The lateral atlanto-dens interval: normal range of asymmetry
Purpose: The object of this study is to determine the normal range of asymmetry of the lateral atlanto-dens interval (LADI). Methods: Ninety-nine consecutive patients who had CT scans of the atlanto-axial complex for reasons unrelated to the upper cervical spine were studied. Subjects with a history of cervical trauma or rheumatoid arthritis were excluded. The LADI was measured at a workstation using an electronic cursor. The difference in the LADI between the right and the left side was taken as the measure of asymmetry. Results: The average asymmetry of the LADI was 0.99 ± 1.05 mm. While a number of subjects had symmetrical LADI, the maximum asymmetry in this study population was 5 mm. Conclusion: Asymmetry of the LADI is not unusual in subjects with no symptoms referable to the upper cervical spine. The LADI as a measurement in itself does not signify any type of clinical pathology. The average asymmetry at the middle third of the dens is approximately 1 mm. Ninety-five percent of patients will have an asymmetry of 3 mm or less. The LADI asymmetry is best determined in a CT section that demonstrates the maximal width of the dens. Radiologists and clinicians should be aware of this normal range of asymmetry when interpreting CT scans of the atlanto-axial region.
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