IONIC VERSUS NONIONIC PARAMAGNETIC CONTRAST-MEDIA IN DIFFERENTIATING BETWEEN SCAR AND HERNIATED DISK

PURPOSE: To compare the MR contrast enhancement produced by ionic and nonionic paramagnetic contrast media in herniated disk fragments with that in epidural scar tissue. METHODS: A recurrent herniated disk was modeled in canines by using laminectomy to place a fragment of disk ca rtilage in the epidural space. The dogs were studied 88 and 90 days af ter laminectomy with MR imaging enhanced with an ionic or a nonionic p aramagnetic contrast medium. Contrast enhancement of the epidural scar tissue and the epidural disk fragment was measured at 2, 22, and 45 m inutes after the injection. RESULTS: Contrast enhancement was consiste ntly and significantly higher in scar tissue than in disk fragments, a lthough the difference decreased between 2 and 45 minutes after admini stration of contrast medium. Enhancement of disk fragments was less wi th the ionic than with the nonionic contrast medium. Contrast between the disk fragments and scar was also greater with the ionic than with the nonionic medium. CONCLUSIONS: The contrast between recurrent disk fragments and scar tissue is affected by the timing of the scan and th e choice of contrast medium. Scans obtained immediately after the inje ction of contrast medium show more contrast between disk fragment and scar than do delayed scans. Recurrent herniated disk fragments are mor e effectively shown by ionic than by nonionic media.