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Nomenclature and Classification of Lumbar Disc Pathology


RECOMMENDATIONS

These recommendations present diagnostic categories and subcategories, intended for classification and the reporting of imaging studies. The terminology used throughout these recommended categories and subcategories remains consistent with detailed explanations given in the Discussion and with the preferred definitions presented in the Glossary.

The diagnostic categories are based upon pathology. Each lumbar disc can be classified in terms of one, and occasionally more than one, of the following diagnostic categories: Normal; Congenital/Developmental Variation; Degenerative/Traumatic; Infectious/Inflammatory; Neoplastic; and/or Morphologic Variant of Uncertain Significance (Figure 1). Each diagnostic category can be subcategorized to various degrees of specificity according to the information available and purpose to be served. The data available for categorization may lead the reporter to characterize the interpretation as "possible," "probable," or "definite."

Normal: Normal defines young discs which are morphologically normal, without consideration of the clinical context and not inclusive of degenerative, developmental, or adaptive changes that could, in some contexts (e.g. normal aging, scoliosis, spondylolisthesis) be considered clinically normal. However, the bilocular appearance of the adult nucleus resulting from the development of a central horizontal band of fibrous tissue is considered a sign of normal maturation.

Congenital/Developmental Variation: The Congenital/Developmental Variation category includes discs that are congenitally abnormal or that have undergone changes in their morphology as an adaptation to abnormal growth of the spine such as from scoliosis or spondylolisthesis.

Degenerative/Traumatic: Degenerative and/or traumatic changes in the disc are included in a broad category that includes subcategories of: Anular Tear; Herniation; and Degeneration. Characterization of this group of discs as Degenerative/Traumatic does not imply that trauma is necessarily a factor or that degenerative changes are necessarily pathologic as opposed to the normal aging process.

Anular tears, also properly called anular fissures, are separations between anular fibers, avulsion of fibers from their vertebral body insertions, or breaks through fibers that extend radially, transversely, or concentrically, involving one or many layers of the anular lamellae. The terms "tear" or "fissure" describe the spectrum of such lesions and do not imply that the lesion is consequent to trauma. (Figure 2)

Degeneration may include any or all of: real or apparent desiccation, fibrosis, narrowing of the disc space, diffuse bulging of the anulus beyond the disc space, extensive fissuring (i.e. numerous anular tears) and mucinous degeneration of the anulus, defects and sclerosis of the end-plates, and osteophytes at the vertebral apophyses. A disc demonstrating one or more of these degenerative changes can be further qualified into two sub-categories: spondylosis deformans, possibly representing changes in the disc associated with a normal aging process; or intervertebral osteochondrosis, possibly the consequences of a more clearly pathologic process (Figure 3).

Herniation is defined as a localized displacement of disc material beyond the limits of the intervertebral disc space (Figure 2). The disc material may be nucleus, cartilage, fragmented apophyseal bone, anular tissue, or any combination thereof. The disc space is defined, craniad and caudad, by the vertebral body end-plates (Figure 4) and, peripherally, by the outer edges of the vertebral ring apophyses, exclusive of osteophytic formations (Figure 5). The term "localized" contrasts to "generalized," the latter being arbitrarily defined as greater than 50% (180 degrees) of the periphery of the disc (Figure 6).

Localized displacement in the axial (horizontal) plane can be "focal," signifying less than 25% of the disc circumference (Figure 7), or "broad-based," meaning between 25 and 50% of the disc circumference (Figure 8). Presence of disc tissue "circumferentially" (50-100%) beyond the edges of the ring apophyses may be called "bulging" and is not considered a form of herniation (Figure 9), nor are diffuse adaptive alterations of disc contour secondary to adjacent deformity as may be present in severe scoliosis or spondylolisthesis (Figure 10).

Herniated discs may take the form of protrusion or extrusion, based on the shape of the displaced material (Figure 11). Protrusion is present, if the greatest distance, in any plane, between the edges of the disc material beyond 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 disc material at the outer margin of the disc space of origin, where disc material displaced beyond the disc space is continuous with disc material within the disc space. In the cranio-caudal direction, the length of the base cannot exceed, by definition, the height of the intervertebral space. Extrusion is present when, in at least one plane, any one distance between the edges of the disc material beyond the disc space is greater than the distance between the edges of the base in the same plane, or when no continuity exists between the disc material beyond the disc space and that within the disc space (Figure 12). Extrusion may be further specified as sequestration, if the displaced disc material has lost completely any continuity with the parent disc (Figure 13). The term migration may be used to signify displacement of disc material away from the site of extrusion, regardless of whether sequestrated or not (Figure 14). Because posteriorly displaced disc material is often constrained by the posterior longitudinal ligament, images may portray a disc displacement as a protrusion on axial sections and an extrusion on sagittal sections, in which cases the displacement should be considered an extrusion. Herniated discs in the cranio-caudal (vertical) direction through a break in the vertebral body end-plate are referred to as intravertebral herniations.

Disc herniations may be further specifically described as contained, if the displaced portion is covered by outer anulus, or uncontained when absent any such covering. Displaced disc tissues may also be described by location, volume, and content, as discussed later in this document. Figure 15 lists the proposed categories for description and classification of disc herniations.

Inflammation/Infection: The category of Inflammation/Infection includes infection, infection-like inflammatory discitis, and inflammatory response to spondyloarthropathy. It also includes inflammatory spondylitis of subchondral endplate and bone marrow manifested as Modic Type 1 MRI changes and usually associated with pathologic changes in the disc. To simplify the classification scheme, the category is inclusive of disparate conditions; therefore, when data permit, the diagnosis should be subcategorized for appropriate specificity.

Neoplasia: Primary or metastatic morphologic changes of disc tissues caused by neoplasia are categorized as Neoplasia, with sub-categorization for appropriate specificity.

Morphologic Variant of Unknown Significance: Instances in which data suggest abnormal morphology of the disc but are not complete enough to warrant a diagnostic categorization can be categorized as Morphologic Variant of Unknown Significance.


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Introduction
Preface Introduction Recommendations Discussion (part 1)
Discussion (part 2) Glossary References Appendix

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Copyright 2001 Lippincott, Williams & Wilkins
Presented by American Society of Neuroradiology, American Society of Spine Radiology

and North American Spine Society