Computerized tomography in persons with Down syndrome and atlantoaxial instability.

Atlantoaxial instability has been reported to occur in 9-31% of persons with Down syndrome. The authors studied a subsample of patients with this chromosomal disorder who had both routine roentgenograms and computerized tomographic examinations. Computerized tomography revealed numerous skeletal anomalies of the C1-C2 region as well as spinal cord compression that were not visualized on plain roentgenograms. In addition, an apparent discrepancy of the atlanto-dens interval measurements between the two procedures was noted. The measurements of the plain roentgenograms were significantly greater than those obtained by computerized tomography, which is due to the magnification factor in plain roentgenograms.