Terminology and classification of lumbar disc pathology

Recommendations of the Joint Task Forces of the North American Spine Society, the American Society of Spine Radiology, and the American Society of Neuroradiology

These guidelines are diagnostic categories and subcategories designed to classify and interpret images. Each lumbar disc may be classified into one, and sometimes more than one, of the following diagnostic categories.

• Normal;
• Congenital/Developmental variant;
• Degenerative/Traumatic;
• Infectious/Inflammatory;
• Neoplastic;
• Morphological variant of indefinite meaning

Each diagnostic category can be divided into subcategories of varying degrees of specificity, according to the information available and the purpose of use. The information available for categorization may lead the researcher to use interpretations such as "possible," "probable," or "definite."

General classification of disc damage

• Normal (except for age-related changes)
• Congenital / developmental variant
• Degenerative/Traumatic Injury
• Ring tear
• Herniation
  • Protrusion / Extrusion
  • Intervertebral
• Degeneration
  • Deforming spondylosis
  • Intervertebral osteochondrosis
• Inflammation/infection
• Neoplasia (tumor)
• Morphological variant of unknown meaning

Normal

The definition of "normal" implies young discs that are morphologically normal, without consideration of the clinical context, and does not include degenerative, developmental, or adaptive changes that might in some cases (eg, normal aging, scoliosis, spondylolisthesis) be considered clinically normal.

Congenital / developmental variant

The congenital/developmental variation category refers to discs that are congenitally abnormal or have undergone a change in their morphology as an adaptation to abnormal growth of the spine, such as in scoliosis or spondylolisthesis.

Degenerative and/or traumatic injury

Degenerative and/or traumatic disc changes represent a broad category that is further divided into subcategories: annular rupture, herniation, and degeneration. Describing this group of disc pathologies as degenerative/traumatic does not imply that trauma must necessarily be a factor or that degenerative changes are necessarily pathological in nature, as opposed to the normal aging process.

Annular tears, also properly called annular fissures, are characterized by separations of the annular fibers, ruptures of fibers from their attachments to the vertebrae, or disruptions of fibers arranged radially, perpendicularly, or concentrically involving one or more layers. The terms "tear" or "fissure" do not imply that the injury is due to trauma.

Degeneration includes some or all of the following actual or suspected processes: dehydration, fibrosis, loss of disc height, diffuse protrusion of the annulus beyond the disc surface, multiple fissures (i.e., multiple tears in the annulus) and mucoid degeneration of the annulus, end plate defects and sclerosis, and osteophytes of the vertebral apophyses. A disc that exhibits one or more of these degenerative changes may be further classified into two subcategories: either spondylosis deformans, which usually represents disc changes associated with the normal aging process; or intervertebral osteochondrosis, which usually results from a more obvious pathological process.

Herniation is defined as a localized displacement of disc material beyond the intervertebral disc territory. The herniated material may be nucleus, cartilage, fragmented apophyseal bone, annular tissue, or any combination thereof. The disc space is limited cranially and caudally by the vertebral endplate and peripherally by the outer ends of the annular apophyses, excluding osteophytes. The term "localized" is contrasted with "generalized," where the latter is loosely defined as more than 50% (180 degrees) of the disc periphery.

Focal displacement in the horizontal plane may be "focal", occupying less than 25% of the disc circumference, or "extensive", occupying 25 to 50% of the disc circumference. The presence of disc tissue occupying 50% to 100% of the circumference beyond the margins of the annulus apophyses may be called "bulging" and is not considered either a form of herniation or diffuse adaptive changes in the disc contour with adjacent deformity, as may be seen in severe scoliosis or spondylolisthesis.

A herniated disc may take the form of a protrusion or an extrusion, determined by the shape of the displaced material. A protrusion occurs when the greater distance in any plane between the edges of the disc material outside the disc space is less than the distance between the edges of the base in the same plane. The base is defined as the cross-sectional area of the disc material of the outer margin of the original disc area where the disc material displaced outside the disc space is continuous with the disc material inside the disc space. In the craniocaudal direction, the length of the base cannot exceed, by definition, the height of the disc space. An extrusion occurs when, in at least one plane, any distance between the edges of the disc material outside the disc space is greater than the distance between the edges of the base, or when there is no continuity between the disc material outside the disc space and that inside the disc space.

Extrusion may be further defined more precisely as sequestration (sloughing of necrotic material from viable tissue) if the displaced disc material has completely lost its attachment to the parent disc. The term migration may be used to define movement of disc material away from the side of extrusion, whether or not it is sequestered. Given that the later displaced disc material is often trapped by the posterior longitudinal ligament, images may show disc movement as protrusion on an axial (longitudinal) view and as extrusion on a sagittal view, in both cases the movement should be considered an extrusion. Herniation of intervertebral discs in the craniocaudal (vertical) direction through a ruptured end plate of the vertebral body is referred to as intervertebral disc herniation.

A herniated disc may be described as retained (fixed) when the displaced portion is enclosed by the outer ring, or non-retained (non-fixed) when any such covering is absent. The tissues of the displaced disc may also be described by location, volume, and content.

Description of a herniated disc

• Morphology
  • Protrusion
  • Extrusion.
  • Into the vertebral body
• Retention
• Integrity
• Relationship with the posterior longitudinal ligament
• Volume
• Compound
• Localization