Vertebral Artery Dissection

Etiology

Patients typically report minor, rather innocuous precipitating events before the onset of symptoms. Coughing, vomiting, chiropractic procedures, and blunt trauma are likely initiating events. It is estimated that 1 in 20,000 cervical spine manipulations cause a stroke. [4][5][6]Blunt trauma to the neck is the most common reported precipitating event. Patients with connective tissue disorders are also at increased risk. Ehlers-Danlos syndrome is the most common connective tissue disorder that can cause vertebral artery dissection. When patients with serious cervical cord injury or spine fractures are screened for vertebral artery injury approximately 20 to 40% will demonstrate traumatic occlusion. Interestingly, this occlusion tends to be asymptomatic, as opposed to dissection, and its management is controversial.

Other risk factors for vertebral artery dissection include:

• Yoga
• Nose blowing
• Painting the ceiling
• Judo, wrestling
• Hypertension
• Fibromuscular dysplasia
• Female gender
• Use of the birth control pill
• Cystic medial necrosis
• Vasculitis
• Postpartum[7]

Epidemiology

It is estimated that vertebral artery dissection is the cause of approximately 2% of all ischemic strokes. However, in middle-aged and younger patients (30 to 45 years of age), it is believed to be as high as 10% to 25%, representing a significant population affected by this condition. The combined incidence of both vertebral artery and carotid artery dissections is estimated to be 2.6 per 100,000. Carotid artery dissections are three to five times more common than vertebral artery dissections. It should be noted that chiropractors dismiss the association between manipulation and vertebral artery dissection on the grounds that the dissection is the cause of neck pain and the reason why the patients seek out chiropractic care. There is no conclusive evidence linking the two leading some medical associations only to suggest a causative link.

Pathophysiology

Vertebral artery anatomy

1. Segment 1 takes off at the first branch of the subclavian artery until it reaches the foramina of C5-C6.
2. Segment 2 runs within the transverse foramina from C5/C6 until C2.
3. Segment 3 is the tortuous segment that starts at the transverse foramina of C2 and runs in the posterolateral part, looping around C1 and then passing between the atlas and the occiput. This segment of the artery is encased with nerves, muscles, and the atlanto-occipital membrane.
4. Segment 4 is the intracranial segment; it pierces the dura at the foramen magnum runs until the junction of the medulla and pons; here it merges with the basilar artery.

The majority of spontaneous dissections occur in segment 3, which may extend and involve segment 4.

The arterial anatomy consists of three layers named the intimal (innermost), the media (middle), and the adventitia (outermost layer). Dissection occurs when the structural integrity of the arterial wall is compromised. Intimal tears lead to arterial blood dissecting between the layers of the arterial wall. The blood within the arterial wall precipitates hematoma and clot formation.[8] The subsequent compromise in arterial blood flow secondary to the stenosis then leads to the symptoms of vertebral artery dissection and ultimately, stroke. Vertebral artery dissection can be either extracranial or intracranial.  Extracranial dissections usually involve the distal extracranial segment near the atlas and axis. Intracranial dissections are often associated with subarachnoid hemorrhage and carry a much worse prognosis. Neurological sequelae of both extracranial and intracranial dissections may result from cerebral ischemia due to thromboembolism, hypoperfusion, or a combination of both. However, thromboembolism rather than hypoperfusion is considered the major cause of ischemic symptoms.

History and Physical

History

Clinical presentation is typically acute and severe unilateral neck pain and/or a headache. Minor neck trauma often precipitates the pain. The pain is typically in the occipital-cervical area of the neck or head. Often the trauma is minor in nature.

Neurological symptoms are often delayed and may not be present at all. However, 70% of patients will have some type of neurological deficit which may present late

Lateral medullary syndromes (Wallenberg Syndrome) and cerebellar infarctions are the most common location for strokes. Wallenberg Syndrome is defined by sensory deficits affecting the trunk and extremities on the opposite side of the infarction and sensory deficits affecting the face and cranial nerves on the same side as the infarction. When neurological symptoms are present, dizziness, ataxia, dysphagia (cranial nerves 9 and 10), disequilibrium, unilateral hearing loss, dysarthria, diplopia, and vertigo are the predominant symptoms.

Extracranial dissections often have a bruit present. The bruit has even been reported on the contralateral side secondary to increased collateral blood flow. What often distinguishes this type of patient from those with cerebellar infarctions secondary to atherosclerotic disease is the age of the patient and the presence of pain. When the dissection is intracranial, a subarachnoid hemorrhage is present 50% of the time. This group of patients has severe neurological symptoms a much worse prognosis than those with extracranial dissections.

Physical Exam

• Nystagmus
• Truncal ataxia
• Ipsilateral loss of taste (hypogeusia), horner syndrome, impairment of proprioception and fine touch
• Contralateral impairment in thermal and pain sensation in the extremities
• Tongue deviation to the side of the lesion
• Internuclear ophthalmoplegia

Evaluation

MRI rivals angiography for establishing the diagnosis but is not readily available to most. CT and CTA are often the first investigations obtained. CT scan can demonstrate posterior fossa ischemia or subarachnoid hemorrhage. It may also identify an occluded vertebral artery or mural thrombus. CTA, however, is superior to CT scan and should be performed. CTA more easily identifies irregularity of the vascular lumen or thickening of the arterial wall. CTA is the initial test of choice. Vascular Duplex scanning demonstrates abnormal flow in 95% of patients. However, it shows evidence specific to dissection in only 20% of patients.[9]

MRI may detect an intimal flap and luminal thrombosis. Sometimes hyperintensity of the vessel wall may be visualized on T1 weighted images and are considered pathognomonic.

A cerebral angiogram may be required if the MRI and CT scan have failed to reveal any pathology

Routine blood work including coagulation profile should be obtained.

If CT reveals the absence of hemorrhage, then anticoagulation can be initiated.

Treatment / Management

For those patients that survive the initial dissection, the prognosis is usually good. Approximately 10% of patients die initially.

The goal of management is to prevent stroke, which is the complication of vertebral artery dissection. Management is done with anticoagulation, typically heparin. If there are no contraindications, then thrombolytic therapy can be started as long as the time is within 4.5 hours from the onset of symptoms.

In one clinical follow-up study, 80% achieved a full recovery. Death is typically secondary to extensive intracranial dissection, brainstem infarction, or subarachnoid hemorrhage. Most dissections will resolve over time with no neurological deficits. Be advised however that when the dissection is intracranial or extends intracranially, the risk of subarachnoid hemorrhage increases significantly and anticoagulation is contraindicated. [10][11][12]Endovascular or surgical treatments are reserved for patients with concomitant complications or those whose maximal medical therapy has been unsuccessful.

Admission is required for all patients with vertebral artery dissection. Close monitoring of neurological deficits is vital.

Today technological advances have permitted the use of endovascular therapies to manage vertebral artery dissection. However, the role of this therapy does remain controversial as most patients can be managed with anticoagulation therapy. In addition, most dissections do a repair on their own. Thus, endovascular therapy is best reserved for patients who are not candidates for thrombolytics and/or have a subarachnoid hemorrhage.

Surgery in the form of bypass graft is rarely done and not always successful.

Secondary prevention strategies include reducing risk by targeting and modifying vascular risk factors. Aspirin is used as preventative therapy is aspirin for most etiologies. For atrial fibrillation, anticoagulation is recommended. Most stroke patients, including young adults, should be treated with statin therapy.[13]

Differential Diagnosis

• Cervical spine fracture evaluation

• Cervical strain

• Emergent management of subarachnoid hemorrhage

• Migraine headache

• Stroke, hemorrhage

• Stroke, ischemia

• Tension headache

• Vasculitis affecting the vertebrobasilar circulation

• Vertebrobasilar atherothrombotic disease

Prognosis

For patients who do survive the initial acute extracranial dissection, the prognosis is good with complete recovery in nearly 80-90% of patients. However, at least 10% will develop recurrent attacks, a major stroke, or death. Patients who have severe neurological deficits at the time of presentation usually do have a poor prognosis. Follow-up angiographic studies have revealed healing in about 60% of patients.

Patients who develop an intracranial dissection have a poor prognosis. Those who present with altered consciousness and neurological deficits do poorly. Intracranial vertebral dissections are often associated with brainstem infarctions, subarachnoid hemorrhage, and death.

Prognosis may be very different for young patients without comorbidities like hypertension, diabetes, and smoking compared to those who have them.

Complications

• Cerebellar and brain stem infarction
• Subarachnoid hemorrhage
• Vertebral artery pseudoaneurysm leading to compression neuropathy of the cranial nerves.