficient, the symptoms tend to involve the brainstem and cerebellum and can look confusingly like inner-ear problems, migraine, or even anxiety.

The hallmark presentation is Wallenberg syndrome, also called lateral medullary syndrome, which results from infarction of the lateral portion of the medulla. Vertebral artery disease was confirmed by imaging in about three-quarters of patients with this condition in one clinical series.¹³ The most reliable triad for identifying it is Horner syndrome (a droopy eyelid and small pupil on the affected side), incoordination of the same-side arm and leg, and loss of pain and temperature sensation on the opposite side of the body. In that same series, Horner syndrome was found in over 90% of patients, same-side ataxia in 85%, and opposite-side loss of pain sensation in 85%.

Other common symptoms at onset include difficulty swallowing, vertigo, numbness of the face or body, nausea, and double or blurred vision. These are the very symptoms that lead clinicians astray, because each one individually is far more often caused by something benign. Vertigo alone sends millions of people to emergency departments every year, and the vast majority have an inner-ear issue, not a stroke.

Why These Strokes Get Missed

Posterior circulation strokes, including those from vertebral artery occlusion, are misdiagnosed at roughly twice the rate of strokes affecting the front of the brain. One study found that about 37% of posterior strokes were initially missed in the emergency department, compared with 16% of anterior strokes.¹⁴ The symptoms most strongly associated with a missed diagnosis were nausea and vomiting, dizziness, and a prior history of stroke. These findings are troubling because nausea and dizziness are cardinal features of posterior circulation events.

Part of the problem is that standard stroke screening tools like the FAST test (face drooping, arm weakness, speech difficulty, time to call) are designed to catch the lopsided weakness and slurred speech typical of anterior strokes. Misdiagnosed stroke patients were far more likely to screen negative on FAST, and they faced delayed imaging and worse discharge outcomes, including higher mortality.¹⁵ MRI can also be falsely negative in the first 24 to 48 hours for small brainstem infarcts, which adds another layer of missed opportunity.

A bedside eye examination called the HINTS test has emerged as a powerful tool for sorting out dangerous dizziness. It checks three things: the head impulse test (does the eye correct when the head is turned quickly?), nystagmus pattern (does it change direction with gaze?), and test of skew (is one eye higher than the other?). In one study, this three-step exam was 100% sensitive and 96% specific for identifying stroke among patients presenting with acute vertigo, outperforming early MRI.¹⁶ A systematic review confirmed the test’s usefulness in distinguishing posterior circulation stroke from benign causes of acute vertigo.¹⁷ The catch is that it requires training and practice, and many emergency physicians are not yet comfortable performing it.

Imaging the Vertebral Arteries

When vertebral artery occlusion or stenosis is suspected, several imaging methods are available. CT angiography is fast and widely accessible, making it the usual first choice in an emergency. Contrast-enhanced MR angiography tends to have higher sensitivity for detecting significant narrowing, while ultrasound (color duplex) is noninvasive and cheap but picks up fewer cases of stenosis. A systematic review found that contrast-enhanced MR angiography and CT angiography both had high sensitivity and specificity for detecting vertebral artery stenosis, while duplex ultrasound had excellent specificity but missed a larger share of stenoses.¹⁸ A head-to-head comparison confirmed that contrast-enhanced MR angiography had the best overall accuracy, CT angiography offered good specificity, and duplex ultrasound was the least sensitive of the three.¹⁹

In practice, the choice often depends on the clinical scenario. A patient rolling into the emergency department with sudden vertigo and imbalance will typically get a CT angiogram because speed matters. A patient being worked up for recurrent posterior circulation symptoms in an outpatient setting might get MR angiography for its superior sensitivity without radiation exposure. Catheter-based angiography, which threads a thin tube directly into the arteries, remains the gold standard for resolution but is reserved for situations where intervention is planned.

Acute Treatment With Clot-Dissolving Drugs

When a vertebral artery occlusion causes an acute ischemic stroke, intravenous thrombolysis with alteplase (a clot-dissolving drug) is the established first-line treatment if the patient arrives within the standard treatment window. Posterior circulation strokes actually appear to carry a lower risk of bleeding complications from thrombolysis than anterior strokes. A large registry study and meta-analysis found that the risk of symptomatic intracranial hemorrhage after thrombolysis was roughly half in posterior circulation stroke compared with anterior circulation stroke.²⁰ Favorable outcomes after thrombolysis for posterior circulation stroke have been reported in roughly 38 to 49% of patients.²¹

A recent trial pushed the treatment window further. In a study of Chinese patients with mainly mild posterior circulation stroke who did not receive thrombectomy, alteplase given 4.5 to 24 hours after stroke onset led to functional independence in about 90% of patients at 90 days, compared with roughly 73% receiving standard care alone.²² The rate of symptomatic brain bleeding remained low in both groups. This is encouraging for patients who arrive late, though the results apply specifically to the population studied and await broader replication.

Mechanical Thrombectomy

For large-vessel occlusions in the posterior circulation, mechanical thrombectomy, where a catheter is threaded into the blocked artery to physically extract the clot, is increasingly used. Thrombectomy has been well established for anterior circulation strokes, but evidence in the vertebrobasilar territory has accumulated more slowly. In one institutional series of 17 patients, recanalization (reopening of the artery) was achieved in about 71% of cases, with good functional outcomes at 90 days in about 59%.²³

Even more striking, a study examined outcomes of endovascular treatment in patients with vertebrobasilar occlusion presenting beyond 24 hours, well past the conventional treatment window. Successful reperfusion was achieved in over 80% of the treatment group, and the findings suggested improved functional outcomes, though the authors underscored the need for randomized trials to confirm the benefit.²⁴ The posterior circulation may tolerate longer treatment windows than the anterior circulation because the brainstem has a somewhat different metabolic profile and collateral supply, but this is an area of active investigation.

Stenting for Vertebral Artery Stenosis

You might assume that if a vertebral artery is severely narrowed, placing a stent to hold it open would prevent future strokes. The evidence tells a more nuanced story. The VAST trial, which randomized patients with symptomatic vertebral artery stenosis to stenting plus medical therapy or medical therapy alone, found that about one in 20 stented patients had a major vascular complication around the time of the procedure. Meanwhile, the rate of recurrent stroke under best medical treatment alone was low enough to question whether a larger trial was even feasible.²⁵

The VIST trial found a trend toward benefit with stenting but the difference was not statistically significant, with an absolute risk reduction of 25 strokes per 1,000 person-years that could have been due to chance.²⁶ A pooled analysis of individual patient data from multiple trials confirmed that stenting for vertebral stenosis did not show a clear benefit for stroke prevention and that the procedure was considerably riskier when the narrowing was inside the skull rather than at the artery’s origin.²⁷ For now, stenting remains reserved for carefully selected patients who have recurrent strokes despite aggressive medical therapy.

Long-Term Prevention After Vertebral Artery Occlusion

Once someone has had a stroke or transient ischemic attack from vertebral artery disease, the priority shifts to preventing the next event. The foundation is antiplatelet therapy. A single antiplatelet agent like aspirin reduces the relative risk of recurrent stroke by roughly 22%. For patients with minor stroke or high-risk transient ischemic attack, a short course of dual antiplatelet therapy with aspirin plus clopidogrel or ticagrelor for 21 to 30 days has proven more effective than a single agent when started early.²⁸ After the initial period, stepping down to a single antiplatelet is standard, because the bleeding risk of prolonged dual therapy starts to outweigh the benefit.

Beyond blood thinners, aggressive control of the usual vascular risk factors, blood pressure, cholesterol, blood sugar, and smoking cessation, is the other pillar of prevention. Statins, blood-pressure medications, and lifestyle changes do the heavy lifting. If the occlusion was caused by dissection rather than atherosclerosis, anticoagulation with a blood thinner like warfarin or a direct oral anticoagulant is sometimes used during the acute healing phase, though antiplatelet therapy is also considered acceptable in many cases.

Prognosis and What Shapes Recovery

Outcomes after vertebral artery occlusion vary enormously depending on the extent of the stroke, the underlying cause, and how quickly treatment begins. In a large cohort study of over 10,000 patients with vertebrobasilar disease, those with full occlusion had a significantly higher risk of death over one year compared with those who had stenosis short of occlusion.²⁹ The risk of recurrent stroke trended higher but was not statistically significant after adjusting for other risk factors, while the risk of death was more than double.

For people with vertebral artery origin stenosis who receive modern medical therapy, the annual rate of posterior circulation ischemic stroke is relatively low overall, though it is significantly higher in those whose stenosis was symptomatic compared to those discovered incidentally.³⁰ Long-term functional outcomes depend heavily on the neurological damage from the initial stroke. Patients who present early, with milder deficits, and receive prompt treatment tend to do well. In contrast, patients with large brainstem infarcts may face lasting disability affecting swallowing, balance, and coordination.

Bow Hunter Syndrome and Positional Occlusion

Bow hunter syndrome deserves a closer look because it represents a unique, treatable form of vertebral artery occlusion. Unlike atherosclerosis, which causes progressive narrowing, this condition involves mechanical compression of the artery during head rotation. A person might feel fine looking straight ahead but develop vertigo, visual disturbance, or even lose consciousness when turning to one side. The underlying cause is typically a bony abnormality at the C1-C2 junction that pinches the artery when the neck rotates.

Diagnosis requires dynamic imaging, meaning the scans must be performed with the head turned into the provocative position. Standard angiography with the head in a neutral position will miss it entirely. Treatment usually involves surgical stabilization of the cervical spine to prevent the compressive movement. In a series of patients treated with a strategy prioritizing spinal fusion surgery, none experienced recurrent symptoms after discharge, and long-term outcomes were excellent, with functional recovery largely determined by the degree of neurological damage before treatment.³¹ The rarity of the condition means that large randomized trials do not exist, but case series consistently show good results with surgery.

When Dizziness Warrants Urgent Evaluation

Not every episode of dizziness signals a vertebral artery problem. The overwhelming majority of vertigo is caused by benign inner-ear conditions. But certain patterns should prompt urgent evaluation. New-onset vertigo accompanied by difficulty walking, double vision, slurred speech, trouble swallowing, severe headache, numbness on one side of the face or body, or Horner syndrome (a droopy eyelid with a small pupil) warrants an immediate trip to the emergency department. The combination of vertigo with any neurological symptom shifts the probability from inner ear to brainstem, and time-sensitive treatments like thrombolysis and thrombectomy are available.

If you have known vascular risk factors and experience recurrent brief episodes of dizziness, imbalance, or visual dimming, especially if triggered by head turning, that pattern may suggest intermittent vertebrobasilar insufficiency and deserves workup even if each episode resolves on its own. The point is not to alarm everyone with occasional lightheadedness but to encourage a lower threshold for evaluation when the symptom profile, risk factors, and timing line up with a posterior circulation event.