Comparación entre los métodos y herramientas para la planificación

are generally well tolerated, the disk can demonstrate apparently similar degenerative changes at an earlier-than-expected age that, because of their premature character and location, can be pathologic.

There are strong analogies, but not complete similari-ties, between the aberrations of the aged disk and those of a degenerated disk in a young patient. In the aging process, the rate of mucopolysaccharide production increases for a short time around age 40 and then returns to a rate equal or slightly inferior to that at its starting point. On the other hand, in cases of herniated disks, the decline in mucopolysaccharide production is rapid, significant, and progressive. In patients 20 years of age, one can already notice slight localized degeneration of fibers in the deep layers of the annulus, most often pos-teriorly. Gradually, their number and size increase and form (about at age 40) small fissures in the laminae. By age 30, these areas become susceptible to injury by tearing or enlarged by pressure on the nucleus. There are two types of rupture of the annulus: radial tears and concentric splits or tears. The latter form cracks in the shape of arches parallel to the laminae, localized usually to the lateral and anterior parts of the disk.

The radial tears start at the contact region between the nucleus pulposus and the annulus fibrosus and extend to the periphery. They are predominant in the posterior or posterolateral aspect of the disk. They are of variable size, narrow or wide, and generally unique; there may be two or three (de Séze).

When the tears are wide, segments of the nucleus pul-posus can protrude into them. If a fragment goes toward the front or the sides, there will be no pain, but it will lead to the formation of osteophytes. On the other hand, frag-ments extending posteriorly will bulge and contact the superficial annular fibers. The distention of these fibers and the forceful or strenuous pressure exerted simulta-neously on the posterior longitudinal ligament will cause pain of the acute lumbar disk type. Finally, frank rupture of the superficial annular fibers may occur, resulting in extrusion of the nucleus pulposus. This is known as a noncontained herniated disk (Fig. 15.1).

The substance of the nucleus pulposus can also infil-trate through a tear in the annulus fibrosus. This is the mechanism of painful internal disk disruption. Finally, the posterior superficial laminae distended under the influence of postural forces or exertion effort can be sources of chronic lumbar disk pain.

The production of pain need not be solely a mechanical phenomenon. Soft tissue injury can produce many types of substances with algogenic potential. For example, the rupture of a herniated disk has been shown to provoke the liberation of a primary mediator of the inflammatory cas-cade, phospholipase A₂, which acts as the rate-limiting step in the production of prostaglandins and leukotrienes (J.S. Saal, R.C. Franson, R. Dobrow, J.A. Saal, A.H.

White, and N. Goldthwaite).

Herniated Disks

A posteriorly herniated disk can come into contact with a nerve root, compress it, irritate it, and cause inflamma-tion, which is the primary source of pain. This is the usual mechanism of the common femoral neuralgia and sciatica.

At the cervical level, foraminal stenosis due to osteo-phyte formation (de Séze) is most often the cause for the cervicobrachial neuralgia. The protrusion of a fragment of the nucleus, generally after excessive activities, is very rarely the cause.

84 SECTION III PAIN OF SPINAL ORIGIN

Herniated disks are most frequent at the lumbar level.

In statistics cited by the Clinique Universitaire de Neuro-chirurgie de Zurich on 2941 cases, there were:

• 1098 herniations of the L5–S1 disk

• 1667 herniations of the L4–L5 disk

• 135 herniations of the L3–L4 disk

• 14 herniations of the L2–L3 disk

• 7 at the level of the inferior dorsal spine

• 20 at the level of the last cervical disks At Lumbar Level

The herniations are most often posterolateral, as the posterior longitudinal ligament reinforces the interverte-bral disk posteriorly. Some herniations remain subliga-mentous, but others break through this ligament (Fig. 15.3).

Posterolateral herniation— This is the most frequent type of herniated disk often leading to compression or irritation of the corresponding spinal root (Fig. 15.1 and Fig. 15.2). It can compress the nerve root from either a lateral or medial side. It can also compress the root of the subjacent level superiorly or extend inferiorly via a sequestered fragment. It is then said to be in superior or inferior sublaminar position.

Posterior herniation — This type of herniation can deform the posterior longitudinal ligament and compress the dural sac without irritating the nerve roots. It can be responsible for chronic lumbar pain with acute exacerba-tions or for subacute lumbar pain with lumbar stiffness (Fig. 15.2).

Transligamentous herniation — Among the hernia-tions (sometimes small) that have broken the posterior longitudinal ligament, some remain in continuity with the disk while others are separated into multiple sequestered fragments that pose difficulty for surgical dissection.

These free fragments can be visualized on magnetic res-onance imaging (MRI) and in certain cases, with sacrora-diculography.

Discography may also be useful in demonstrating the existence of an anterior or lateral herniation. Classically, these types of herniations are asymptomatic. Schmorl’s nodules are also forms of herniation into the vertebral body. These lesions can contribute to some instability of the segment (see Chapter 17, “Painful Minor Interverte-bral Dysfunctions”).

At Thoracic Level

Disk herniations are rare in this region. They produce thoracic pain or pain referred to the pelvic region and the legs. Often, they are accompanied by nocturnal paresthe-sias (hyperesthesia, burning pains, stiffness). The motor deficit can range from a simple impression of weakness in one leg to total paraplegia. MRI is the imaging study of choice to detect these herniations.

At Cervical Level

At the cervical spine level, there are hard herniations formed by the disco-osteophytic nodule, a spondylotic reaction at the level of an uncinate process, and the true

Figure 15.1 Horizontal flexion. Left. Posterolateral herniated disk with compression of the nerve root. Right. Median disk herniation compromising the dural sac and cauda equina. a. Normal disk. b. Bulging disk due merely to an outward bulging of the superficial fibers of the annulus fibrosus that are not broken. c. Herniated disk with the superficial fibers of the annulus fibrosus ruptured and the nucleus pulposus able to gain exit and compromise the spinal nerve.

CHAPTER 15 VERTEBRAL LESIONS AND COMMON PAIN SYNDROMES 85

herniated disks called soft herniations that are much rarer.

These can be:

• Posterolateral, compromising the spinal nerve (Fig. 15.4, 1)

• Intraforaminal, threatening the spinal nerve also (Fig. 15.4, 3)

• Much more rarely, posterior and median, threaten-ing the dura mater, spinal cord, and anterior spinal artery (Fig. 15.4, 2)

MRI or computed tomography (CT) scanning after injection of myelographic contrast can be of help in iden-tifying them.

Figure 15.2 Transverse section showing different modes of compression by a herniated disk. a. Normal state. b. Simple protrusion. c. Posterolateral disk herniation. d. Posterior disk herniation.

Figure 15.3 Different types of herniated disks (according to Junghanns). a. Without rupture of posterior longitudinal ligament.

b. With rupture of posterior longitudinal ligament. c. Disk extrusion beneath posterior longitudinal ligament. d. Sequestered fragment.

86 SECTION III PAIN OF SPINAL ORIGIN

Intervertebral discs may also be subject to annular tears which in some cases may be painful with or without local nerve compression.

Pain related to annular disc tear may have painful fea-tures related to local segmental sensitization reflected by presentations typical of segmental cellulotenoperi-osteomyalgic syndrome.