Brain and craniovertebral junction in patients with achondroplasia using low dose dynamic computed tomography

Purpose: To describe the brain and craniovertebral junction (CVJ) in achondroplasia by dynamic low dose computed tomography (CT). Methods: This paper documents a cross-sectional retrospective study performed between 1998 and 2013. The Ethics and Research Committee approved the project. The investigators reviewed the medical records of 440 patients with skeletal dysplasia and performed flexion-extension CT for 24 patients with achondroplasia confirmed by molecular testing. They were divided in two groups: children younger than eight years old and group 2 with older individuals. Normal scans were selected as controls in proportion 1:4. Three measurements were made by two radiologists using the following parameters: Evans Ratio, cerebroventricular index of the anterior horns and maximum width of the third ventricle; diameters of the foramen magnum (FM), width of the spinal canal, clivus size, basion-axial interval, atlantooccipital interval and Powers ratio, atlantodental interval, distance of the dens tip position above McGregor line and Welcher angle. T-test, Kruskal-Wallis and Fisher statistics were used. P-value<0.05 threshold was considered for statistical significance. Results: The ventricles were greater, and the FM was smaller in achondroplastic patients than in controls scans (p<0.01). Other findings were: ventriculomegaly (30%), hydrocephalus (4%), narrowing of FM (between 96% and 100%), spinal stenosis (92%), clivus hypoplasia (88%), atlantooccipital instability (25%), atlantoaxial instability (13 %), basilar invagination (13%) and platybasia (8%). There was no upper cervical compressive myelopathy. There was no difference of CVJ changes between the groups 1 and 2 (p>0.09). Conclusion: The craniometry showed the most frequent cerebral and CVJ changes in achondroplasia.