Pathologic characteristics and clinical significance of high intensity zone of lumbar intervertebral disc in the patient with discogenic low back pain

Objective To study the pathologic characteristics and clinical significance of high intensity zone (HIZ) of lumbar intervertebral disc in the patients with discogenic low back pain. Methods 52 patients with low back pain without disc herniation underwent MRI and following discography of lumbar vertebrae. All patients previously were treated conservatively without relief of their symptoms for more than 6 months. Specimens of lumbar intervertebral discs containing HIZ in the posterior annulus from 11 patients with discogenic low back pain during posterior lumbar interbody fusion (PLIF) were collected to investigate the morphologic patterns and clinical significance. Results In all of 142 discs in 52 patients at discography, 17 discs in 17 patients presented HIZ, all showed painful reproduction and abnormal morphology with annular tears extending either well into or through the outer third of the annulus fibrosus. The histologic study of the consecutive sagittal slices in the HIZ lesions revealed that the normal lamellar structure was replaced by disorganized, vascularized granulation tissue that consisted of small round cells, fibroblasts, and newly formed blood vessels around the tears extending from the nucleus pulposus to the outer region of the annulus fibrosus. Blood vessel proliferation and inflammatory cell infiltration were seen extending along the margins of the tears into the middle and inner annulus, and sometimes the tears were bridged with granulation tissue. Ingrowth of vascularized tissue was sometimes observed to end abruptly at the junction between the inner third of the annulus and the nucleus pulposus. There was also matured scarring collagenous tissue. Conclusion The HIZ in the lumbar disc in the patients with symptomatic low back pain can be considered as a reliable marker of painful outer annular disruption.