Basion-dens interval

Dr Owen Kang and Dr Craig Hacking et al.

The basion-dens interval (BDI), as the name suggests, is the distance between the basion and the tip of the dens, used in the diagnosis of atlanto-occipital dissociation injuries.

It is the distance from the most inferior portion of the basion to the closest point of the superior aspect of the dens in the median (midsagittal) plane.

Normal values are <12 mm on plain radiographs and <8.5 mm on CT 1.

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Article information

rID: 40481
Section: Gamuts
Synonyms or Alternate Spellings:
  • BDI
  • Basion-dens interval (BDI)

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Cases and figures

  • Base of skull lines (annotated images)
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