Vertebrobasilar Insufficiency

Article Author:
Letitia Pirau
Article Editor:
Forshing Lui
Updated:
3/31/2019 11:16:39 PM
PubMed Link:
Vertebrobasilar Insufficiency

Introduction

Vertebrobasilar insufficiency (VBI) is defined by inadequate blood flow through the posterior circulation of the brain, supplied by the 2 vertebral arteries that merge to form the basilar artery. The term was coined in the 1950s after C. Miller Fisher used carotid insufficiency to describe transient ischemic attacks (TIA) in the carotid supplied territories and is therefore often used to describe brief episodes of transient ischemic attacks in the vertebrobasilar territory. Also known as the posterior circulation, the vertebrobasilar vasculature supplies areas such as the brainstem, thalamus, hippocampus, cerebellum, occipital and medial temporal lobes. Although patients may initially be asymptomatic, the significant build-up of atherosclerotic plaques over time may lead to ischemic events. Stroke may occur either due to an occlusion of the vertebral or basilar artery or an embolus that that may lodge more proximal to the brain[1]. In the emergency setting, VBI is an important diagnosis to consider as many symptoms can appear like other benign etiologies such as labyrinthitis, vestibular neuritis, and benign paroxysmal positional vertigo (BPPV).

Etiology

Certain risk factors predispose patients to VBI, particularly those that exacerbate atherosclerosis. These risk factors include smoking, hypertension, age, gender, family history and genetics, and hyperlipidemia. Furthermore, patients with a history of coronary artery disease or peripheral artery disease are at increased risk [2]. The other etiological causes may include cardioembolic conditions such as atrial fibrillation, infective endocarditis, vertebral artery dissection, and systemic hypercoagulable states.

Epidemiology

About a quarter of strokes and TIAs occur in the vertebrobasilar distribution. Like the prevalence of atherosclerotic disease, vertebrobasilar disease occurs later in life, particularly around the 7 to 8 decades, with a predilection for the male gender. As many as 25% of the elderly population present with impaired balance and increased fall risks as a consequence of VBI. Similar to other types of stroke syndromes, African Americans are more prevalent than other ethnic groups due to multiple reasons including genetics, higher prevalence of hypertension and differences in healthcare delivery.

Pathophysiology

As with other types of strokes, infarct can occur from either an embolism, in-situ thrombosis, or lacunar disease secondary to chronic hypertension. Usually, VBI is caused by 2 processes of ischemia: hemodynamic insufficiency and embolism.

Hemodynamic

Decreased perfusion causes most VBI. Hemodynamic ischemia occurs to inadequate blood flow through the basilar artery, especially in the elderly and diabetic populations with poor sympathetic control. Symptoms tend to be reproducible and short, rarely causing infarction. For hemodynamic ischemia to occur, there must be occlusion in both vertebral arteries or within the basilar artery. Also, there must be an incomplete contribution by the carotid circulation via the posterior communicating artery in the circle of Willis. Other causes for a decrease in perfusion include antihypertensive medications, cardiac arrhythmia, pacemaker malfunction, and vasculitis. Thus, it is imperative that a complete workup, including ECG, be done to rule out cardiogenic causes. Occlusions in other blood vessels such as in Subclavian Steal syndrome may also cause VBI by “stealing” blood flow from the brainstem as blood flows down the path of least resistance via the vertebral artery in the presence of proximal stenosis/occlusion of the subclavian artery.

Embolism

VBI may also originate from atherosclerotic plaques that later break off to form emboli. However, emboli may also develop as a result of intimal defects secondary to trauma, compression, and in a minority of cases from fibromuscular dysplasia, aneurysm or dissection. Possibly up to one-third of cases occur intracranially, as distal emboli form from lesions within the subclavian, vertebral, or basilar artery. Most lesions that form extracranially arise from an atherosclerotic buildup in one of the vertebral arteries, and rarely the innominate or subclavian. In a very small number of cases, thrombi can arise from an ectatic or fusiform basilar artery aneurysm which may then embolize to more distal branches[3][4][5].

History and Physical

The most common findings in a patient’s history to suggest VBI include risk factors for cardiovascular diseases such as atherosclerosis and advanced age. A thorough history and physical exam should be completed, with special attention to not only the neurological but cardiac exam for conditions such as an arrhythmia which may cause the symptoms as well. Symptoms of VBI are a result of ischemia on the different parts of the brain supplied by the posterior circulation.

Symptoms include:

  • Vertigo (the most common symptom)
  • Dizziness/syncope: Sixty percent of patients with VBI have at least 1 episode of dizziness. 
  • "Drop attacks:" Patient feels suddenly weak in the knees and fall
  • Diplopia/Loss of vision
  • Paresthesia
  • Confusion
  • Dysphagia/dysarthria

 If VBI advances into a brainstem infarction, several syndromes may arise depending on the location such as lateral medullary syndrome, medial medullary syndrome, basilar artery syndrome, and Labyrinthine artery occlusion. Other aspects of the history which should be noted during the physical exam are reproducible symptoms during positional head changes, i.e., syncope while turning the head laterally (Bow Hunter syndrome) or during head extension [6][7][8].

Care must be taken to rule out other more benign conditions that may also cause similar symptoms such as labyrinthitis, vestibular neuritis, and benign paroxysmal positional vertigo (BPPV). Vertigo is a common symptom in VBI. It is also a central symptom of peripheral vestibular disorders which are more benign. It is especially important in the emergency department setting to differentiate between vertigo due to peripheral vestibular disorders and central vestibular problems most commonly due to vertebrobasilar insufficiency (VBI) which may require hospitalization. Vertigo by itself cannot be diagnosed as TIA or VBI. Vertigo in the presence of brainstem signs or symptoms will be diagnostic of vertebrobasilar territory TIA. Physical examination to look for brainstem signs or cranial nerve abnormalities is very important. Presence of contralateral extremity signs or symptoms is helpful. The type of nystagmus such as vertical nystagmus or direction changing nystagmus is indicative of VBI. The head thrust test if performed and interpreted properly may differentiate peripheral vertigo from central vertigo due to VBI at the bedside. A positive head thrust test is indicative of a peripheral cause of vertigo.

Evaluation

Imaging of the vertebral and basilar arteries via arteriography is important for the diagnosis and management. Noninvasive CTA or MRA is commonly used to visualize the vertebral-basilar system to define stenosis or occlusions. CTA will produce good images both intracranial and extracranial vessels [9]. The extracranial vessel may require contrast-enhanced MRA due to swallowing artifacts. For CTA caution must be taken into consideration given the nephrotoxicity of the contrast and radiation exposure. In the presence of an impaired renal function, gadolinium MR contrast may also result in the rare complication of nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy (NFD). MRI is always a better imaging modality for brainstem and posterior fossa problems especially acute brainstem infarction with diffusion-weighted imaging. Other pathology such as brainstem cavernoma or cerebellopontine angle lesions including acoustic schwannoma and dermoid/epidermoid cysts, which may be identified by MRI convincingly.  Duplex ultrasound may also be used for abnormalities within the vertebral artery, albeit its limitations. Although difficult to visualize V1 and V2, duplex ultrasound may detect changes in flow velocity from proximal vertebral stenosis or subclavian steal. For patients who are older than the age of 45, work up should include identifying risk factors that may cause VBI such as cholesterol levels, lipids, blood sugar, blood pressure, and smoking cessation. If a patient is younger than 45 years old, further workup is indicated to rule out the cardioembolic cause, hypercoagulable states, vertebral dissection and fibromuscular dysplasia.

Treatment / Management

As with ischemic strokes in the anterior circulation, treatment of vertebrobasilar disease requires prompt management. Previous transient episodes (TIAs) can signal the onset of an infarct in the future. If the cause of embolism is determined to be cardiogenic, most likely due to atrial fibrillation or mechanical heart valves, then anticoagulation therapy is indicated. Although not as common, vertebral dissection secondary to trauma may also be the source of embolism, managed again with antithrombotic. Otherwise, treatment depends on reducing risk factors such as smoking, cholesterol, and hypertension. In the acute setting, the symptoms are often pressure/perfusion dependent. Perfusion may need to be augmented by IV fluid and attempt to avoid lowering the blood pressure. In the longer term, stricter blood pressure control is important in secondary stroke prevention. Similar to all types of ischemic events, secondary prevention will require a multimodality approach including BP control, quitting smoking, strict blood sugar control, use of a statin, lifestyle changes including diet and exercises [10]. Surgical options are very limited [11]. It depends on the location of the plaque and the efficacy of repair. The more distal the occlusion from the brain the more likely to consider surgery as an option [12]. The criteria for surgery depends on:

  • Bilaterally significant VA stenosis, i.e., greater than 60% stenosis IN BOTH arteries. Or greater than 60% stenosis in the dominant vertebral artery (VA) if contralateral is hypoplastic, ends in the posterior inferior cerebellar artery (PICA), or is occluded.
  • Symptomatic embolism believed to originate from a vertebral lesion
  • Symptomatic repair of an aneurysm or if an aneurysm is greater than 1.5 cm regardless of symptoms.

There are 2 options for surgical repair: open surgical repair and endovascular treatment. Open surgical repair involves a bypass graft over the stenosed area. Direct arterial transposition places the artery to a nearby healthy vessel and joining the 2 parts [13]. The most common procedure is endovascular repair, which involves placing a stent via a catheter in the groin. A balloon is then placed within the stenotic vertebral artery with eventual stent placement [14].

Enhancing Healthcare Team Outcomes

Vertebrobasilar insufficiency is managed by an interprofessional team that includes the emergency department physician, neurologist, radiologist, internist, and a stroke specialist. While the definitive treatment is under the care of a neurologist, the primary care provider and nurse practitioner should educate the patients on preventing further episodes. The patient should be discouraged from smoking, remain compliant with medications, maintain a healthy weight, ensure that the cholesterol levels are under control and participate in regular exercise. The outcomes for patients with vertebrobasilar insufficiency depends on the severity of the stroke, age, comorbidity, and degree of neurological deficit.


References

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