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AJNR - American Journal of Neuroradiology

Published ahead of print on September 24, 2007
doi: 10.3174/ajnr.A0660

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Reassessment of the Craniocervical Junction: Normal Values on CT

C.A. Rojas^a, J.C. Bertozzi^a, C.R. Martinez^a and J. Whitlow^a

^a From the University of South Florida College of Medicine, Tampa, Fla

View larger version (87K): [in this window] [in a new window]   Fig 1. BAI. Midsagittal MDCT image of the craniocervical junction demonstrates the posterior axial line drawn along the posterior cortex of the body of the axis and extended cranially. The BAI is the distance between the basion and this line.

View larger version (85K): [in this window] [in a new window]   Fig 2. Midsagittal MDCT image of the craniocervical junction demonstrates the BDI as the distance from the most inferior portion of the basion to the closest point of the superior aspect of the dens.

View larger version (87K): [in this window] [in a new window]   Fig 3. Midsagittal MDCT image of the craniocervical junction demonstrates the Powers ratio, which is calculated by dividing the distance between the tip of the basion to the spinolaminar line by the distance from the tip of the opisthion to the midpoint of the posterior aspect of the anterior arch of C1.

View larger version (85K): [in this window] [in a new window]   Fig 4. Midsagittal MDCT image of the craniocervical junction demonstrates the ADI, which is calculated by drawing a line from the posterior aspect of the anterior arch of C1 to the most anterior aspect of the dens at the midpoint of the thickness of the arch in craniocaudal dimension.

View larger version (84K): [in this window] [in a new window]   Fig 5. Sagittal MDCT image of the craniocervical junction demonstrates the AOI, which is calculated by drawing a line perpendicular to the articular surfaces of the occipital condyle and the lateral mass of C1. This line is drawn at the center of the articulation by correlating the sagittal and coronal images.

View larger version (48K): [in this window] [in a new window]   Fig 6. Interexaminer variability of the BAI. Midsagittal MDCT image of the craniocervical junction demonstrates the posterior axial line (PAL) drawn along the posterior cortex of the body of the axis and extended cranially. A, Examiner A draws the PAL on the basis of a single interpretation of the posterior cortex of the body of the axis. B, Examiner B draws the PAL using a different interpretation of the posterior cortex of the body of the axis.