title: CT evaluation of Chamberlain's, McGregor's, and McRae's skull-base lines.
abstract: OBJECTIVE
  To evaluate the mean distance from the odontoid process of C2 to the standard skull-base lines (Chamberlain's, McGregor's, and McRae's lines) on computed tomography (CT) imaging. To compare these measurements to previously documented plain radiograph and magnetic resonance imaging (MRI) measurements.
  
  
  METHODS
  Reformatted midline sagittal CT images of 150 adults were retrospectively evaluated. The shortest perpendicular distance was measured from the Chamberlain's, McGregor's and McRae's baselines for each subject to the odontoid tip. Statistical analysis was performed to compare the CT data with the previously obtained MRI and plain film data.
  
  
  RESULTS
  The mean position of the odontoid process was 1.4mm below Chamberlain's line (median 1.2 mm, SD 2.4 mm), 0.8 mm (median 0.9 mm, SD 3 mm) below McGregor's line and 5 mm (median 5 mm, SD 1.8 mm) below McRae's line. There is no significant difference between male and female results (p>0.05) or between these CT and previous MRI measurements (p>0.05).
  
  
  CONCLUSIONS
  These results provide the mean and range of normal distance from the odontoid process to the most frequently used skull-base lines on the current population on CT.
authors.affiliation: Department of Radiology, University College Hospital, Galway, Ireland. carmelcronin2000@hotmail.com
authors.forename: C G
authors.initials: CG
authors.lastname: Cronin
authors.forename: D G
authors.initials: DG
authors.lastname: Lohan
authors.forename: J N
authors.initials: JN
authors.lastname: Mhuircheartigh
authors.forename: C P
authors.initials: CP
authors.lastname: Meehan
authors.forename: J
authors.initials: J
authors.lastname: Murphy
authors.forename: C
authors.initials: C
authors.lastname: Roche
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry / Q000379:methods; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D012016:Reference Values; D012189:Retrospective Studies; D019291:Skull Base / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult