The most common type of vascular headache is migraine. Migraine headaches are usually characterized by severe pain on one or both sides of the head, an upset stomach and at times disturbed vision.

Symptoms of migraine.
Sensitivity to light is a standard symptom of the two most prevalent types of migraine-caused headache: classic and common.

The major difference between the two types is the appearance of neurological symptoms ten to 30 minutes before a classic migraine attack. These symptoms are called an aura. The person may see flashing lights or zigzag lines or may temporarily lose vision. Other classic symptoms include speech difficulty, weakness of an arm or leg, tingling of the face or hands and confusion.

The pain of a classic migraine headache is described as intense, throbbing or pounding and is felt in the forehead, temple, ear, jaw or around the eye. Classic migraine starts on one side of the head but may eventually spread to the other side. An attack lasts one to two pain-wracked days.

The common migraine--a term that reflects the disorder's greater occurrence in the general population--is not preceded by an aura. But some people experience a variety of vague symptoms beforehand, including mental fuzziness, mood changes, fatigue and unusual retention of fluids. During the headache phase of a common migraine, a person may have diarrhea and increased urination, as well as nausea and vomiting. Common migraine pain can last three or four days.

Both classic and common migraine can strike as often as several times a week, or as rarely as once every few years. Both types can occur at any time. Some people, however, experience migraines at predictable times near the days of menstruation or every Saturday morning after a stressful week of work.

The migraine process.
Research scientists are unclear about the precise cause of migraine headaches. There seems to be general agreement, however, that a key element is blood flow changes in the brain. People who get migraine headaches appear to have blood vessels that overreact to various triggers.

Scientists have devised one theory of migraine that explains these blood flow changes and also certain biochemical changes that may be involved in the headache process. According to this theory, the nervous system responds to a trigger such as stress by creating a spasm in the nerve-rich arteries at the base of the brain. The spasm closes down or constricts several arteries supplying blood to the brain, including the scalp artery and the carotid or neck arteries.

As these arteries constrict, the flow of blood to the brain is reduced. At the same time, blood-clotting particles called platelets clump together--a process that is believed to release a chemical called serotonin. Serotonin acts as a powerful constrictor of arteries, further reducing the blood supply to the brain.

Reduced blood flow decreases the brain's supply of oxygen. Symptoms signaling a headache, such as distorted vision or speech, may then result, similar to symptoms of stroke.

Reacting to the reduced oxygen supply, certain arteries within the brain open wider to meet the brain's energy needs. This widening or dilation spreads, finally affecting the neck and scalp arteries. The dilation of these arteries triggers the release of pain-producing substances called prostaglandins from various tissues and blood cells. Chemicals which cause inflammation and swelling, and substances which increase sensitivity to pain are also released. The circulation of these chemicals and the dilation of the scalp arteries stimulate the pain-sensitive nociceptors. The result, according to this theory: a throbbing pain in the head.