The vertebrobasilar system is also called the "posterior circulation" of the brain. There are three main vessels which provide circulation to the back of the brain -- two vertebral arteries and one basilar artery.
The back of the brain contains structures which are crucial for sustaining life. For instance, the brainstem controls respiration, swallowing, and the level of consciousness. Other structures of the back of the brain are the occipital lobes (the vision areas of the brain) and the cerebellum (which controls motor coordination).
Blood flow in the posterior circulation of the brain can be disrupted by many different conditions. The most common cause is stroke caused by hardening of the arteries (atherosclerosis).
This can occur when fat accummulates in a blood vessel wall, causing local inflammation (irritation and swelling with presence of extra immune cells). The areas of inflammation are called "plaques," and they can break off and cause blood clots inside of the vessel.
These clots can then travel inside the arteries and get stuck in the brain, blocking the blood supply to the area normally fed by the artery. This abrupt stop of blood supply causes rapid malfunction and even death of the affected brain cells, which are very sensitive to lack of circulation. This is what happens when a person suffers one type of stroke.
VCD also can be caused by so-called "dissection," which is a tear of the artery wall. This involves bleeding through the artery wall and sometimes the release of a clot which then blocks blood flow.
Dissection can be caused by plaques, other diseases of the arteries (such as "fibro-muscular dysplasia"), or it can be caused by trauma (such as a car accident). It may even be caused by manipulations of the neck by a chiropractor or during massage.
However, most of the time, no apparent cause of dissection can be identified. Other less common causes of vertebrobasilar vascular disorders include connective tissue diseases (for instance lupus and other forms of arthritis) or vasculitis.
