Vertebrobasilar disease describes a broad spectrum of vascular abnormalities in the arterial supply to the brain stem.
Description
The vertebrobasilar circulation (VC, also called the posterior circulation) consists of the arterial supply to the brain stem, cerebellum, and occipital cortex. The vertebral arteries arise from the subclavian arteries in the neck. In the brain, the vertebral arteries lie deep in the base of the brain and unite in an area called the medullopontine junction to form the basilar artery. The basilar artery branches again to form the posterior cerebral arteries. Any interruption in blood flow in the VC may cause a broad spectrum of symptoms determined by the specific arterial branch or branches involved, and the degree of occlusion inside the blood vessels. The brain stem is a major area of neurologic activity since this area contains cranial nerves, neurosensory tracts, and the reticular activating system (RAS). Problems in blood flow to the VC result in several overlapping clinical syndromes.
Demographics
In the United States, approximately 25% of strokes and TIAs (transient ischemic attacks or "mini" strokes) occur in the vertebrobasilar circulation. Research with magnetic resonance imaging (MRI) studies estimates that 40% of patients with vertebrobasilar TIAs (transient ischemic attacks) have brain stem infarction. The disease affects men twice as often as women. Vertebrobasilar ischemic disease occurs in late life, usually between 70–80 years of age. The incidence (number of new cases) is 20–30 cases per 1,000 for persons over age 75. In the United States, the death rate for stroke is higher among blacks than whites. A severe form of the disorder, called basilar artery syndrome, caused by complete obstruction of the vertebrobasilar circulation (inside the brain) is fatal in 75–85% of cases. Approximately 50% of persons who have infarctions in the vertebrobasilar area report TIA events within days or months prior to onset of permanent deficit.
Causes and symptoms
The cause of vertebrobasilar disease (VD) is atherosclerosis that affects the vertebrobasilar (posterior) circulation at intracranial (inside the cranium and includes the basilar artery) sites and extracranial (outside the cranium and includes the vertebral artery) sites. Partial or complete occlusion can occur in major arteries or smaller arterial branches. The cause of VD is atherosclerosis and vertebrobasilar insufficiency in the brain caused by blockage (occlusion), and is more common among patients with cardiovascular risk factors that typically include obesity, smoking, use of oral contraceptives, advanced age, diabetes mellitus, hypertension (high blood pressure). and dyslipidemias (abnormalities that cause an increase in lipids in the blood). Other causes of vertebrobasilar disease can include destruction to arteries such as fibrotic changes in the muscular layer of arteries (a condition called fibromuscular dysplasia) and arterial dissection or aneurysms.
The symptoms of TIA have a short duration and usually last approximately eight minutes. Vertigo is the hallmark symptom of vertebrobasilar insufficiency. Other symptoms include visual defects (diplopia), syncope (drop attacks), dysphagia (difficulty swallowing), dysarthria, hoarseness, and facial numbness, or paresthesias. Patients with early stage vertebrobasilar insufficiency have transient episodes of neurologic symptoms. Persons with more advanced disease to the vertebrobasilar circulation may have eye deficits, limb ataxia, loss of taste, limb/trunk dysesthesia, nystagmus, and deficit in temperature/pain perception.
Diagnosis
Neuroimaging studies are the primary diagnostic tool necessary to confirm vertebrobasilar disease. Other tests are also indicated and include analysis of blood, electrolytes, glucose, urinalysis, thyroid function tests, and erythrocyte sedimentation rate (a special blood test that rules out other possible disorders). Computed tomography (CT) scans help to detect mass defects and MRIs can help visualize smaller areas of ischemia. Ultrasound studies can help assess and monitor vertebrobasilar patency (the degree of occlusion).
Treatment team
A neurologist is typically required as the specialist coordinator of treatment. A neurosurgeon is used for surgical evacuation of hemorrhages complicated by hydrocephalus. An interventional neuroradiologist may be required to provide thrombolytic agents (chemicals that dissolve clots) by intra-arterial infusion delivery (injecting a chemical directly in an artery located in the brain using TV monitor-guided imagery).
Treatment
Treatment can be either supportive or interventional if arterial patency is an option. Emergency treatment for a bleeding patient includes airway preservation, control of blood pressure, and assessment of neurologic and mental status, intravenous fluid management, prevention of vomiting, and antiplatelet agents to prevent arterial occlusion. Additionally, a stroke patient may require treatment for hypertension if present, and mouth feedings should be avoided since the patient may be unable to swallow or chew. Antiplatelet medication is the first line treatment for vertebrobasilar disease, however, the usefulness is unclear. Anticoagulants (heparin) and antiplatelets (aspirin and ticlopidine) are typically given to prevent recurrent or ongoing occlusion (caused by blood clots) of the posterior (vertebrobasilar) circulation.
Recovery and rehabilitation
Recovery is variable depending on the degree of occlusion in the vertebrobasilar circulation. Persons with the severe form, basilar artery occlusion, often die in 75–85% of cases. Rehabilitation depends on the extent of damage and the deficits caused by permanent injury in the brain.
Clinical trials
Research in this area is diversified and abundant. Currently, the National Institute of Neurological Disorders and Stroke (NINDS) is investigating molecular mechanisms associated with neuronal injury. Research concerning the genetics of stroke and gene therapy is ongoing in experimental models. New research in high resolution neuroimaging techniques, and rehabilitation have demonstrated compensatory mechanisms (re-circuitry of neurons) as a result of stroke. Further information can be found at <http://www.clinicaltrials.gov>. or <http://www.ninds.nih.gov>.
Prognosis
Vertebrobasilar TIAs have a favorable outcome since the chance for complete stroke is minimal. Collateral circulation from smaller blood vessels may help to improve the outcome.
Special concerns
Clinicians must be vigilant to be suspicious of vertebrobasilar insufficiency in elderly patients who suffer from vertigo. Hemorrhage has to be ruled out before blood thinner (anticoagulation) treatment is initiated. Additionally, it is important to take special precautions when feeding persons with brain stem infarction, because patients can develop problems with normal swallowing mechanisms that can cause aspiration pneumonia (caused by food lodged in the lungs).
BOOKS
Goldman, Lee, et al. Cecil's Textbook of Medicine, 21st edition. Philadelphia: W. B. Saunders Company, 2000.
Noble, John, et al. Textbook of Primary Care Medicine, 3rd edition. St. Louis: Mosby, Inc., 2001.
