Vertebrobasilar InsufficiencyVertebral ArterySubclavian Steal SyndromeSubclavian ArteryBasilar ArteryVertigoCerebral AngiographyArterial Occlusive DiseasesAdrenal InsufficiencyRenal InsufficiencyVenous InsufficiencyIntracranial AneurysmExocrine Pancreatic InsufficiencyVertebral Artery DissectionPlacental InsufficiencyMagnetic Resonance AngiographyAngiography, Digital SubtractionInfarction, Posterior Cerebral ArteryIschemic Attack, TransientIntracranial ArteriosclerosisPetrous BoneTrigeminal NeuralgiaEchoencephalography