Disk Protrusion/Herniation

      Any radial tear of the anulus is a potential site for herniation of the nucleus pulposus. On the sagittal view, dissection of nucleus pulposus through radial tears of the anulus is clearly depicted. Defects in the anulus with disk extending posteriorly are indicative of protrusion/herniation. In the sagittal plane, a herniated disk has an hourglass appearance along the posterior disk margin, which is described as a "squeezed toothpaste" effect. Axial scans show either asymmetry of the posterior disk margin or a soft-tissue mass displacing adjacent intraspinal structures.

      Most disk herniations occur in a posterolateral direction into the spinal canal because the tough posterior longitudinal ligament is thicker and tougher in the middle and resists posterior extension near the midline. A herniated disk usually impinges on the nerve root as it courses inferiorly toward the foramen at the next lower level. For example, an L4-L5 herniated disk impinges on the L5 root. The L4 root is likely unaffected unless there is lateral and cephalad migration of a free fragment into the neural foramen.

      The neural foramina are visualized on parasagittal images of the lumbar spine, and disk herniation can be detected by obliteration of foraminal fat. Nevertheless, axial MR is better for visualizing lateral disk herniations. Lateral disks compress the nerve root within the foramen or just beyond its lateral margin distal to the nerve root sheath.

      In the lumbar region, Ross's group found marked enhancement, distinct from epidural venous plexus, surrounding disk herniations. Histology disclosed peridiskal scar tissue similar to the epidural scar observed in postoperative patients. The depth of penetration of the scar depends on how long the disk fragment has been in the epidural space. The vascular scar tissue is a part of the body's repair mechanism to resorb and remove the offending disk material. Over time, the entire disk fragment may be resorbed. 

{To return to cases, use the "Back " button on the Toolbar}