Effect of degeneration of the intervertebral disk on the process of diffusion.

PURPOSE To test the hypothesis that diffusion of contrast medium into the intervertebral disk is affected by the integrity of the nucleus pulposus and annulus fibrosus. METHODS In canine intervertebral disks, defects were made in the annulus fibrosus and nuclear material was removed from the disk with a nucleotome. MR imaging was performed with intravenous contrast medium at 15, 30, 60, and 90 days after the procedure. The diffusion of contrast medium in the intervertebral disk was studied by visual inspection and by measuring changes in signal intensity. The intervertebral disk were classified at each MR study as normal or abnormal on the basis of the signal intensity on T2-weighted images. RESULTS In untreated disks after intravenous injection of contrast medium, a band of increased signal intensity was observed near the endplates that became wider with time and approached the center of the disk. In six of the 12 treated disks, the band of increased signal intensity was visibly diminished or less discrete compared with that in the control disks. Weeks later, these treated disks showed diminished signal intensity on T2-weighted images and bulging of the annulus fibrosus. CONCLUSIONS Intervertebral disks with defects in the annulus fibrosus and reduced cartilage content were characterized by abnormal diffusion of contrast medium into the disk, and changes characteristic of early disk degeneration were detected subsequently.