Minimally-Invasive, Interventional Spine Treatment Part II
Diagnostic Provocation Discographic Injections
Lumbar provocation discography remains a controversial diagnostic technique; and even more so with cervical/ thoracic discography. To appreciate the historical controversy surrounding discography is to understand that its inception was a tenuous one, tainted by admonitions, suppositions, and contradictions. Proponents believe discography uniquely shows internal disc anatomy and identifies clinically symptomatic (painful), or asymptomatic (non-painful) discs. In 1934, Mixter and Barr first called attention to the pathoanatomy of the herniated lumbar disc and its relationship to radicular dysfunction from neural compression. In 1952, Pierre Erlacher established the correlation of the nucleogram to nuclear anatomy by investigating cadaveric discs using contrast material and histological stains. The precise technique for lumbar discography was described in 1952 by Cloward and Busaid. Since those initial procedures were performed, improved techniques and technological advances and a better understanding of pain have provided much needed refinement of discography as a potentially valuable diagnostic test.
The presence of degenerative disc changes does not necessarily correlate with clinical symptoms or a painful internal disc. Provocative diagnostic testing for concordant discogenic pain is the most important aspect of discography and provides information regarding the clinical significance of concordant disc abnormalities. There is literature that suggests that the presence of outer annular fissures/ruptures (i.e., HIZ, high intensity zones) are significant predictors of a painful degenerative disc rather than the degree of disc deterioration. CT-discography has been shown to have higher sensitivity and specificity than individual CT scans, myelography, and CT-myelography for internal disc disruption (IDD, a chemically-mediated abnormality of the nucleus pulposus and annulus fibrosus with/without disc contour defects), herniated nucleus pulposus (HNP), recurrent disc herniation, and foraminal disc herniation. CT-discography interpretation is highly reproducible for grading annular degeneration and disruption (e.g., Dallas Discography Criteria). The presence of a high intensity zone (HIZ) on magnetic resonance imaging (MRI) has been shown to correlate 100% with an outer annular rupture by CT-discography imaging, although 54% of discs with annular ruptures did not show a HIZ on MRI. The sensitivity and specificity of an HIZ in identifying those discs that exactly reproduce discographic pain was 82% and 89%, respectively. Although MRI with gadolinium may be more accurate than CT-discography in distinguishing recurrent disc herniations from postoperative scar tissue, CT-discography is more sensitive than myelography, CT scans, or CT-myelography for determining intradiscal morphology. At the present time, MRI does not appear to be as sensitive or specific as CT-discography in determining whether or not a disc is symptomatic. Discography and CT-discography have found abnormalities despite normal MRI scans and, conversely, found asymptomatic discs in the presence of significantly abnormal MRI studies. Although MRI can reliably detect disc degeneration and, in certain cases, predict painful annular ruptures, many believe that only provocative discography can consistently determine the presence or absence of symptomatic annular ruptures/fissures.
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