Etiology and pathogenesis of cluster headache.

This last decade has seen remarkable progress made toward unraveling the mystery of primary headache disorders like migraine and cluster. The vascular theory has been superseded by recognition that neurovascular phenomena seem to be the permissive and triggering factors in migraine and cluster headache. This understanding has been achieved through new imaging modalities such as positron emission tomography and functional magnetic resonance imaging. Prior to these imaging techniques it was impossible to study the primary headache disorders because these had no structural basis. There is now an increasing body of evidence that the brain is involved primarily in cluster and migraine and that vessel dilatation is an epiphenomenon.