Positron emission tomography studies in headache

Positron emission tomography (PET) allows the quantitative measurement of regional cerebral flow (rCBF) in humans in quantitative terms. Gross changes in rCBF are due to variation in vessel diameter. Changes of rCBF also reflect synaptic activity (inhibition and excitation). Therefore, PET was used to monitor changes in blood flow during the aura and headache phase of a migraine attack and to investigate focal areas of increased or decreased blood flow, e.g., in the brain stem and midbrain. Hemispheric rCBF was unchanged in spontaneous migraine attacks without aura. This was true for the headache side as well as for the nonheadache side. Sumatriptan had no effects on cerebral blood flow. Regional cerebral blood flow was increased in midline brain stem structures during the headache phase, but also when the headache had been treated with sumatriptan. This persisting increased activity might reflect activity of a presumed migraine center in the brain stem. These changes are specific for migraine attacks and are not seen during attacks of cluster headache. Positron emission tomography measurements in the early phase of a migraine attack in a single subject showed flow reductions in the occipital cortex spreading forwards; an observation which would be compatible with the existence of spreading depression in humans. Our attempts to study the aura phase with PET have, to date, been unsuccessful.