There can be no doubt that migraine is associated with changes in the cephalic (cerebral and non-cerebral) circulation; the doubts, however, concern the cause and nature of such changes. In a majority of migraine patients with 'aura', the cerebral blood flow decreases, but in 'classical' migraine patients both decreases and increases have been reported. In the non-cerebral cephalic circulation, vasodilatation and increased pulsations are observed principally on the side of the migraine headache, but the idea of simple vasodilatation is paradoxical to the facial pallor and laxity of tissues usually noticed during the headache. To resolve this paradox, Heyck suggested that vasodilatation involves cephalic arteriovenous anastomoses.

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Erasmus MC: University Medical Center Rotterdam

Saxena, P. R. (2012). Is there still a case for the shunt hypothesis in migraine?. doi:10.1093/acprof:oso/9780192618108.003.0015