Diagnosis & Imaging
Basion-dens interval (BDI)
The basion-dens interval is a measurement of the distance between the skull base and the top of the odontoid, used to assess craniocervical alignment and stability.
In short: Basion-dens interval (BDI)
- It measures the distance from the basion to the top of the odontoid (dens).
- It helps assess craniocervical alignment and stability.
- An abnormal value can indicate instability or abnormal alignment.
- It is one of several craniometric measurements.
What it is
The basion-dens interval (BDI) is the measured distance between the basion (the front edge of the foramen magnum) and the top of the odontoid process (the dens). It is used to assess the alignment and stability of the craniocervical junction.
Understanding Basion-dens interval (BDI)
The BDI reflects the vertical relationship between the skull base and the top of the second vertebra. An abnormally increased BDI can suggest craniocervical instability or abnormal separation (distraction) between the skull and spine, while other patterns can indicate different abnormalities. In the context of Chiari, the BDI is one of the craniometric measurements used to evaluate the craniocervical junction for instability or abnormal alignment — relevant because such findings (often in people with connective-tissue conditions) can change management, sometimes requiring fusion. The BDI is used together with other measurements (such as the basion-axial interval) for a complete assessment. Understanding the basion-dens interval clarifies one of the measurements used to assess craniocervical alignment and stability in Chiari.
Why it matters
Understanding the basion-dens interval helps families see how the vertical relationship between the skull and spine is measured to assess for instability or abnormal alignment — relevant in Chiari evaluation and treatment decisions.
Common questions
What is the basion-dens interval?
The distance from the basion to the top of the odontoid.
What does it assess?
Craniocervical alignment and stability.
Why does it matter?
Abnormal values can indicate instability, which can change management.
Bottom line
The basion-dens interval measures the distance from the skull base to the top of the odontoid, assessing craniocervical alignment and stability in Chiari.
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