Lumbosacral Disc Injuries Workup

Updated: Oct 12, 2015
  • Author: Robert E Windsor, MD, FAAPMR, FAAEM, FAAPM; Chief Editor: Craig C Young, MD  more...
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Workup

Imaging Studies

Discography

Before performing intradiscal, minimally invasive, or most open surgical interventions, localization of the affected disc level must be determined. Discography is currently the only tool that correlates a radiographic image to symptoms and is essential to the diagnosis of IDD.

Lindblom introduced lumbar discography in the early 1940s. [27] During the 1940s-1960s, concerns were raised regarding the safety of this procedure after reports of spinal headache (HA), discitis, meningitis, intrathecal hemorrhage, arachnoiditis, reaction to inadvertent intradural injection, and damage to the disc itself. In 1948, Hirsch reported on 16 patients who underwent discography with no complications and who later showed no signs of disc injury from discography when operated on. [28]

Much of the controversy surrounding discography centers on the unfavorable results reported by Earl Holt in 1968. [29] He examined 30 prison inmates (70-72 discs) and reported a 37% false-positive rate in asymptomatic volunteers. The shortcomings of this paper were extensively and critically reviewed by Simmons et al. [30] As these authors pointed out, the procedure of discography has changed significantly since Holt's study and should not be discounted based solely on those earlier results. In the same year as Holt's report, Wiley et al showed that the value of discography was in the investigation of symptoms that arise from the disc in the absence of herniation. [31] This study involved over 1000 patients and more than 2500 discs.

Walsh and associates reported on lumbar discography in normal subjects. [32] In asymptomatic subjects, the discogram alone was abnormal in 17%. When the criteria for a positive discogram included a concordant pain response, none of the subjects were positive.

Discography provides information about the structure and sensitivity of discs that may not be learned from other sources. Discographic pain provocation is a very important part of the evaluation. Currently, discography is the only method of directly relating a radiographic image to a patient's pain.

In 1995 the NASS published its position statement regarding discography. [33] This procedure is indicated when adequate conservative therapy and noninvasive tests have not provided adequate information. Specific indications include the correlation of an abnormal disc with clinical symptoms and persistent severe symptoms without clearly identifying the disc as the pain source.

Discography is also indicated in the assessment of patients in whom surgery has failed and in the assessment of discs before fusion or minimally invasive interventions. The minimum recorded information should include the resistance to injection, amount of contrast medium injected, the pattern of dye distribution (eg, diffuse, location of fissures, extravasation, herniations, Schmorl nodes), and pain response. Special attention to the pain response is important (eg, no pain, dissimilar pain, similar pain, exact pain reproduction).

Classification

A classification method for CT scanning/discography was proposed in 1987 and is widely accepted today for reporting the degree of intervertebral disc degeneration, annular disruption, and provoked pain response. [34] The Dallas Discogram Description (DDD) classifies a discographic procedure based upon the disc morphology as seen on CT scans and the provoked pain response. The DDD identifies 4 classes of annular disruptions, as follows [34] :

  • Grade 0 is defined as contrast medium entirely within a normal nucleus pulposus.

  • Grade 1 is used if the contrast medium extends radially along a fissure involving the inner third of the annulus fibrosus.

  • Grade 2 is defined as the extension of the contrast medium into the middle third of the annulus fibrosus.

  • Grade 3 is defined as the extension of the contrast medium into the outer third of the annulus, either focally or radially within the outer annulus to an extent not greater than 30º of the disc circumference.

  • A grade 4 was added by Aprill and Bogduk, defined as a grade 3 tear that dissects radially within the outer third of the annulus to involve more than 30º of the disc circumference. [35]

  • Schellhas et al added a grade 5, defined as a full-thickness tear, either focal or more circumferential, with extra annular leakage of the contrast medium. [36]

  • The second component of the DDD is the provoked pain response. Upon pressure challenge with an injectate, pain responses are categorized as no pain, dissimilar pain, similar pain, or exact pain reproduction.

The classification of disc injuries based upon radiographic imaging can be confusing due to the multitude of terms relating to disc abnormalities. Common terms describing a disc abnormality include bulge, protrusion, herniation, rupture, and extrusion. Often, a modifier such as focal, contained, noncontained, subligamentous, sequestered, or free fragment, accompanies each of these categories. Other descriptions use a combination of terms (eg, extruded herniation).

In a review of magnetic resonance images (MRIs) of the spine, Gundry and Fritts defined the disc abnormality nomenclature. [37]

  • A bulge refers to a broad-based projection of the outer annular fibers beyond the posterior bony margins of the adjacent vertebrae. A bulging disc may or may not be associated with an annular tear, resulting in the more descriptive terminology of an annular tear with focal annular bulge.

  • The term herniation refers to the presence of nuclear material within or beyond the confines of the annular tear. A contained herniation is one that is contained beneath an intact posterior longitudinal ligament, whereas a noncontained herniation extends through a defective posterior longitudinal ligament. A sequestered or free fragment herniation denotes a herniation that has no connection with the original disc.

Other authors have proposed a simpler nomenclature. In this classification, intervertebral discs are classified as normal, bulge, protrusion, or extrusion. These terms are defined as follows:

  • Normal – No disc extension beyond the interspace

  • Bulge – Circumferential symmetric extension of the disc beyond the interspace (around the endplates)

  • Protrusion – Focal or asymmetric extension of the disc beyond the interspace, with the base against the disc of origin broader than any other dimension of the protrusion

  • Extrusion – More extreme extension of the disc beyond the interspace, with the base against the disc of origin narrower than the diameter of the extruding material itself or with no connection between the material and the disc of origin

All these classification terms are attempts to describe in detail the findings of MRIs with their increased ability to distinguish between the nucleus pulposus, annulus fibrosus, and posterior longitudinal complex. In and of themselves, degenerative, bulging, protruding, or extruding discs are not known to be painful. Some combination of mechanical and biochemical insults produces the pain related to lumbosacral intervertebral disc injuries.

Aprill and Bogduk described a finding on MRI that was related to an annular tear, which became known as the high intensity zone (HIZ). [35] The authors postulated that the HIZ was a marker for a painful lumbar disc. The criteria for identifying an HIZ were a high-intensity signal (bright white) located in the substance of the posterior annulus fibrosus, clearly dissociated from the signal of the nucleus pulposus in that it is surrounded superiorly, inferiorly, posteriorly, and anteriorly by the low-intensity (black) signal of the annulus fibrosus, and it is appreciably brighter than that of the nucleus pulposus.

Aprill and Bogduk found the HIZ to be a diagnostic indicator of a degenerated painful disc such as that seen in IDD. [35] Their findings remain debated. [38, 39] Some authors have provided evidence supporting the HIZ, whereas other results have contradicted their findings. It is postulated that the HIZ is composed of nuclear material in the annulus fibrosus, which has become inflamed, neovascularized, or invaded by granulation tissue.