Degenerative Disc Disease

General characteristics

In 2001, the Combined Task Forces of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology proposed a new nomenclature and consistent classifi cation system, intended for the reporting of imaging studies (Fardon and Milette 2001; Milette 2001).

The general classifi cation of disc lesions is given in Table 1 (Milette 2000).

  • Normal (excluding aging changes)
  • Congenital/developmental variant
  • Degenerative/traumatic lesion
    • Anular tear
    • Herniation
      • Protrusion/extrusion
      • Intravertebral
    • Degeneration
      • Spondylosis deformans
      • Intervertebral osteochondrosis
  • Infl ammation/infection
  • Neoplasia
  • Morphologic variant of unknown signifi cance

Other classifi cation systems in use which are based on the three-joint complex: the intervertebral disc (anterior column of the spine) and the two facet joints (posterior column) (Thalgott et al. 2004). In this chapter, we shall follow the general classifi cation of disc lesions as proposed by the Combined Task Forces.

MRI Characteristics

  • Signal loss on T2-weighted scans
  • Loss of height of the intervertebral disc
  • Other signs
  • Annular Tears
  • Herniation
  • Schmorl’s nodes
  • limbus vertebra
  • Bulging

Signal loss on T2-weighted scans

Signal loss on T2-weighted scans is an early indicator of intervertebral disc degeneration on MRI (Modic and Herfkens 1990; Sether et al. 1990). The decrease in signal intensity is caused by the increase in fi brous tissue (collagen), which replaces the mucoid matrix of the nucleus pulposus. In the process of normal aging, the decrease in central disc signal intensity on T2-weighted MRI scans should be uniformly distributed among all the discs of the individual.

degeneratika_hryaschya

Fig.

In the lumbar spine L5–S1 and L4–L5 are most commonly affected. In the cervical spine, the C5–C6 and C6–C7 discs are most frequently involved (these segments bear the brunt of cervical spine motion).

stadii_degeneracii_disca

Fig.

Loss of height of the intervertebral disc

Loss of height of the intervertebral disc is the earliest sign of disc degeneration to be seen on plain X-ray films. When assessing disc height, the position of the patient (standing or lying down) during the examination should be taken into account.

Other signs

Other signs, such as osteochondrotic changes, including sclerosis of the vertebral endplates with osteophytes, calcifi cation and the vacuum disc phenomenon, are more reliable, though they indicate secondary or late stages of degenerative changes (Resnick 1985).

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petrifikat_disca

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Annular Tears

The intervertebral disc becomes less elastic and more fi brous. Eventually this leads to the formation of cracks and fi ssures in the annulus fi brosus, which are known as “annular tears”. Annular tears can be classifi ed as concentric, transverse or radial (Osti et al. 1992).

Herniation

Herniation is defi ned as a localized displacement of disc material (nucleus, cartilage, fragmented apophyseal bone, fragmented annular tissue) beyond the limits of the intervertebral disc space (Fardon and Milette 2001).

hernia_intervertebral_disc

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hernia_ct

Fig.

Schmorl’s nodes

Herniated discs in the cranio-caudal (vertical) direction through a break in one or both of the vertebral body endplates are referred to as “intravertebral herniations” (also known as Schmorl’s nodes). They are often surrounded by reactive bone marrow changes.

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limbus vertebra

In young individuals, intrabody herniation of disc material can instigate the formation of a “limbus vertebra”. When herniation of the nucleus pulposus occurs through the ring apophysis prior to bony fusion, a small segment of the vertebral rim may become isolated (Mupparapu et al. 2002). Limbus vertebrae are most commonly found in the midlumbar region, and less commonly in the mid-cervical region. They are characterized by a defect in the anterior margin of the vertebral body usually at the anterior superior margin in the lumbar spine, and the anterior inferior margin in the cervical spine.

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Bulging

Generalized or circumferential disc displacement (involving 50% to 100% of the disc circumference) is known as “bulging”, and is not considered a form of herniation. Bulging can be symmetrical (displacement of disc material is equal in all directions) or asymmetrical (frequently associated with scoliosis).

degeneratika_mp_disca

Fig.