title: Anatomic relationship of the internal carotid artery to the C1 vertebra: A case report of cervical reconstruction for chordoma and pilot study to assess the risk of screw fixation of the atlas.
abstract: METHODS
  A case of internal carotid artery impingement by the tip of a well-positioned C1-C2 transarticular screw is presented along with a pilot study involving radiologic and anatomic evaluation of human cadaveric specimens.
  
  
  OBJECTIVE
  To raise awareness that the internal carotid artery may be in close proximity to the anterior aspect of the atlas and at risk of injury during placement of C1-C2 transarticular screws or C1 lateral mass screws.
  
  
  BACKGROUND
  To our knowledge, no cases of internal carotid artery injury or impingement have been reported with screw fixation of the atlas.
  
  
  METHODS
  A case of internal carotid artery impingement by a C1-C2 transarticular screw is presented. The C1-C2 rotation appeared to place the internal carotid artery in the path of the screw, prompting a pilot study. Three fresh-frozen human cadaveric head and neck specimens were fixed in different degrees of rotation. Thin-section computed tomography of the specimens was obtained in the plane of the atlas. The frozen specimens were sectioned in the same plane as the computed tomography images. Measurements were taken to assess the location of the internal carotid artery relative to the anterior aspect of the atlas.
  
  
  RESULTS
  Cervical rotation does not have a predictable effect on the location of the internal carotid artery. Medial angulation of a screw placed in the lateral mass of C1 appears to increase the margin of safety for the internal carotid artery. The internal carotid artery varies in location and may be within 1 mm of the ideal exit point of a bicortical transarticular screw or a C1 lateral mass screw.
  
  
  CONCLUSIONS
  The internal carotid artery is at risk during bicortical screw fixation of the atlas. We recommend a contrast-enhanced computed tomography to assess the location of the internal carotid artery before screw fixation of the atlas.
authors: Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota 55905, USA. currier.bradford@mayo.edu
authors: Bradford L
authors: BL
authors: Currier
authors: Larry T
authors: LT
authors: Todd
authors: Timothy P
authors: TP
authors: Maus
authors: Dean R
authors: DR
authors: Fisher
authors: Michael J
authors: MJ
authors: Yaszemski
mesh_terms: D000293:Adolescent; D001863:Bone Screws / Q000009:adverse effects*; D020212:Carotid Artery Injuries / Q000209:etiology; D002343:Carotid Artery, Internal / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000601:surgery*; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000601:surgery*; D002817:Chordoma / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D010865:Pilot Projects; D018570:Risk Assessment; D013125:Spinal Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed