Gadopentetate dimeglumine-enhanced MR imaging of the postoperative lumbar spine: comparison of fat-suppressed and conventional T1-weighted images.

OBJECTIVE: Gadopentetate dimeglumine-enhanced T1-weighted MR imaging has been used to distinguish epidural fibrosis from recurrent disk herniation in the postoperative lumbar spine. Potential interpretative difficulties relate to detection of subtle contrast enhancement and distinction of enhanced tissue from surrounding epidural fat. The objective of this study was to evaluate the utility of fat-suppressed T1-weighted imaging in improving the depiction of postoperative abnormalities. SUBJECTS AND METHODS: Forty-one patients with recurrent signs and symptoms after previous laminectomy and diskectomy were examined with conventional and fat-suppressed T1-weighted imaging before and after IV administration of gadopentetate dimeglumine. MR images were analyzed for the presence or absence of an epidural soft-tissue mass located anterior and/or lateral to the thecal sac. When such masses were identified, their contrast enhancement behavior was characterized according to the volume, intensity, and pattern of enhancement. Epidural fibrosis was diagnosed by using established MR imaging criteria. In patients with evidence of recurrent disk herniation, diagnosis was based on surgery in six patients and on MR imaging findings in the remainder.
RESULTS: Soft-tissue masses were present at 32 of the 43 levels operated on, representing epidural fibrosis (n = 21) or disk herniation (n = 11). Fat suppression improved depiction of contrast enhancement associated with sites of epidural fibrosis. The extent, intensity, and homogeneity of enhancement was greater with fat suppression than with conventional imaging, although the ability to distinguish epidural fibrosis from recurrent disk herniation was not improved.
CONCLUSION: Use of the fat-suppression technique results in increased relative intensity and homogeneity of contrast enhancement associated with sites of epidural fibrosis. However, it does not result in significant improvement in the ability to differentiate fibrotic tissue from recurrent disk herniation. Fat suppression does not appear to be indicated for routine use in imaging of the postoperative lumbar spine, but may be useful as a problem-solving tool in selected patients.