Magnetic resonance imaging of the normal craniovertebral junction.

Sagittal magnetic resonance images of the normal craniovertebral junction in 25 patients were examined for visualization of bony, synovial, and ligamentous structures. The excellent delineation of soft tissue by magnetic resonance imaging enabled recognition of the joint space between the dens and anterior arch of C1 in 14 out of 25 patients. High-signal-intensity tissue was noted immediately superior to the dens in all patients; an anatomic specimen confirmed the fibrofatty nature of this tissue. The medullary space of the dens had lower signal intensity than did the marrow in the body of C2 in more than one half of the cases. Additional thin-section images suggested that this was a partial-volume artifact. Understanding of the normal appearances of structures in this region is necessary to assess correctly the presence or absence of disease.