Migraine headaches affect an estimated 28 million Americans and are associated with increased risk of ischemic stroke. It was once believed that migraine was caused by dilation of blood vessels in the head, and more recently it has been attributed to anomalous neuron signals.

Now, in a study from the University of Pennsylvania, researchers propose that blood vessels play a different role than previously thought. Structural alterations of the blood supply to the brain may increase susceptibility to changes in cerebral blood flow, contributing to the abnormal neuronal activity that starts migraine.

The supply of blood to the brain is protected by a series of connections between the major arteries. Referred to as the circle of Willis after the English physician who first described it, people with migraine, and especially those with migraine with aura, are more likely to be missing components of the circle of Willis.

The Circle of Willis

“People with migraine actually have differences in the structure of their blood vessels - this is something you are born with,” said Dr. Brett Cucchiara, the study’s lead author and Professor of Neurology. “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."

The study involved 170 people from three groups.

There was a control group with no headaches, those who had migraine with aura, and those who had migraine without aura. Researchers found that an incomplete circle of Willis was more common in people with migraine with aura (73 percent) and migraine without aura (67 percent), compared to a headache-free control group (51 percent).

Magnetic resonance angiography was used by the team to scrutinize blood vessel structure. To measure changes in cerebral blood flow, a non-invasive magnetic resonance imaging method pioneered at the University of Pennsylvania, called Arterial spin labeling was used.

“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. This may help explain why the most common migraine auras consist of visual symptoms such as seeing distortions, spots, or wavy lines,” said senior author Dr. John Detre.

Both migraine and an incomplete circle of Willis are commonplace, and the link between the two is probably only one of many factors that contribute to migraine in any individual.

The researcher team suggested that at some point diagnostic tests of circle of Willis integrity and function could help pinpoint this contributing factor in an individual patient. Treatment strategies might then be personalized and tested in specific subgroups.


  1. Migraine with Aura Is Associated with an Incomplete Circle of Willis: Results of a Prospective Observational Study Brett Cucchiara, Ronald L. Wolf, Lidia Nagae, Quan Zhang, Scott Kasner, Ritobrato Datta, Geoffrey K. Aguirre, John A. DetreResearch Article | published 26 Jul 2013 | PLOS ONE10.1371/journal.pone.0071007

  2. Buring JE, Hebert P, Romero J, Kittross A, Cook N, et al. (1995) Migraine and subsequent risk of stroke in the Physicians' Health Study. Arch Neurol 52: 129–134. doi: 10.1001/archneur.1995.00540260031012.

Photo: Jef Safi/Flickr

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