Migraines occur when blood vessels in the head contract and dilate in an abnormal manner. The arteries in the back of the head have been shown to go into spasm, reducing blood flow to the back part of the brain or the occipital lobe. This is thought to trigger the pulsating pain in the side of the head that is seen in migraine.

Stroke also occurs when a part of the brain is deprived of blood. Some studies suggest that there is a link between migraine and stroke or cerebrovascular accident (CVA) and that people who suffer from migraine may be at an increased risk of stroke, particularly women.  

About 15% of the population is affected by migraine and the condition is three times more common among women than in men. The reason why migraine affects women more may be linked to raised estrogen levels as some studies have shown that women report more frequent migraines around the time when they are menstruating.

Studies have also shown that women with migraine who take oral contraceptives are at an increased risk of stroke. Furthermore, women with migraine are more at risk of stroke and heart attack than women who do not experience migraines. The risk of thrombosis and ischemic stroke also appears to be higher among people with migraine. Although the exact mechanism that links migraine and increased stroke risk has not yet been elucidated, research suggests that abnormalities in cerebral vasculature may be involved.

There are two main types of stroke – hemorrhagic and ischemic stroke. Overall, stroke is more common among men than women. However, one study showed that among females, the risk for ischemic stroke was greater among those aged 35 to 45 who suffer form migraines. This risk was further increased by smoking, use of the contraceptive pill and high blood pressure. Hemorrhagic stroke, on the other hand, does not appear to be associated with migraine. 

There is little evidence to show that a person is at an increased risk of stroke while they are experiencing a migraine, although the two conditions have been shown to occur together. The official name for the occurrence of ischemic stroke during a migraine attack is migrainous infarction. Among people who experience a migrainous infarction, aura symptoms are prolonged and evidence of ischemic stroke is revealed by a brain scan.