Condition affecting the spine, in which a tear in the outer, fibrous ring (annulus fibrosus) of an intervertebral disk allows the soft, central portion (nucleus pulposus) to bulge out. This tear in the disk ring may result in the pressurized contents striking and compressing the spinal cord, causing pain and/or paresis. The disease progresses when persistent compression damages neurons and blood vessels causing the release of inflammatory chemical mediators and decreasing blood flow to the spinal cord resulting in severe pain. Type I disk disease occurs with a total rupture of the dorsal part of the annulus and extrusion of the nucleus pulposus into the spinal canal. Type II disk disease occurs with a bulging of the annulus fibrosis into the spinal canal.