Vertebrobasilar Stroke

Etiology

Stroke is seen as an "end-stage disease" of multiple chronic and uncontrolled comorbidities. The risk factors of vertebral artery or basal artery stroke are no different from other types of strokes. Hypertension, diabetes mellitus, cigarette smoking, obesity, atrial fibrillation, sedentary lifestyle, hyperlipidemia, illicit drug use such as cocaine, or hypercoagulable states increase the risk of experiencing a stroke. The most common risk factor is hypertension being comorbid in about 70% of patients; however, the likelihood of having as troke increases with multiple comorbidities. Strokes can be divided into ischemic and hemorrhagic, while ischemic strokes can be further delineated into thrombotic, embolic, and lacunar subtypes.[1]

Lacunar strokes are caused by uncontrolled hypertension, which causes decreased perfusion in small vessels located most commonly in the internal capsule, thalamus, or less frequently, the brainstem. Thrombotic strokes are caused by excessive atherosclerotic plaque buildup on the arterial wall, which eventually completely occluded the vessel. Embolic stroke results from a blood clot or a broken off atherosclerotic plaque, which transverses from one area of the cardiovascular system, eventually occluding a part of the cerebrovascular system. Hemorrhagic strokes are commonly caused by aneurysm ruptures, uncontrolled hypertension, arteriovenous malformations, metastasis, amyloid angiopathy.[2][3]

Epidemiology

While the mortality and prevalence of stroke have decreased over the past thirty years, from 40% to 33% in 2013, outcomes vary between populations stratified among race, geography, and comorbidities. Stroke is currently the third leading cause of mortality in the United States. Individuals who live in the "stroke belt," which predominately involves the Southeast United States, have a 20% higher mortality than those living outside this geographic area. Women have a higher lifetime risk and mortality than men, although stroke is more common in men. The incidence of stroke is more common in minority populations, specifically Hispanic and Black populations, with mortality occurring in younger individuals on average compared to the White population. An increased lifetime incidence of stroke is seen in those with more comorbidities listed under the etiology section above, with recurrent stroke most common in individuals with multiple uncontrolled risk factors. Posterior circulation strokes have been reported to account for as much as 20% of all strokes.[4][5]

Pathophysiology

Strokes are brain tissue that has suffered prolonged ischemia from the failure of the sodium-potassium pump in nerve cells to utilize ATP due to an inability to undergo aerobic metabolism. Prolonged ischemia causes lactic acidosis and accumulation of calcium, sodium, and potassium in cells, which causes dysfunction of protein synthesis as well as swelling and eventual disruption of the plasma membrane. The result is the release of cytotoxic free radicals that promote surrounding cell death. In vertebrobasilar strokes, ischemia is most often a result of a thrombus causing severe or complete occlusion of the cerebrovasculature; however, specific syndromes may involve other listed etiologies below.[6]

History and Physical

A stroke of the vertebral or basilar artery should be suspicious in a patient presenting with vestibulocerebellar symptoms, including dizziness, nystagmus, truncal and/or limb ataxia, hypotonia of one side, oscillopsia, or cranial nerve impairment. 

Intracranial Vertebral Arterial Strokes

Lateral medullary infarction (Wallenberg syndrome)

The most common posterior circulation stroke, which is generally the result of atherothrombotic occlusion of the vertebral artery causing ischemia to the lateral part of the medulla. This ischemia impairs the inferior vestibular nucleus, solitary, and ambiguous nuclei, causing the classic presentation of hoarseness, dysphagia, ataxia, and vertigo. The patient can also experience crossed hemianesthesia, indicating a brainstem lesion, with ipsilateral facial sensory loss and contralateral upper and lower extremity anesthesia due to dysfunction of the spinothalamic tract and descending trigeminal tract. This syndrome does not affect muscle strength as the corticospinal tract is located ventrally in the brainstem.[7][8] 

Medial Medullary Infarction (Dejerine syndrome)

Medial medullary infarction is also known as inferior alternating syndrome. It is a result of ischemia to the medial medulla due to occlusion of paramedian branches of the vertebral artery. The classic presentation is ipsilateral tongue paralysis, contralateral limb weakness, contralateral limb anesthesia resulting from impairment to the hypoglossal nerve, dorsal medial lemnisci, and corticospinal pathways. The crossed paralysis localizes the lesion to the brainstem due to ischemia from undecussated corticobulbar fibers located in the medulla.[9][10][11]

Hemimedullary Infarction

This is a rare stroke that involves ischemia to the medial and lateral medullary due to intracranial vertebral artery occlusion proximal to the anterior spinal artery, which results in a combination of symptoms of both lateral and medial medullary syndromes.[12][13]

Cerebellar Infarction (Pseudotumoral Cerebellar Syndrome)

The presenting symptoms depend on the artery that is obstructed. Interruption of the posterior inferior cerebellar artery results in vertigo, truncal ataxia, horizontal nystagmus. The anterior inferior cerebellar artery (AICA) causes dysmetria, loss of hearing on the ipsilateral side, paralysis of the ipsilateral face. Occlusion of the superior cerebellar artery, which receives supply from the basilar artery later discussed in this article, causes dysarthria, ataxia, and vomiting. Space in the posterior fossa is limited, and large cerebellar strokes may cause herniation discussed further in the complications section.[14][15]

Basilar Artery Strokes

Top of the Basilar Syndrome

This is also known as a rostral brainstem infarction is caused by embolic occlusion of the distal basilar artery causing ischemia to the midbrain, temporal, and occipital lobes producing vertical gaze palsy, pupillary palsy, hypersomnolence, abulia, amnesia, and visual hallucinations. Notably, sensory and motor dysfunction is generally not present.[16][17]

Inferior Medial Pontine Syndrome (Foville Syndrome)

Inferior medial pontine syndrome or isolated dorsal pontine tegmentum infarcts is also termed Foville’s syndrome. It results from occlusion of perforating pontine arteries, commonly due to atherosclerosis of the basilar artery. This syndrome results in ipsilateral cranial nerve VI, VII, and contralateral limb hemiparesis and hemianesthesia.[18] 

Ventral Caudal Pontine Infarct (Millard-Gubler Syndrome)

This syndrome most often arises due to mass effect compression of one side of the caudal pons due to tumors, hemorrhage, and infections. It has been observed in younger patients can be caused by demyelinating diseases or viral encephalitis. This compression causes ipsilateral facial and lateral rectus palsy, with contralateral limb hemiplegia. These symptoms are due to dysfunction of the abducens and facial nerves and interruption of the corticospinal tract.[19][20]

Ventral Medial Pontine Infarct (Raymond Syndrome)

This is a very rare pontine stroke with two subtypes: classic Raymond syndrome and common Raymond syndrome. The classic subtype presents as ipsilateral lateral rectus with contralateral facial nerve paralysis and limb hemiparesis secondary to medial midpontine infarct. The common subtype spares the face and is secondary to an infarct that does not include corticofacial fibers.[21][22]

Raymond–Cestan Syndrome

This syndrome is caused due to the lesion involving the upper dorsal pons. It manifests as ipsilateral ataxia and coarse intention tremor, ipsilateral paralysis of muscles of mastication and sensory loss in the face, contralateral sensory loss in the body, and contralateral hemiparesis of the face and the body. [23]

Gasperini Syndrome

This is a rare syndrome caused by impairment of the caudal pons tegmentum, which presents with ipsilateral CN V, VI, VII, and VIII impairment with contralateral limb hemianesthesia. This syndrome has been observed in demyelinating conditions like multiple sclerosis and ischemic events due to occlusion branches of the basilar and AICA arteries.[24][25]

Lateral Pontine Syndrome (Marie Foix Syndrome)

This is a rare brainstem stroke caused by occlusion of the long circumferential branches of the basilar artery or the anterior inferior cerebellar artery. This syndrome presents with ipsilateral peripheral facial nerve deficits with loss of facial pain and temperature, ipsilateral hypacusis, ipsilateral Horner syndrome, contralateral extremity hemiparesis, and pain and temperature sensory loss and extremity ataxia.[26] 

Weber Syndrome (Superior Alternating Hemiplegia) 

This presents from occlusion of paramedian branches of the posterior cerebral artery (PCA) or the basilar bifurcation perforating arteries in the midbrain. It presents with ipsilateral CN III palsy and contralateral hemiparesis of extremities and face. This syndrome can also present with vertical gaze paralysis if the ischemic region includes the red nucleus.[27]

Paramedian Midbrain Syndrome (Benedikt Syndrome)

Occlusion of the paramedian penetration branches of the basilar artery causes ipsilateral CN III palsy with contralateral loss of proprioception and vibration, and ataxia. It is separated from Weber syndrome in that this syndrome has a tremor and choreoathetotic movements, whereas Weber has hemiparesis.[28][29]

Evaluation

First responders perform prehospital stroke assessments to identify potential stroke patients quickly. There are many assessments; however, the most common one is the Cincinnati Prehospital Stroke Assessment, which assesses facial droop, arm drift, and speech. A last known well time should be obtained, which documents the last time a patient was observed at their baseline health to better triage eligible patients to transfer patients to primary or comprehensive stroke centers. At these centers, a neurologist performs a rapid initial assessment using the National Institute of Health’s Stroke Scale to localize strokes and document an initial standardized exam to monitor progression. This scale ranges from 0 to 42 and includes categories that assess the level of consciousness, best gaze, visual field, facial palsy, motor function in each limb, limb ataxia, sensation, language, dysarthria, extinction, and neglect.

A non-contrast CT of the head or brain MRI should be performed within 20 minutes of initial presentation to evaluate for intracranial hemorrhage. Vessel angiography using either a CT or MR scanner is obtained of the head and neck to evaluate for potential large vessel occlusion, which could be manually removed through a procedure known as thrombectomy to revascularize tissue at risk of ischemia. Hospitals without this imaging modality are recommended to call a teleradiology service to contact a stroke neurologist for advice on administering thrombolytics and further workup.

Blood glucose should be tested to rule out hypoglycemia as a cause of neurological deficits. Other workups will include a complete blood count and metabolic panel, troponin, and coagulation factors. An echocardiogram should be performed to rule out simultaneous cardiac disease.[30][31]

Treatment / Management

Treatment of strokes requires an interprofessional specialized team found at centers that specialize in stroke care. Team members include neurology, neurosurgery, neuro-intensivists, specialized nursing, rehabilitation medicine with physical, occupational, and speech therapists.

Ischemic Strokes

Treatment of ischemic strokes is time-dependent. If the onset of symptoms occurs before 4.5 hours without evidence of hemorrhage on a non-contrast CT scan, the patient is tissue plasminogen activator (TPA) eligible, the preferable agent being IV alteplase. The dose of alteplase is calculated as 0.9 mg/kg with a maximum dose of 90 mg. 10% of the total dose is given as a bolus over one minute, and the remainder is given over the next hour.  There is a set of inclusion criteria and contraindications that should be discussed with the patient to obtain informed consent before administering the medication. This is generally performed by a neurologist specializing in stroke; however, another physician can perform it with guidance. Most notable contraindications include recent intracranial surgery or trauma, active internal bleeding, intracranial hemorrhage, blood pressure greater than 180/90 mmHg. Inclusion criteria are stroke with a measurable neurological deficit occurring less than 4.5 hours. There are relative exclusion criteria for patients greater than 80 years old, NIHSS score greater than 25, and current anticoagulant use.[32]

While posterior circulation strokes were not included in the DAWN or DEFUSE-3 trials, recent studies have shown thrombectomy can be performed on posterior circulation ischemic strokes. These studies have also noted to have a lower rate of hemorrhage when compared to anterior circulation strokes. In this procedure, a puncture through the femoral artery at the groin is made to insert a clot retriever device to remove a thrombus obstructing a large intracranial vessel manually. Using fluoroscopic guidance, the degree of vessel recanalization is categorized as Thrombolysis In Cerebral Infarction (TICI) score is assigned 0 to 3, with TICI 3 representing complete perfusion.[33]

After treatment with TPA and/or thrombectomy, the patient is later observed in a neuro focused ICU setting for close monitoring of vitals. Blood pressure is permissively elevated to 180/90 mmHg to allow tissue reperfusion in the first 24 hours after the intervention. If no therapy is given, blood pressure is more permissive to 220/110 mmHg. Strict blood pressure can be controlled using IV antihypertensives such as nicardipine, clevidipine, hydralazine, or labetalol. Hourly neuro checks are also performed to assess for a change in their neurological exam to indicate an acute complication such as intracranial hemorrhage, edema with midline shift or herniation, or a repeat ischemic stroke. If a change is documented, a stat CT of the head without contrast should be obtained.

Hemorrhagic Strokes

This life-threatening condition requires an immediate neurosurgical assessment, depending on the extent of bleeding, and acute surgical intervention may be necessary depending on the site of hemorrhage. A head CTA should be performed to localize the hemorrhaged vessel to evaluate for surgical intervention. These cases should also be observed in a Neuro ICU setting. Hemorrhage into the ventricular space can obstruct CSF flow and may require placement of an extra ventricular drain through the scalp to manually drain CSF and reduce ventricular pressure. Hemorrhage into the parenchyma is generally monitored closely in the ICU for evaluation of midline shift. Blood pressure should be controlled using IV antihypertensives listed above to maintain pressure below 160/90 mmHg. Anticoagulant and pharmacological deep venous thrombosis (DVT) prophylaxis are recommended to be held in the acute management of this disease to prevent worsening intracranial bleeding.[32]

Differential Diagnosis

• Benign positional paroxysmal vertigo
• Brainstem migraine
• Dolichoectasia of the vertebral or basilar artery
• Intracranial tumor
• Labrythnthitis
• Postictal state with Todd paralysis
• Thyroid disease
• Transient ischemic attack
• Vertebrobasilar insufficiency
• Vestibular neuritis

Prognosis

The prognosis of vertebrobasilar strokes is dependent on the amount of brain ischemia and treatment provided. Prior baseline function, age, and ability to undergo physical therapy also drastically change expected outcomes.

Complications

Side effects of TPA include intracranial hemorrhage, nausea, angioedema of the tongue, which, if it develops, is promptly stabilized by holding TPA and ACE inhibitors, administering IV steroids, and intubation.[34]

A complication of large ischemic and hemorrhagic strokes is vasogenic or cytotoxic edema, causing increased intracranial pressure and mass effect, which shifts structures midline and downward, possibly compressing the brainstem, and in severe cases can herniate downwards through the foramen magnum. Before this occurs, patients can be given mannitol and/or hypertonic saline in hopes of preventing hemicraniectomy.[32]