title: Variance of cervical vertebral artery measured by CT angiography and its influence on C7 pedicle anatomy.
abstract: METHODS
  Observational study using a retrospective single-institute database.
  
  
  OBJECTIVE
  To investigate the variance of the vertebral artery (VA) V2 segment and the anatomical features of the C7 pedicle with or without VA entry based on computed tomographic (CT) angiography in 919 consecutive Japanese subjects.
  
  
  BACKGROUND
  Generally, the level of the VA entrance into the transverse foramen is assumed to be C6. Therefore, surgeons tend to pay less attention to VA injury when inserting a C7 pedicle screw. However, anomalies at C7 surely exist and are considered to be 1 of the major risk factors for VA injury during posterior instrumentation.
  
  
  METHODS
  Subjects who underwent contrast-enhanced CT or CT angiography from November 2011 to October 2012 were eligible. The entrance into the transverse foramen was reviewed. In addition, anatomical features of C7 with or without VA entrance were measured.
  
  
  RESULTS
  A total of 919 subjects with a mean age of 56.1 years were surveyed. From among 1838 VA courses, VA entered the C6 transverse foramen in 95.6% of specimens (1757 of 1838 VA courses). Sixty-seven of 919 subjects (7.3%) had a unilateral anomaly and 7 (0.8%) had a bilateral anomaly. An abnormal level of entrance was observed in 8.1% of subjects (74 of 919 patients), and 4.4% of specimens (81 of 1838 VA courses), with a level of entrance into the C4, C5, or C7 transverse foramen in 0.5% (n = 10), 3.1% (n = 57), and 0.8% (n = 14) of all specimens, respectively. C7 transverse foramen with a VA entrance was wider in those without a VA entrance, and abnormal cases frequently showed an uneven transverse foramen. Therefore, the C7 pedicle diameter with abnormal VA entrance was significantly narrower in those without VA entrance (P < 0.01; t test).
  
  
  CONCLUSIONS
  CT angiography is recommended in cases with an uneven transverse foramen for confirming vascular anomaly.
  
  
  METHODS
  2.
authors.affiliation: Departments of *Spine Center and †Orthopedic Surgery, Aichi Medical University, Nagakute, Aichi, Japan.
authors.forename: Norimitsu
authors.initials: N
authors.lastname: Wakao
authors.forename: Mikinobu
authors.initials: M
authors.lastname: Takeuchi
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Kamiya
authors.forename: Masahiro
authors.initials: M
authors.lastname: Aoyama
authors.forename: Atsuhiko
authors.initials: A
authors.lastname: Hirasawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Sato
authors.forename: Masakazu
authors.initials: M
authors.lastname: Takayasu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000033:anatomy & histology* / Q000098:blood supply / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D014711:Vertebral Artery / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D055815:Young Adult