Pseudovacuum of the cervical intervertebral disc: a normal variant.

A lucency in the intervertebral disc space at the superior margin is a normal variant related to Mach band phenomenon. This may easily be confused with a true vacuum sign in intervertebral disc injury. Patients with the pseudovacuum have no associated radiographic findings to suggest injury about the suspected disc space. A review of a group of normal lateral cervical vertebral films showed the phenomenon to occur in 65% of adults and 50% in children.