Both conditions are characterized by increased proximity of the cranial cervical spine to the base of the skull [25]; however a defining characteristic of human basilar invagination is invagination of the odontoid process of the axis through or towards the foramen magnum, often with compression of the neural tissue by the dens [25]. (journals.plos.org)
To determine whether there was any increased risk of stroke in basilar and hemiplegic patients taking triptans or DHE, Klein and researchers at Brigham and Women's Hospital in Boston did a retrospective analysis, collecting data from four headache centers around the country. (sciencedaily.com)