The intervertebral disc space is a cartilaginous joint with a central nucleus pulposus surrounded by an annulus fibrosus. Degenerative change in the nucleus pulposus is termed inter-vertebral osteochondrosis (Fig. 6-49A,B). Early signs of disc disease may include loss of fluid signal within the nucleus pulposus (dehydration), which results in decreased signal within the central portion of the disc on T2-weighted images, and blurring of the transition between the nucleus pulposus and the annulus fibrosus. This is followed later by narrowing of the intervertebral disc, which sometimes results in vertebral body end-plate degenerative changes. These end-plate changes are referred to as Modic changes (58). Modic type I changes are characterized by signal of edema, that is decreased signal on T1-weighted images and increased signal on T2-weighted images. Type II changes (Fig. 6-50A,B) follow the signal characteristic of fat, with intermediate to increased signal on T1-weighted images and increased signal on T2-weighted images. This is the most common type of reactive end-plate changes appreciated on degenerative osteochondrosis. Type III changes represent osseous sclerosis, characterized by decreased signal on both the T1- and the T2-weighted images.
FIGURE 6-49. A: Sagittal T2WI of the lumbar spine demonstrating different stages of intervertebral osteochondrosis. Normal disk (ND) demonstrates increased signal to the nucleus pulposus and normal height. With early degeneration (ED), the nucleus pulposus loses signal in part related to the decreased water content of the intervertebral disc but preserves the intervertebral height. With advanced degeneration (AD), there is near complete loss to the normal signal of the intervertebral disk and early traction osteophyte formation (TO). Note herniated disk (DH) at the L5-S1 segment. B: Advanced degenerative osteochondrosis on a different patient. There is loss of the intervertebral disk height, Schmorl’s node formation (SN) representing end-plate herniation and moderate traction osteophyte formation (arrow).
FIGURE 6-50. Sagittal T1- (A) and T2- (B) weighted images with degenerative osteochondrosis of the cervical spine. There is decreased T2 signal to most intervertebral discs, decreased disc height throughout, annular bulge, and traction osteophytosis. Note increased signal to the inferior end plate of C5 both on the T1- and T2-weighted images (arrows) characteristic of Modic type II changes.
When the disc becomes degenerated, it may undergo tearing of the annulus fibrosus collagen bundles, which is often a precursor to herniation of the nucleus pulposus, particularly at the posterolateral aspect of the disc. Protrusion is herniation of the nucleus pulposus that is contained by the annulus. In the axial plane, it usually demonstrates a base broader than the height against the parent disc (59). Extrusion is defined as a herniation of the nucleus pulposus beyond the fibers of the
The loss of the load-diffusing function of the normal disc also causes facet joint osteoarthrosis and marginal osteophytosis of the vertebral body ends (spondylosis deformans) by virtue of the increased loads these joints must bear.