Clivo-axial angle (CXA)

What it is

The clivo-axial angle (CXA, also called the clival-axial or clivus-canal angle) is the angle formed between the clivus (the sloped skull-base bone) and the upper cervical spine (the axis). It is used to assess for abnormal craniocervical alignment and ventral brainstem compression.

Understanding Clivo-axial angle (CXA)

The CXA reflects the alignment between the skull base and the upper spine. A normal angle allows the brainstem to pass without kinking; an abnormally sharp or "kyphotic" angle (the spine angling forward relative to the clivus) can indicate ventral brainstem compression or kinking — a feature of complex Chiari. An abnormal CXA is associated with symptoms and, along with other measurements (such as the pB-C2 line), can help predict craniocervical instability and guide whether additional surgery (such as fusion to correct alignment) is needed. The CXA is one of the key craniometric measurements in evaluating complex craniocervical situations. Understanding the clivo-axial angle clarifies a measurement of craniocervical alignment relevant to brainstem compression in Chiari.

Why it matters

Understanding the clivo-axial angle helps families see how the alignment between the skull base and upper spine is measured to detect brainstem compression or kinking — relevant in complex Chiari and decisions about fusion.