THE HISTOLOGY OF LUMBAR INTERVERTEBRAL DISC HERNIATION - THE SIGNIFICANCE OF SMALL BLOOD-VESSELS IN THE EXTRUDED TISSUE

Six hundred surgical cases of lumbar intervertebral disc herniation were evaluated histologically for the presence of blood vessels. These patients ranged in age from 12 to 77 years. Blood vessels were observed in 57 of 101 cases of complete prolapse type of herniated disc (56.4%), 12 of 32 cases of incomplete prolapse type of herniated disc (37.5%), and 53 of 467 cases of protrusion type of intervertebral disc herniation (11.3%). The presence of blood vessels in intervertebral discs was also investigated in postmortem specimens. Blood vessels were observed in 293 of 616 intervertebral discs (T10-L5), in individuals older than 40 years of age from 100 postmortem spines. The specimen age range was 16-89 years. Most of the blood vessels seen in the extruded tissue, exposed to the epidural space in cases of complete and incomplete prolapse type of herniation, are thought to have been newly formed after herniation occurred. As invasion of the intervertebral disc by blood vessels was found to occur with the advance of age, it is possible that such blood vessels become extruded with the intervertebral disc tissue. The intervertebral disc may herniate posteriorly in three basic patterns. The first pattern is ''protrusion type of herniated disc.'' In protrusion hernia type there is abnormal posterior bulging of the anulus fibrosus. The disc pathology is predominantly nucleus pulposus, and the peripheral layer of the anulus fibrosus remains attached to the vertebral body bony rim, however. In the second pattern, ''incomplete prolapse type of herniated disc,'' the peripheral anulus fibrosus has become detached from a portion of the vertebral body rim, exposing disc tissue to the epidural space. This tissue is still in continuity with the disc, however. There are no free fragments of disc tissue, and as such, this is considered an incomplete prolapse type of herniation. The third pattern is ''complete prolapse type of herniated disc,'' in which the peripheral anulus fibrosus has become detached from a portion of the posterior vertebral body rim, exposing disc tissue to the epidural space. In this pattern there is free disc tissue that is no longer in continuity with the disc. This is considered extruded tissue. Free specimens of extruded tissue, removed as independent pieces, are found during surgery for complete prolapse type of herniated disc. Frequently most of this tissue is composed of anulus fibrosus. Small blood vessels accompanied by loose fibrous tissue are sometimes observed in the marginal regions of these free extruded pieces of anulus. The origin of these small blood vessels is unclear. It is possible that pre-existing blood vessels within the intervertebral disc became extruded together with the herniated tissue, or that newly formed blood vessels after herniation occurred. But blood vessels are not usually observed in the intervertebral disc. If the origin of blood vessels was the intervertebral disc, then their presence with the extruded tissue would provide histologic evidence as to the origin of the herniation. Namely, there is an opinion that blood vessels in the extruded tissue of complete and incomplete prolapse type of herniations are thought to be characteristic of these patients of herniations, but this study has mentioned that blood vessels could be seen in protrusion type of herniated disc also, and blood vessels in the extruded tissue in cases of prolapse type of herniations are thought to have been extruded with the intervertebral disc tissue, to have newly formed after herniation occurred. This study has investigated the significance of these small blood vessels.