- Stenosis at the foramen magnum
- Generalized spinal canal stenosis
- Foramen magnum stenotic: The rim of the foramen magnum is thick, resulting in a narrow foramen. The narrow foramen magnum means that the vertebral arteries are closer to the midline.
- Midline keel: There is a thick midline keel extending up from the foramen magnum.
MRI in Achondroplasia
- Loss of CSF space: The CSF spaces at the cervicomedullary junction are effaced.
- T2-weighted changes in spinal cord: T2-weighted signal change is present in more than 50% of cases at the time of surgical decompression (17).
- Instability rare: Cervical instability is rare in achondroplasia, either at presentation or as a result of decompression.