[The trigeminovascular system in the human. Cerebral blood flow, functional imaging and primary headache]

Primary headache syndromes, such as cluster and migraine, are widely described as vascular headaches, even though there is considerable clinical evidence to suggest that both conditions are primarily central, that is regulated by the brain. The shared anatomical and physiological substrate for both clinical syndromes is the neural innervation of the cranial circulation. Early functional imaging using PET has shed light on the genesis of both syndromes, documenting activation in the midbrain and pons in migraine and in the hypothalamic gray in cluster headache. These areas are involved in the pain process in a permissive or triggering manner rather than simply as a response to first-division nociceptive pain impulses. This article reviews findings in the physiology of the trigeminovascular system which demand renewed consideration of the neural influences in many primary headaches and the physiology of the neural innervation of cranial circulation. Primary headaches should thus be regarded as neurovascular headaches to emphasize the interaction between nerves and vessels which is their underlying characteristic.