Figure 2a. Degenerative disk protrusion in a 48-year-old woman with low back pain, a positive diskogram, and a concordant pain response at the L5-S1 disk level. (a) Diskogram shows a normal appearance at the L3-4 intervertebral space. The abnormal L4-5 intervertebral space shows focal extension of the diskographic dye (arrow) into the ventral epidural space and the abnormal-appearing L5-S1 disk, the site of concordant pain, although no posterior extension of dye is seen there. (b) Postdiskographic CT scan at the L4-5 interspace clearly depicts the posterior extension of the diskographic dye (arrow) into the ventral epidural space through the annular defect. Despite this appearance, no pain was elicited at the L4-5 intervertebral space level.