An incomplete network of arteries that supply blood to the brain could be a culprit for migraine headaches. A study recently published in PLOS ONE reveals that variations in the brain’s arteries cause inconsistent blood flow, which may trigger migraines.

Researchers from the University of Pennsylvania were particularly interested in a set of connections between major arteries that protect the supply of blood to the brain. These connections are called the “circle of Willis,” named after the English doctor who first described it in the 1600s.

The researchers studied 170 people in three groups:

  • 53 people with no headaches acting as a control group
  • 56 who had migraine with aura, a perceptual disturbance
  • 61 people who had migraine without aura.

The team, led by Dr. Brett Cucchiara, measured changes in brain blood flow using magnetic resonance angiography to analyze the blood vessel structure of the subjects, as well as an MRI method called Arterial spin labeling (ASL).

Of the people in the study who suffered from migraine with aura, 73% had an incomplete circle of Willis, as did 67% of people who had migraines without aura. This compared with 51% of the healthy controls who did not get migraine headaches.

Dr. Cucchiara says:

People with migraine actually have differences in the structure of their blood vessels – this is something you are born with.

These differences seem to be associated with changes in blood flow in the brain, and it’s possible that these changes may trigger migraine, which may explain why some people, for instance, notice that dehydration triggers their headaches.”

Around 28 million people in the US suffer from migraines that impair them in some way, the study authors say. And aside from headache-related disabilities, migraine with aura has been linked to an increased risk of ischemic stroke.

Though circle of Willis variations are linked to changes in blood flow within the brain, only about 40-50% of normal subjects have a complete circle, according to the researchers.

Migraine brain diagram - circle of Willis

A) Anatomy of the circle of Willis B) Complete circle C) Incomplete circle. Courtesy: Penn Medicine/Brett Cucchiara/John Detre

Dr. John Detre, the study’s senior author, adds: “Abnormalities in both the circle of Willis and blood flow were most prominent in the back of the brain, where the visual cortex is located.” He says the location of abnormalities may provide an insight into why many migraines accompanied by visual disturbances, such as spots or wavy lines.

Since migraines and an incomplete circle of Willis are quite common, the researchers note that the link they observed in their study is most likely just one of several factors that result in migraines in individuals.

They recommend that future tests for function of the circle of Willis could help doctors diagnosing patients with chronic migraines. They hope their findings will help toward personalized treatment strategies for migraine patients.