Computed tomography in the diagnosis of a herniated disk at the L5-S1 level.

Six patients with a normal myelogram were found to have evidence of a herniated nucleus pulposus (HNP) at the L5-S1 level on computed tomography (CT) scan. In all six patients, the presence of the herniated disk was confirmed at surgery. Five of the six herniations were lateral. The authors found no patients with an abnormal myelogram and a normal CT at the L5-S1 level in a technically good study. The sensitivity of the CT in diagnosing an HNP at the L5-S1 interspace is greater than with myelography if images in the exact plane of the disk can be obtained.