45 Postoperative Lumbar Spine Gadolinium chelate contrast agents are routinely utilized in the MRI evaluation of the postoperative spine to distinguish epidural fibrosis (scar) and recurrent disk herniations— both important etiologies of failed back surgery syndrome. There is good specificity for this distinction utilizing contrast-enhanced scans acquired less than 20 minutes following contrast administration at 3 months or more after surgery. Figures 45.1A through 45.1F illustrate this use. On sagittal (A) T1 and (B) T2WI there is a defect in the right L5–S1 lamina as a result of prior posterior decompression surgery. In addition, a low to moderate SI focus of soft tissue protrudes posteriorly at the level of the L5–S1 disk. On the basis of these images alone, such a finding, which appears to extend from the desiccated, compressed L5–S1 intervertebral disk, might be mistaken for a disk herniation. (C) Contrast-enhanced FS T1WI, however, shows this soft tissue focus to enhance uniformly following contrast administration—an appearance consistent with epidural fibrosis or scar. Axial (D) T1, (E) T2, and (F
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