Contrast-enhanced MRI versus myelography and contrast-enhanced CT in postdiskectomy problems

The differentiation between scar tissue and disk herniation is essential in postdiskectomy problems of the lumbar spine, since reoperation on scar tissue alone is often unfavourable. Epidural scar is a vascularized tissue, and enhancement can be seen after intravenous contrast injection, allowing differentiation from avascular disk material. Ten patients who had previously undergone surgery for lumbar disk herniation and with recurrent symptoms severe enough to warrant repeat surgery were examined by myelography, magnetic resonance imaging (MRI), and computed tomography (CT) before reoperation. MRI was performed with T1- and T2-weighted sequences in sagittal and axial projections before and after intravenous contrast injection. CT scans were obtained before and during intravenous contrast infusion. Reoperation revealed scar tissue, alone or together with disk, in 9 of 10 patients. Enhancement of scar but not of disk material was observed on MRI in 8 cases, but in none on CT. No enhancement of disk was seen with either modality. The correct diagnosis was given by MRI in 9 of 10 patients and by CT in 3 of 10. CT was superior to MRI in only 1 patient, who had a bony stenosis. Myelography could not separate disk from scar in any case. In conclusion, contrast-enhanced MRI was superior to MRI without contrast, CT before and after contrast, as well as myelography in discriminating disk from scar tissue.