title: The intracranial entrance of the atlantal segment of the vertebral artery in crania with occipitalization of the atlas.
abstract: OBJECTIVE
  An anomalous vertebral artery (VA) position can jeopardize an otherwise successful procedure, such as a posterior cranial fossa decompression for hindbrain herniation, and may increase the propensity for VA occlusion.
  
  
  METHODS
  The authors describe the detailed anatomy of the entrance site of the VA in adult human crania in which there is occipitalization of the atlas. They found that if the atlantal posterior arch or hemiarch was fused to the occiput one should anticipate encountering an anomalous osseous pathway as the VA enters into the cranium, as evidenced by this finding in 80% of their specimens. An anomalous entry pathway was present in all but one left-sided specimen in which the left posterior hemiarch was not fused to the occiput and one right-sided specimen in which there was an unfused and rudimentary posterior arch of the atlas.
  
  
  CONCLUSIONS
  The clinician should consider the possibility that the VA takes anomalous routes into the skull in cases in which there is occipitalization of the atlas.
authors.affiliation: Department of Cell Biology, University of Alabama at Birmingham, and Pediatric Neurosurgery, Children's Hospital, Birmingham, Alabama, USA. rstubbs@uab.edu
authors.forename: R Shane
authors.initials: RS
authors.lastname: Tubbs
authors.forename: E George
authors.initials: EG
authors.lastname: Salter
authors.forename: W Jerry
authors.initials: WJ
authors.lastname: Oakes
mesh_terms: D001268:Atlanto-Axial Joint / Q000033:anatomy & histology*; D002102:Cadaver; D006801:Humans; D012886:Skull / Q000033:anatomy & histology*; D014711:Vertebral Artery / Q000033:anatomy & histology*