Table 1:

Normal anatomic relationships of the craniocervical junction on MDCT in 200 patients and comparison with accepted values on plain radiographs*

MethodMeanSDRangeMDCT Normal ValuePlain Radiograph Normal Value2,5,6
BAI3.44.64−8.7–26.0Not reliable<12.0
Powers ratio0.80.080.6–1.2<0.9<1.0
ADI1.30.370.5–2.4<2.0 in both sexes<3.0 men
<2.5 women
AOI1.00.230.5–1.8<1.4No data in adults
  • Note:—MDCT indicates multidetector row CT; BAI; basion-axial interval; BDI, basion-dens interval; ADI, atlantodental interval; AOI, atlanto-occipital interval.

  • * Results are given in millimeters with the exception of the Powers ratio.

  • Normal value is the maximum value for 97.5% of the population.