The postoperative lumbar spine: imaging considerations

The Use of Imaging in Management of Patients with Low Back Pain

Lower back pain (LBP) is one of the most common chief complaints encountered in primary care. Advanced imaging studies, including computerized tomography (CT) and magnetic resonance imaging (MRI), are frequently ordered in the setting of LBP. Structural abnormalities are commonly identified by CT and MRI in patients complaining of low back pain, however, these findings are also found in asymptomatic patients. In the past decade, multiple guidelines have been published to help providers identify patients in whom the use of advanced imaging is appropriate. In this article, we review common conditions associated with LBP that require advanced imaging along with their clinical and associated imaging findings.

Symptomatic nerve root changes on contrast-enhanced MR imaging after surgery for lumbar disk herniation

BACKGROUND AND PURPOSE

The significance of postoperative nerve root changes (enhancement, thickening, and displacement) is still a topic of debate. The purpose of this study was to evaluate the association between nerve root changes and residual or recurrent symptoms after lumbar surgery with contrast-enhanced MR imaging.

MATERIALS AND METHODS

A total of 120 patients with 140 postoperative lumbar disk lesions causing residual or recurrent pain underwent contrast-enhanced MR imaging. The levels at which diskectomies had been performed were retrospectively evaluated for nerve root enhancement (NRE), thickening, and displacement. Association between nerve root changes and corresponding clinical presentations were statistically assessed. Nerve root changes in recurrent disk herniation (RDH) and postoperative epidural fibrosis (PEF) were also evaluated with clinical symptoms.

RESULTS

Ninety-two (65.7%) of the 140 disks demonstrated NRE. Regarding the association with clinical symptoms, the sensitivity was 91.7%, the specificity was 73.2%, the positive predictive value (PPV) was 83.7%, and the negative predictive value was 85.4% (P = .000). Nerve root thickening and displacement were significantly associated with the clinical symptoms, especially when NRE was combined (PPV, 87.7% and 87.2%, respectively). When RDH was combined with all 3 nerve root changes, the PPV was increased up to 94.1%. However, in PEF, the association between nerve root changes and clinical symptoms was not significant unless all 3 nerve root changes were combined.

CONCLUSIONS

In patients with residual or recurrent pain after surgery for lumbar disk herniation, nerve root changes on contrast-enhanced MR imaging were well associated with clinical symptoms, of which NRE was the most significant finding.

Post-operative lumbar spine: comparative study of TSE T2 and turbo-FLAIR sequences vs contrast-enhanced SE T1

AIM

To compare turbo T2 weighted spin echo (TSE T2) and turbo-FLAIR (fluid attenuated inversion recovery) vs gadolinium enhanced T1 weighted spin echo (SE T1) sequence in the differential diagnosis between disc herniation and post-surgical fibrosis.

MATERIALS AND METHODS

Sixty-four patients who underwent surgical treatment for lumbar disc herniation with persistent or recurrent post-surgical symptoms were studied with a 0.5 Tesla MR system. The sequences used were TSE T2, turbo-FLAIR and T1 SE with and without intravenous gadolinium DTPA. The enhanced T1 SE sequence was considered the gold standard. Sensitivity and specificity were calculated.

RESULTS

The sensitivity was 100% for both TSE T2 and turbo-FLAIR sequences. The specificity was 94% for TSE T2 and 92% for turbo-FLAIR. Negative predictive value was 100% for both sequences and positive predictive value 84% and 80% for TSE T2 and turbo-FLAIR, respectively.

CONCLUSION

Although both sequences show high sensitivity, TSE-T2 presents greater specificity than turbo-FLAIR as compared to enhanced T1 SE. TSE T2 also offers the advantage of myelographic effect. We consider that the use of rapid sequences may avoid the need for intravenous contrast medium in most cases, reserving gadolinium DTPA only to those where all the criteria for hernia or fibrosis are not fulfilled.

Subchondral marrow changes after laser diskectomy in the lumbar spine: MR imaging findings and clinical correlation

OBJECTIVE

We examined MR imaging findings and determined the clinical significance of subchondral bone marrow changes in the lumbar spine of holdium:yttrium aluminum garnet laser diskectomy patients.

MATERIALS AND METHODS

We retrospectively reviewed the pre- and postoperative MR images of 109 patients with recurrent radiculopathy, lower back pain, or both 1 year after laser diskectomy of 178 disks. From this group of patients, MR images were also obtained in 11 patients with subchondral marrow changes 5-7 years after surgery. These patients were interviewed regarding residual lower back pain. Thirteen asymptomatic laser diskectomy patients also underwent follow-up MR imaging within 1 year of surgery.

RESULTS

After surgery, subchondral marrow abnormalities were identified in 41 of 109 laser diskectomy patients. The remaining 68 patients had no postoperative subchondral bone marrow changes. Postoperative subchondral marrow changes were not associated with inflammation of the adjacent disk space and did not affect surgical outcome. Bone marrow changes decreased in size in the 11 patients examined 5-7 years after laser diskectomy, and eight of these patients described their lower back pain as improved. In 13 asymptomatic laser diskectomy patients, one new subchondral marrow abnormality was identified.

CONCLUSION

Subchondral marrow abnormalities may occur in the vertebral end plates after holmium:yttrium aluminum garnet laser diskectomy. However, these changes probably do not affect surgical outcomes and appear to resolve over time.