Definition of Vertebrobasilar circulatory disorders:

Vertebrobasilar circulatory disorders are disorders in which blood supply to the back of the brain is disrupted.

Causes, incidence, and risk factors:

The vertebrobasilar system is also called the posterior (back) circulation of the brain. There are 3 main blood vessels that provide circulation to the back of the brain -- 2 vertebral arteries and 1 basilar artery.

The back of the brain contains structures that are crucial for sustaining life. For instance, the brainstem controls breathing, 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 (movement coordination).

Blood flow in the posterior circulation of the brain may be disrupted by many different conditions. The most common cause is a stroke caused by hardening of the arteries (atherosclerosis).

Atherosclerosis occurs when fat accumulates in a blood vessel wall, causing local inflammation (irritation and swelling). The areas of inflammation are called plaques, and they may break off and cause blood clots inside the vessel.

These clots may then travel inside the arteries and get stuck in the brain, blocking the blood supply to the area normally fed by the artery. This sudden stopping 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 a certain type of stroke.

Vertebrobasilar vascular disorders may also be caused by 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 fibromuscular dysplasia), or 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 and vasculitis.