A migraine headache is an often familial symptom complex of periodic attacks of vascular headache, usually temporal and unilateral in onset, commonly associated with irritability, nausea, vomiting, constipation or diarrhea and often photophobia, attacks are preceded by constriction of the cranial arteries, usually with resultant prodromal sensory (especially ocular) symptoms and commence with the vasodilation that follows.

(Origin: Gr. hemikrania = an affection of half of the head.)