The New Nomenclature of the Spine

By Arthur Croft, DC, MS, MPH, FACO

In the pre-CT scan days of the 1970s, the only diagnostic tool available for diagnosing a space-occupying disc lesion was myelography. Life was simple (unless, of course, you were on the receiving end of such a procedure).

Many of us were taught back in those days that discs themselves were insensitive, having no nerve supply. Then things began to get complicated. Around the same time that the CT scanners began to appear in teaching hospitals, histologists and anatomists began to report finding sensory nerves in discs. Initially, these were thought to be only part of a pathological process, perhaps secondary to degeneration or trauma, but eventually, newer staining techniques demonstrated that even healthy discs had not only sensory nerves, but also mechanoreceptors.¹ Indeed, pain can be evoked even in healthy discs using discography, which complicated the picture quite a bit. It meant that the disc could now be a problem, not just because it was compressing some neural structure, but in other capacities as well. Thus, not all discopathies involve herniations, although it appears some clinicians have not noticed, which is another story.

Meanwhile, with the advent of new hardware scanning technologies, coupled with higher resolution imaging and technically capable software, a new nomenclature has necessarily evolved to allow clinicians to extend their repertoire of diagnostic terminology. Along the way, however, as with any nascent field of science, some of the early terminology has been cashiered for a clearer or more precise phraseology. Unfortunately, many clinicians continue to rely on older terms. In many cases, no serious harm is done by using outdated terms, if most physicians are familiar with the language, but, as I always remind my students, it is just as easy to use the correct terminology and avoid appearing terminologically déclassé.

Impelled by the growing lexicon of disc terminology and lack of any real consensus in the scientific and clinical communities, the North American Spine Society (NASS) called for a convocation of a nomenclature development group or task force consisting of itself, the American Society of Spine Radiology (ASSR), and the American Society of Neuroradiology (ASNR). The resulting document, which is the subject of this brief review, was endorsed by all three organizations, as well as by the Joint Section on Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons (AANS) and Congress of Neurological Surgeons (CNS), and the CPT and ICD Coding Committee of the American Academy of Orthopaedic Surgeons (AAOS). With the endorsement of such lofty assembly, suffice it to say this is a lexicon you can rely on. Readers also should understand that although the title of the paper refers to the lumbar spine, this nomenclature also is intended to apply, to the extent possible, to the cervical and thoracic spines.²

The paper contains a large glossary of terms that I will not reproduce here and I heartily recommend this paper as an important reference to keep handy. Of the more commonly used (and sometimes misused) terms, I will mention several here. In several cases, I have created illustrations that are similar to the originals to facilitate understanding. I must confess that I found some of the definitions a bit perplexing, requiring several re-reads to understand.

In any case, the authors describe two forms of degeneration: spondylosis deformans(spondylosis is a shortened form and is commonly used synonymously) and intervertebral osteochondrosis. The former is largely a specialized category of "degeneration" which exists as an early process affecting the anulus and some marginal osteophytes, resulting in only minimal disc height loss if any. The latter term is reserved for a more advanced pathological state in which disc, end plate, and nucleus are affected and there is disc space narrowing with possible vacuum phenomena and vertebral body reactive changes. And, before we go any further, anulus is spelled with one "n" and disc with a "c." Also, it is "end plate" unless used as an adjective, at which point it is hyphenated. So, one must have a fractured end plate or an end-plate fracture.

Even in the world of computers, they have disc problems, it seems. In the electronic world, diskrefers to magnetic media, while disc refers to optical media, such as a CD-ROM. In the medical world, Dorland's has after disc, disk. But the root is the Latin discus. Under disk, there is much more terminology, and this derives from the Greek diskos. Intervertebral disk is here. Note that MEDLINE's MeSH uses disk, even though many now use disc. Andy Rooney might want a piece of this action!

Bulging of the disc is a common term and connotes less than 3 mm of extension beyond the normal margin. One can have symmetrical bulging, in which the entire 360 degrees of disc is bulging, or asymmetrical bulging, in which one side bulges while the other does not.

There have been many terms used in the description of herniation, and illuminating just this one area probably would have been a worthy capstone for the above-mentioned nomenclature committee, and a sufficient reason to swear allegiance to the new lexicon. So, here are the common terms used today and the committee's views on them. We have herniated nucleus pulposus (HNP), which is discouraged now because bone, anulus and other components also can be herniated;ruptured disc, which is discouraged because it implies great trauma;prolapsed disc, which is not commonly used and is simply not recommended by the committee; and finally, if one is gifted with even greater astucity or diagnostic information (probably both), one could diagnose a protruded disc, which represents a herniation in which the distance of protrusion is less than the width of the base (a metric equivalent to the vertical height of the disc at the posterior aspect), or an extruded disc, in which the distance of protrusion exceeds the width of the base. The fundamental unit of this verbal currency is herniated disc.

When extrusion is complete, the disc is sequestered and the free fragment or sequestrum might be said to have migrated, if such were the case. A disc also can be contained or uncontained, depending on whether there is any open channel from the nucleus to the exterior. Of course, without a discogram, this would not be known with any certainty. In terms of the herniation's position relative to the posterior longitudinal ligament (PLL), it may further be described as'subligamentous, if it has not breached the PLL, or extraligamentous, transligamentous or perforated if it has.

Quite often, radiologists describe protrusions or bulges in terms of mm distances, which can create problems in interpretation because of magnification errors in imaging and because the degree to which a given herniation is relevant is contingent upon the space available to it. The authors of the new lexicon recommend the following alternative: Canal compromise of less than a third of its AP distance is mild; between one and two thirds is moderate; more than two thirds is severe. The same grading methodology can be applied to the foramen.

Within the disc, one may additionally be able to discern radial fissures or tears, circumferential tears or delamination. Finally, various levels and regions are illustrated above.

References

1. Mendell, T, Wink CS, Zimny ML. Neural elements in human cervical intervertebral discs.Spine 1992;17(2):132-135.
2. Fardon DF, Milette PC. Nomenclature and classification of lumbar disc pathology. Spine2001;26(5): E93-E113.