Basion
Pronunciation: BAY-see-on
The most inferior point on the anterior margin of the foramen magnum, used as a posterior cranial base landmark in cephalometric analysis.
Full Definition
Basion (abbreviated Ba) is a skeletal cephalometric landmark at the midpoint of the anterior border of the foramen magnum of the occipital bone. It defines the posterior limit of the cranial base and is used in measurements such as the Ba-N line, which establishes the anterior cranial base reference. In editorial contexts it appears in cephalometric landmark lists and surgical planning documents. Editors should note it is distinct from Sella, the more commonly used anterior cranial base landmark. Misrendering as 'basion' (lowercase) when used in a list of proper cephalometric points is a common styling error.
Usage
Usage note: Capitalise as a proper landmark name in cephalometric contexts. Do not confuse with Nasion (anterior cranial base) or Sella (midpoint of the sella turcica).
In Context
- "The Ba-N distance confirmed a shortened anterior cranial base in this brachycephalic patient." — Cephalometric research article
- "Basion was identified on the lateral cephalogram before the cranial base angle was calculated." — Orthodontic case report