Computed tomographic appearance of the bulging annulus.

Criteria have not been established for differentiating herniated nucleus pulposus and bulging annulus fibrosus by computed tomography (CT). The CT diagnosis of a bulging annulus was evaluated by correlating the CT and anatomic appearance of cadaver lumbar spines, and by comparing CT and surgical findings in patients undergoing lumbar laminectomy. We found that in anatomically or surgically verified bulging annulus, CT showed generalized extension of the disk margin beyond the vertebral body margins. Therefore, bulging annulus can be distinguished by CT from herniated nucleus, which has a focal, usually posterolateral, protrusion of the disk margin.