title: Odontoid process inclination in normal adults and in an adult population with Chiari malformation Type I.
abstract: OBJECTIVE
  Posterior odontoid process inclination has been demonstrated as a factor associated with Chiari malformation Type I (CM-I) in the pediatric population; however, no studies to date have examined this measurement in the adult CM-I population. The purpose of this study was to evaluate craniocervical junction (CCJ) measurements in adult CM-I versus a control group.
  
  
  METHODS
  The odontoid retroflexion, odontoid retroversion, odontoid height, posterior basion to C-2 line measured to the dural margin (pB-C2 line), posterior basion to C-2 line measured to the dorsal odontoid cortical margin (pB-C2* line), and clivus-canal angle measurements were retrospectively analyzed in adult patients with CM-I using MRI. These measurements were compared with normative values established from CT scans of the cervical spine in adults without CM-I.
  
  
  RESULTS
  A statistically significant difference was found between 55 adults with CM-I and 150 sex-matched controls (125 used for analysis) in the mean clivus-canal angle and the mean pB-C2 line.
  
  
  CONCLUSIONS
  These data suggest that there are sex-specific differences with respect to measurements at the CCJ between men and women, with women showing a more posteriorly inclined odontoid process. There were also differences between the CM-I and control groups: a more acute clivus-canal angle was associated with CM-I in the adult population. These CCJ findings could have an influence on presurgical planning.
authors: Department of Radiology, University of Utah, Salt Lake City, Utah;|US Naval Medical Center Portsmouth, Virginia;
authors: David A
authors: DA
authors: Besachio
authors: Royal Perth Hospital, Perth; and.|Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.
authors: Ziyad
authors: Z
authors: Khaleel
authors: Department of Radiology, University of Utah, Salt Lake City, Utah;
authors: Lubdha M
authors: LM
authors: Shah
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001139:Arnold-Chiari Malformation / Q000000981:diagnostic imaging / Q000473:pathology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000000981:diagnostic imaging / Q000473:pathology*; D012737:Sex Factors; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: CCJ = craniocervical junction; CM = Chiari malformation; CM-I = CM Type I; Chiari malformation; ICC = intraclass correlation coefficient; cervical; complex Chiari malformation; craniocervical junction; odontoid inclination; pB-C2 = a line drawn through the odontoid tip from the ventral dura perpendicular to a second line from the basion to the inferoposterior aspect of the C-2 vertebral body; pB-C2* = a line drawn through the odontoid tip from the posterior odontoid cortex perpendicular to a second line from the basion to the inferoposterior aspect of the C-2 vertebral body