The clinical features and pathogenesis of headache associated with Chiari-I malformation and syringomyelia are reviewed from the Katholieke Universiteit Leuven, Belgium. The incidence of headache reported with Chiari-I malformation has varied from 12 to 58%. In a retrospective review of 62 cases of syringomyelia, only two had headache as a presenting symptom. Chiari-I headache is paroxysmal or protracted, occipital in location, aggravated by Valsalva’s maneuver, effort, cough, and postural changes, and correlates with the degree of tonsillar herniation. Syringomyelia may coexist with Chiari-I malformation, but has no relation to the occurrence of headache. The cause of the headache is uncertain, but probably related to the tonsillar herniation. Intermittent obstructive hydrocephalus, with increased intracranial pressure, irritation of meninges at the foramen magnum, compression of upper cervical roots, and involvement of the descending nucleus of the trigeminal nerve are some of the possible causes of pain with Chiari-I malformation. 
COMMENT. A herniation of 5 mm is considered pathological and 3-5 mm is borderline. Minimal degrees of tonsillar herniation discovered by MRI in children with migraine type headaches is of concern and requires follow-up. Chiari-I headache may present at puberty or during first pregnancies. Hormonal changes may accentuate the tonsillar herniation and precipitate symptoms. (Progress in Pediatric Neurology II, PNB Publ, 1994;pp158-9).