THE POSTOPERATIVE LUMBAR SPINE - A RADIOLOGICAL INVESTIGATION OF THE LUMBAR SPINE AFTER DISKECTOMY USING MR-IMAGING AND CT

Problems and Aims: The clinical outcome of repeat lumbar discectomy is not as satisfactory as that of the primary surgical procedure. One re ason is the difficulty of assessing postoperative radiological investi gations and particularly the significance of the various radiological changes. A second problem is differentiating between the two forms of post-operative discitis, a rare but important complication after lumba r discectomy. The aims of this study were: to improve understanding of the significance of certain post-operative radiological changes; and to evaluate differences in the MR features of septic and aseptic post- operative discitis. Material and Methods: A total of 192 patients (209 disc levels) look part in this study; all had had prior lumbar discec tomy. Nineteen of these patients were regarded as asymptomatic and the y served as a control group in the evaluation of certain post-operativ e changes in the symptomatic patients. Twelve patients with post-opera tive discitis were examined in order to compare the MR features of sep tic and aseptic discitis. MR imaging was performed first without and t hen with contrast enhancement in all patients. Contrast-enhanced MR im aging was also compared with contrast-enhanced CT. Results: Owing to i ts superiority in distinguishing the nerve roots at the surgical site, MR imaging was found to be a more valuable diagnostic method than CT. Disc herniations were found in 16% of the disc levels in asymptomatic patients and in 38% of the disc levels in the symptomatic patients. S ignificantly more disc herniations were found in patients who had only a short duration of recurrent symptoms (maximum 3 months) before MR i nvestigation than in the asymptomatic patients. Nerve-root displacemen t due to disc herniation was also significantly more frequent in patie nts with the short symptom duration than in patients with a longer sym ptom duration. True intradural nerve-root enhancement was found in 7% of symptomatic patients, and focal enhancement in the root sleeve was found in 26% of them; there was good correlation to clinical symptoms and other pathological findings. Thickened nerve roots were found with equal frequency in asymptomatic and symptomatic patients. Epidural sc ar tissue diminished with time, showing no significant difference betw een asymptomatic and symptomatic patients. Out of 6 patients with sept ic post-operative discitis, 3 showed extensive MR changes; the remaini ng 3 showed moderate changes which were similar to those in another 6 patients who had aseptic discitis. Discussion and Conclusion: MR is th e imaging method of choice in the evaluation of patients with recurren t clinical symptoms after disc surgery. Disc herniations may be found in asymptomatic patients; it is therefore important to assess the plau sibility of the assumption that the finding of a herniated disc correl ates well with the actual clinical symptoms. Nerve-root displacement a nd nerve-root enhancement caused by recurrent disc herniation may stre ngthen the indication for repeat discectomy. On the other hand, the fi nding of a thickened nerve root seems to be of no diagnostic value. Th e MR features in post-operative discitis develop only gradually and th e differentiation between septic and aseptic forms of discitis is thus difficult at the early stage.