Normal Wackenheim’s Angle Size on X-ray, CT & MRI
Wackenheim’s angle is a craniocervical junction measurement drawn on lateral imaging between the line along the posterior surface of the clivus and the line along the posterior surface of the odontoid process (dens). It provides a quantitative assessment of the angular relationship at the craniovertebral junction. Accurate measurement is essential for detecting instability, basilar invagination, and other craniocervical anomalies that may endanger the brainstem and upper cervical cord.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | >150¡ |
Clinical Significance
A normal Wackenheim’s angle is greater than 150° on lateral projection. A value at or below this threshold suggests abnormal angulation at the craniocervical junction, which may indicate atlantoaxial instability, basilar invagination, or platybasia. Because the brainstem and upper cervical spinal cord are in close proximity, even subtle malalignment can have profound neurological consequences.
Reduced Wackenheim’s angle is a useful adjunct measurement when other craniocervical metrics — such as the McRae line, Chamberlain’s line, or the atlantodental interval — are borderline. Pitfalls include patient positioning artifacts on lateral radiographs (flexion or extension) and degenerative changes that alter normal bony landmarks, both of which can affect angular measurement accuracy.
- Basilar invagination — superior migration of the dens into the foramen magnum
- Atlantoaxial instability — traumatic, rheumatoid, or congenital etiologies
- Os odontoideum — anomalous ossicle replacing the normal dens
- Down syndrome / skeletal dysplasias — ligamentous laxity causing craniocervical malalignment
- Chiari malformation — often coexists with craniocervical junction anomalies
Reference: Munk PL, Ryan AG. Teaching Atlas of Musculoskeletal Imaging. Thieme. (2007).
Imaging Notes
On lateral radiography, the angle is measured in the neutral position with the patient upright when possible. True lateral positioning is critical; rotational obliquity degrades landmark identification and introduces measurement error. The posterior clival line should be drawn along the dorsal cortex of the clivus, extended to intersect a line drawn along the posterior cortex of the odontoid process.
On CT and MRI, sagittal midline reconstructions provide optimal visualization of both the clivus and dens. CT offers superior cortical bone detail for precise angular measurement, while MRI additionally demonstrates soft-tissue and neural element involvement. On MRI, the posterior clival and odontoid cortices remain identifiable on T1-weighted sequences and should be measured consistently in the same plane used for radiographic assessment.