EVALUATION OF THE POSTOPERATIVE LUMBAR SPINE WITH MR-IMAGING - THE ROLE OF CONTRAST ENHANCEMENT AND THICKENING IN NERVE ROOTS

Purpose: Two new signs of lumbar nerve root affection have been report ed in recent years on the basis of MR examinations, namely: thickening in nerve roots; and contrast enhancement in nerve roots. The aim of t his study was to assess contrast enhancement in nerve roots in a stand ardised way, and to evaluate the clinical significance of contrast enh ancement and of nerve-root thickening in the symptomatic post-operativ e lumbar spine. Material and Methods: A total of 121 patients (who had previously been operated on for lumbar disc herniation) underwent 152 MR examinations, mainly on a 1.5 T system. Focal nerve-root enhanceme nt was identified by visual assessment. Intradural enhancement was als o quantified by pixel measurements that compared the affected nerve ro ots before and after contrast administration. Non-affected nerve roots were used as reference. Results: Enhanced nerve roots in the dural sa c increased at least 40-50% in signal intensity after contrast adminis tration compared to pre-contrast images and also compared to non-affec ted nerve roots. Intradural nerve-root enhancement was seen in 10% of the patients and focal enhancement in the root sleeve was seen in a fu rther 26%. Nerve-root thickening was seen in 30%. Good correlation wit h clinical symptoms was found in 59% of the patients with intradural e nhancement, in 84% with focal enhancement, and in 86% with nerve-root thickening. The combination of thickening and enhancement in the nerve root correlated with symptoms in 86% of the patients. Conclusion: Ner ve-root enhancement (whether focal or intradural) and thickening in th e nerve root are significant MR findings in the post-operative lumbar spine. In combination with disc herniation or nerve-root displacement, these two signs may strengthen the indication for repeat surgery. How ever, root enhancement within 6 months of previous surgery may be a no rmal post-operative finding.