Magnetic resonance imaging investigation of the atlanto-axial interspace.

The objective of this study is to examine the anatomy of the atlanto-axial interspace using magnetic resonance (MR) imaging. Two hundred and forty MR images of living subjects were examined for the presence of a posterior dural prominence and oblique hypointense fibers between the first and second cervical neural arches. Of the 240 images analyzed, 64% revealed a posterior concavity of the cervical dura mater. Of this, 24% also revealed oblique, linear hypointense fibers that appeared to be in direct contact with the dura mater. Twenty-three percent of the 240 images revealed oblique, linear hypointense fibers. Of the 23% that exhibited these fibers, 76% had an associated posterior thecal concavity of the cervical dura mater. A posterior dural prominence and oblique hypointense fibers were present in the atlanto-axial interspace in a significant number of randomly selected magnetic resonance images. These findings may represent normal, nonpathological anatomy found on MR images and may be related to a recently reported anatomical structure.