I have a friend with throat cancer. The carotid artery is involved. Can a person live with one carotid artery?

K.J.

The brain cannot survive without a rich supply of arterial (oxygenated) blood. Four major arteries carry oxygenated blood to the brain: the paired (left and right) carotid arteries and the paired vertebral arteries. The carotid arteries have a larger caliber than the vertebral arteries and supply a greater proportion of blood to the brain.

Before the vertebral arteries reach the brain, they unite to form the basilar artery. The basilar artery and carotid arteries feed into a more-or-less circular network of vessels called the circle of Willis, or circulus arteriosus (circle of arteries). Are you familiar with traffic circles? Imagine a very large traffic circle fed by three major highways, with eight exits. In this analogy, the on-ramps (the three major highways feeding the circle) are the two carotid arteries and the basilar artery; the off-ramps are the vessels that supply blood to different areas of the brain.

If a person is born with an anatomically correct circle of Willis, then it is usually possible to remove one carotid artery without impairing blood flow to the brain. The basilar artery and the remaining carotid artery will supply sufficient blood flow to the circle to provide plenty of blood to the "off-ramps."

Unfortunately, some people do not have an anatomically intact circle of Willis. Loss of one carotid artery in such individuals may lead to a lack of blood flow to a portion of the brain; this is a stroke. The patient may sustain a variety of neurologic impairments. In some cases, there could even be a fatal shortfall of blood to the brain.

How can your friend's surgeon know whether the carotid artery can be safely removed? One of the best methods is known as a balloon occlusion study. A slender catheter is threaded (via a large artery in the groin) into the cancerous carotid artery. At the end of this catheter is an inflatable balloon. Once the catheter is in an appropriate position within the carotid, the balloon is inflated, blocking the flow of blood. The patient is usually awake during this procedure. A neurologic exam can be performed while the balloon is inflated to determine whether the patient is suffering any impairments. Also, the patient's EEG ("brain waves"-- the electrical activity of the brain) can be monitored to find subtle deficits. If there are serious problems, the balloon is promptly deflated and blood flow through the carotid is restored. If the patient has no problems while the balloon is inflated, then the surgeon infers that it is safe to remove this carotid artery.

What if your friend's carotid artery cannot be removed? The carotid can be bypassed, much as one would perform bypass surgery for the coronary arteries that supply the heart. If there is only a very small area in which cancer has adhered to the carotid, the surgeon may choose instead to treat this residual disease with postoperative radiation therapy.