MRI of intracranial arteries in nitroglycerin induced cluster headache attacks.

Eight patients with episodic cluster headache, five in active episode, three out of episode, were investigated as to diameters of intracranial arteries before and after nitroglycerin (NG) administration. The diameter of all intracranial carotids were increased about 10 minutes after NG, although more in the patients in episode than in patients out of episode. The dilatation remained for the next 60 minutes in the patients who did not get a cluster headache attack. There was a normalization of the diameters of the internal carotid arteries compared to the initial values, at maximum pain in all patients who got a cluster headache attack. Similar changes were also found in the basilar arteries. The findings support the hypothesis of a constriction of intracranial arteries at maximum pain in cluster headache attacks to stop the pain.