• Carlos A Rojas, Alex Hayes, John Christopher Bertozzi, Chantal Guidi, and Carlos Rodrigo Martinez.
• Department of Radiology, University of South Florida, Tampa, FL 33612, USA. crojas@health.usf.edu
• AJR Am J Roentgenol. 2009 Nov 1; 193 (5): 1388-92.

ObjectiveWe aimed to establish normal values on MDCT images for the atlantoaxial relationships including the atlantoaxial interval and lateral atlantodens interval (ADI) that could be used to detect atlantoaxial ligamentous injuries in adults and children.Materials And MethodsOne hundred seventy-eight healthy adult patients between 20 and 40 years old and 112 pediatric patients between 2 months and 10 years old underwent cervical spine MDCT with multiplanar reconstructions. The width of the joint space between the lateral mass of C1 and the lateral mass of C2 was measured at three equidistant points on both the left and right sides on coronal reformatted images to determine the atlantoaxial interval. The distance between the lateral surface of the dens and the medial surface of the lateral mass of C1 was measured in the coronal plane to determine the lateral ADI bilaterally.ResultsThe upper limit of the normal range of values for the atlantoaxial interval in adults was 3.34 mm on the right and 3.39 mm on the left. The upper limit of normal for the lateral ADI was 4.67 mm on the right and 5.6 mm on the left. More than 95% of the pediatric population was found to have an atlantoaxial interval of less than 3.9 mm on either side, a right lateral ADI of less than 7.4 mm, and a left lateral ADI of less than 8.0 mm.ConclusionWe propose that the obtained normal values be considered as the upper limits of the normal range for the atlantoaxial interval in adult and pediatric populations on MDCT images.

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