Internal disc disruption (IDD) is a term that was coined in the 1970s to describe pathologic changes of the internal structure of the disc. Internal disc disruption and degeneration involve a physiochemical change in the gly-cosaminoglycans of the NP, which act to bind water; over time this water-binding capacity diminishes. Disc degeneration is usually heralded by loss of hydration and thus decreased T2 signal on MRI. However, focal T2 bright areas reflecting annular tears indicate fragmentation of the outer collagenous AF. Hyperintense zone (HIZ) is the term that has been coined to denote this finding on T2-weighted MR images (Fig. 4). In the patient population undergoing MRI for lumbar back pain, this finding may be noted in
Fig. 2. (A) Sagittal MRI showing a disc herniation (sequestered disc). Incidental note is made of a vertebral body hemangioma (star). (B) Sagittal MRI showing a large disc herniation at L5-S1 with the disc material tracking posterior to the L5 vertebral body.
Fig. 3. (A, B) Sagittal and axial MRI showing a free disc fragment compressing the exiting nerve root (white arrowhead) in a patient with severe radiculopathy.
approx 25% (12,13). The presence of an HIZ correlates with an annular tear and an approx 85-87% chance that there will be concordant pain reproduction at discography (12,14,15). An HIZ may enhance after contrast administration, reflecting the fibrovascular ingrowth into the region of the annular tear (Fig. 5). In addition, nerve tissue has also been seen by histology in this lesion and is the purported mechanism by which peripheral annular tears generate pain. The prognostic or therapeutic significance of this finding has not yet been elucidated and asymptomatic HIZs may also be encountered.
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