title: Posterior fossa measurements in patients with and without Chiari I malformation.
abstract: OBJECTIVE
  To determine if there is a correlation between cerebellar tonsillar descent in patients with and without Chiari I malformation and three skull morphometric measurements: clivus length, anteroposterior diameter of the foramen magnum, and Boogard's angle.
  
  
  METHODS
  Cerebellar tonsillar descent, clivus length, anteroposterior diameter of the foramen magnum, and Boogard's angle were measured in mid-sagittal T1-weighted magnetic resonance images of 188 patients. The study included 81 patients with Chiari I malformations (CMI). Without identifiable pathology, 107 patients served as a comparison group. Two-sample t-tests were used to assess for significance. A Pearson correlation matrix was constructed to assess the strength of linear dependence between measured parameters for the study population.
  
  
  RESULTS
  A negative correlation was found between tonsillar herniation and clivus length (r = -0.30, P < 0.001), while a positive correlation was found between tonsillar herniation and foramen magnum size (r = 0.15, P = 0.0431), and Boogard's angle (r = 0.23, P = 0.0014). Clivus length was shorter (P = 0.0009) in CMI patients (4.02 cm ± 0.45) than comparison patients (4.23 cm ± 0.42). In addition, the anteroposterior diameter of the foramen magnum was wider (P = 0.0412) (3.74 cm ± 0.40 compared to 3.63 ± 0.30) and Boogard's angle was larger (P = 0.0079) (123.58 degrees ± 8.27 compared to 120.62 degrees ± 6.79) with CMI.
  
  
  CONCLUSIONS
  A greater degree of cerebellar tonsillar herniation is associated with a shorter clivus length, a wider anteroposterior diameter of foramen magnum, and a wider Boogard's angle.
authors.affiliation: Department of Diagnostic Radiology, Kingston General Hospital, Queen's University, Toronto, Ontario, Canada.
authors.forename: John A
authors.initials: JA
authors.lastname: Dufton
authors.forename: Syed Yaser
authors.initials: SY
authors.lastname: Habeeb
authors.forename: Manraj K S
authors.initials: MK
authors.lastname: Heran
authors.forename: David J
authors.initials: DJ
authors.lastname: Mikulis
authors.forename: Omar
authors.initials: O
authors.lastname: Islam
mesh_terms: D000328:Adult; D000368:Aged; D002640:Chiari-Frommel Syndrome / Q000473:pathology*; D005260:Female; D005539:Foramen Magnum / Q000473:pathology*; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult