Lumbar spine after surgery: examination with intravenous contrast-enhanced CT

The grading model for the assessment of the total amount of epidural fibrosis in postoperative lumbar spine

Purpose

To present a new model derived from Ross’s model for the assessment of the total amount of epidural fibrosis and to present inter- and intravariability study.

Methods

Two readers blinded to each other and blinded to their first and second reading retrospectively evaluated the magnetic resonance examinations in 32 postoperative spine surgery patients using this model.

Results

Paired and unpaired two-sided t tests showed no significant difference between the first and second reading, and interclass correlation coefficient revealed good interobserver reliability.

Conclusion

The proposed model enables estimation of the amount of epidural fibrosis in postoperative lumbar spine and does not require any additional software or hardware. It is designed for multi-centered clinical studies where it is necessary to compare the values of epidural fibrosis between the tested and control group. The use of the proposed model is fast and practical and helps to avoid complications arising from image format, calibration and software, which are often encountered in multi-centered studies.

Use of computed tomographic densitometry to quantify contrast enhancement of compressive soft tissues in the canine lumbosacral vertebral canal

OBJECTIVES

To evaluate computed tomography (CT) densitometry as a technique for quantifying contrast enhancement of compressive soft tissues in the canine lumbosacral vertebral canal and to determine whether the degree of contrast enhancement can be used to help predict tissue type or histopathologic characteristics.

ANIMALS

29 large breed dogs with lumbosacral stenosis.

PROCEDURE

Contrast-enhanced CT of L5-S3 was performed by use of a previously described protocol. At each disk level, CT densities of a water-filled syringe, epaxial muscles, and 4 vertebral canal locations were measured. Mean tissue enhancement was calculated by vertebral canal location, using water-filled syringe enhancement as a correction factor. Corrected CT enhancement was compared with tissue type, degree of tissue inflammation, and degree of tissue activity.

RESULTS

Intravenous contrast administration of contrast medium significantly increased CT densities of water-filled syringes and epaxial muscles. Corrected CT enhancement of vertebral canal soft tissues at stenotic sites was greater than at nonstenotic sites. There was no association between enhancement and tissue type for any vertebral canal location. There was no correlation between enhancement and degree of tissue inflammation. There was a correlation between enhancement and tissue activity in the dorsal vertebral canal only.

CONCLUSIONS AND CLINICAL RELEVANCE

A water-filled syringe is a useful calibration tool for CT density measurements. The degree of tissue contrast enhancement, measured by CT densitometry, can be helpful for predicting the location of compressive soft tissues in dogs with lumbosacral stenosis. However, it is of limited value for predicting compressive soft-tissue types or histopathologic characteristics.

MAGNETIC RESONANCE IMAGING IN FAILED BACK SURGERY SYNDROME

The failed back surgery syndrome (FBSS) is a severe, long-lasting, disabling and relatively frequent (5-10%) complication of lumbosacral spine surgery. Wrong level surgery, inadequate surgical techniques, vertebral instability, recurrent disc herniation, and lumbosacral fibrosis are the most frequent causes of FBSS. The results after repeated surgery on recurrent disc herniations are comparable to those after the first intervention, whereas repeated surgery for fibrosis gives only 30-35% success rates, and 15-20% of the patients report worsening of the symptoms. MRI has allowed a differentiation between these two pathologies for selection of different therapies. Gadolinium enhanced MR is at present the single most sensitive and specific imaging modality available to the neuro radiology imager for the evaluation of the post operative lumbosacral spine in the patient presenting with FBSS. Medical imaging specialists and clinicians need to better understand the origins and means of avoiding the FBSS, to more clearly focus the post operative imaging evaluation and to more successfully link the clinical diagnosis and the imaging findings with optimised patient therapy.

Evaluation of canine lumbosacral stenosis using intravenous contrast-enhanced computed tomography

The objective of this study was to evaluate intravenous contrast-enhanced computed tomography as a technique for predicting the within-level location(s) of compressive soft tissues in the canine lumbosacral spine. Pre-operative intravenous contrast-enhanced computed tomography of the L5-S3 vertebral levels was performed in 12 consecutive large breed dogs with lumbosacral stenosis. The images were evaluated for enhancement of soft tissues by two radiologists who were unaware of the surgical findings. For each within-level location (dorsal canal, ventral canal, right lateral recess, left lateral recess) enhancement was classified as present, absent or equivocal. The results were compared with the results of surgical exploration and histopathology of excised tissues. The positive predictive values of intravenous contrast-enhanced computed tomography for compressive soft tissues involving the dorsal canal, ventral canal and lateral recesses were 83%, 100%, and 81% respectively. Negative predictive values for compressive soft tissues involving these locations were 29%, 50%, and 40% respectively.

Plain CT of the degenerative lumbar spine

Degenerative processes of the lumbar spine consist of several disorders of various etiologies with different radiological manifestations. Computed tomography (CT) is well suited for evaluation of these processes since contours of soft tissues, subtle bone structure changes and small calcifications are easily demonstrated with this technique. Spiral CT scanning provides fast data acquisitions, and volumes of high quality for multiplanar reformatting. This review article describes the CT scanning techniques and diagnostic findings of the most common degenerative processes of the lumbar spine.

Early postoperative MRI findings following surgery for herniated lumbar disc. Part II: A gadolinium-enhanced study

The aim of our study was to evaluate the contrast-enhanced MR imaging (MRI) findings, in the early postoperative period, in unselected patients undergoing lumbar microdiscectomy (15/16 had total resolution of their symptoms). Contrast-enhanced imaging studies were performed, in all 16 patients of our series, before surgery, and at the third postoperative day and, two months after surgery. Postoperative paraspinal muscles enhancement was present in all patients. In the postoperative period, nerve root enhancement was present in 5/16 patients at the early survey and persisted in one after two months. A pseudohernia depicted as epidural intermediate signal intensity tissue, was seen in 13 patients at the third day MRI, and only in eight after two months. This pseudohernia enhanced peripherally in 8/13 patients and enhanced homogeneously in the remaining five at the first postsurgical examination; in the late MRI the peripheral enhancement was appreciable in only two patients while a homogeneous enhancement was observed in six. Clinical symptoms resolved completely in 14/16 patients on clinical evaluation at the third postoperative day, while the remaining two patients showed residual symptoms and signs of radicular compression. At the early MRI these two patients showed intradural nerve root enhancement. Two months later, one patient did not show the previously described nerve root enhancement and improved clinically, while the other had a positive Straight Leg Raising Sign with persistent intradural nerve root enhancement. In conclusion, no correlation between clinical course and contrast-enhancement of pseudohernia and extradural nerve root was appreciable, although intradural nerve root enhancement seems to represent a clinically relevant finding.

Contrast enhancement pattern and frequency of previously unoperated lumbar discs on MRI

Enhancement frequency and patterns (linear intradiscal, nodular intradiscal, and peridiscal) of the 210 previously unoperated lumbar discs were evaluated using contrast-enhanced lumbar MRI. They also were compared with morphologic abnormalities (normal, bulging, protruded, and extruded) and signal alteration (high signal on T2-weighted images) of the disc. Image interpretation was decided by the consensus of two musculoskeletal radiologists. Enhancement was observed in 69 (32.6%) discs. The enhancement patterns were either intradiscal, linear of (79.7%) or nodular (10.2%), peridiscal (7.2%), or combined (2.9%). Thirty-five (77.8%) of the 45 herniated discs, 35 (77.8%) were enhanced, whereas 34 (20.6%) of 165 normal-appearing disc were enhanced. Enhancement was observed more frequently in discs with high signal intensity zones (P < 0.05). In the six patients with enhanced discs, surgery revealed granulation tissue in three extruded discs, two protruded discs, and one bulging disc. The authors believe that contrast enhancements are frequent in herniated discs and are not infrequent in normal-appearing discs. The understanding of various enhancement patterns may help in the interpretation of lumbar spine MRI.

Early postoperative MRI findings following surgery for herniated lumbar disc

MRI is routinely used in the evaluation and management of patients with failed back surgery syndrome (FBSS). However, its value is unclear in the early detection of signs that can negatively affect that later course of surgical cases. The purpose of the present study is to describe the MR images of early postoperative MRI at 3 days in 30 unselected patients who underwent lumbar microdiscectomy, and to correlate the findings with follow up MRI at 8 weeks and with final outcome. The findings are correlated with literature data. Early postoperative MRI findings were consisting of pseudohernia in 24 patients (80%), annular rent in 23 patients (80%), and other non-specific postoperative findings. On the late MRI the pseudohernia persisted in 12 patients (50%), the annular rent in 4 patients (15%) and asymptomatic pseudo-spondylodiscitis was apparent in 3 patients (10%) as was a case of true spondylodiscitis. Therefore, early postoperative findings have limited value in the management of patients after surgery for lumbar disc herniation, since the images were not correlated with the immediate clinical course after surgery nor with the late radiological and clinical outcome. The evident imaging changes in the early postoperative period after lumbar disc surgery limit the accuracy of the interpretation of MRI examinations.

Contrast enhanced computed tomography and magnetic resonance imaging in the diagnosis of recurrent disc herniation

A positive result of re-operation in patients with recurrent symptoms after lumbar disc surgery is likely only if a new disc herniation is present. An improved ability to differentiate between recurrent disc herniation and scar tissue by contrast enhanced CT and MRI is suggested in earlier studies. In a prospective study 29 patients were selected for operation for suspected recurrent disc herniation. The inclusion of the patients was based on clinical symptoms and signs and myelography or non-enhanced CT. All patients were examined by CT and MRI both with and without intravenous contrast pre-operatively. The examinations were evaluated blind on a five point scale and statistical analysed by a regret function. Intravenous contrast improved the diagnostic power of both CT and MRI. MRI was superior to CT in both non-enhanced and enhanced examinations. MRI with intravenous contrast enhancement is proposed as the primary examination in patients with suspected recurrent disc herniation.

MRI after successful lumbar discectomy

Our aim was to establish the normal range of MRI findings after successful lumbar discectomy. We prospectively examined 34 consecutive patients with an excellent clinical outcome by MRI 6 weeks and 6 months after surgery. All examinations included sagittal and axial spin-echo (SE) T1-weighted images before and after intravenous gadolinium-DTPA and fast SE T2-weighted images. Contrast enhancement along the surgical tract was seen in all patients 6 weeks and 6 months after surgery. After 6 months minimal or no mass effect on the dural sac by epidural scar was seen. In 20% of patients there was recurrent disc herniation, with mass effect. Enhancing nerve roots were seen in 20% of patients 6 weeks postoperatively, and half of these were associated with recurrent disc herniation at the same side. None of these patients still showed nerve root enhancement 6 months after surgery. Postoperative MRI studies must be interpreted with great care since the features described in the failed back surgery syndrome are also found, to some extent, in asymptomatic postoperative patients.

Magnetic resonance imaging, computed tomography, and myelography in the diagnosis of recurrent lumbar disc herniation

Thirteen patients with recurrent symptoms after lumbar discectomy were evaluated. All the patients were enrolled in the study on the basis of clinical symptoms and signs only. The patients were examined with MRI, CT, and myelography in order to compare a) the clinical findings with the imaging investigations, b) the predictive value of the different investigations, and c) the clinical and investigative results with the operative findings. All patients were operated upon according to the clinical findings, and the surgical results were used as the final diagnosis. In six patients a new disc herniation was detected. In the remaining cases surgery revealed either scar tissue or nothing to explain the recurrence of the symptoms. The three imaging modalities were analysed by receiver operating characteristic (ROC) curves. The areas under the ROC curves were 0.68 for MRI, 0.83 for CT, and 0.43 for myelography. The difference in areas between CT and myelography was significant (p less than 0.05). The results indicate that CT has the highest predictive value for demonstrating the recurrence of a lumbar disc herniation.

Magnetic resonance imaging of the spine

Magnetic resonance (MR) imaging offers the advantages of multiplanar capabilities, physiologic as well as anatomic imaging, and some tissue specificity. Since mid-1985, we have performed more than 2,800 MR examinations of the spine, and gadolinium has been used as a contrast agent in many MR studies since its release by the Food and Drug Administration last year. Although MR imaging has been promoted as the procedure of choice for all clinical indications, on the basis of our experience myelography still plays an important role in the imaging of many spinal disorders, including disk disease. Some pathologic conditions such as intraspinal vascular malformations and leptomeningeal metastatic lesions are best imaged by myelography. MR studies have been most useful in evaluating intraspinal neoplasms, spinal cord parenchymal lesions, infections, congenital abnormalities, and "postoperative failed back syndromes."

CT-diskography in the evaluation of the postoperative lumbar spine. Preliminary results

Thirty-three patients with recurrent sciatica after lumbar-disk surgery were studied for recurrent herniated nucleus pulposus (HNP) by CT alone and CT-diskography (CTD). Twenty-six patients underwent surgical reexploration allowing correlation with CTD. CTD made a correct diagnosis of recurrent HNP in twenty-one patients showing an extravasation of the contrast medium from the disk space into the medullary canal. In two cases CTD was positive for recurrent HNP but surgery showed only fibrosis. The amount of contrast leak was very small in these two cases along the posterior common longitudinal ligament, and the junction with the disk was very narrow. Because of their clinical presentation three patients with negative studies were operated upon. One showed only fibrosis and the two others showed an associated disk fragment. Among the twenty-one true-positive cases, seven showed a combination of recurrent HNP and scarring. Contamination of CSF by the contrast medium through the dura was observed in two patients. Although a prospective comparative study between CTD and IV-contrast-enhanced CT is necessary, CTD appears to be a useful diagnostic procedure for recurrent HNP after surgery of the lumbar spine.