Evaluation of the craniocervical junction in Down syndrome: correlation of measurements obtained with radiography and MR imaging.

Measurement of the atlas-dens interval is the radiographic standard for identification of patients with Down syndrome at high risk for neurologic injury from spinal cord compression. In 17 pediatric patients with Down syndrome, measurements of the atlas-dens interval, distance between the clivus and posterior odontoid process, and width of the neural canal obtained with plain radiographs were compared to predict the width of the subarachnoid space on magnetic resonance (MR) images. In all patients, cervical radiography and craniocervical MR imaging were prospectively performed during lateral flexion and extension. The width of the subarachnoid space was measured with MR imaging. When the 95% confidence interval for correlation coefficients of regression was used, subarachnoid space width on MR images correlated with neural canal width on radiographs better than with either atlas-dens interval or clivus-posterior odontoid process distance (P = .05). Measurement of neural canal width is a better predictor o...