Contrast-enhanced computed tomography scanning of the postoperative spine

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.

Postoperative lumbar MR imaging with contrast enhancement. Comparison between symptomatic and asymptomatic patients

PURPOSE AND MATERIAL: Contrast-enhanced MR imaging of the spine after surgery for lumbar disk herniation almost always shows pathologic changes. To investigate to what extent these changes are correlated to patients' actual clinical symptoms, we compared the postoperative MR findings in 19 asymptomatic patients with 42 symptomatic patients (43 levels).

METHODS

The asymptomatic patients underwent MR examination one year after surgery. Twenty-six of the symptomatic patients underwent MR one year or less after surgery, and in 16 patients (17 levels) MR was performed more than one year after surgery.

RESULTS

Sixteen percent of the asymptomatic and 42% of the symptomatic patients had disk herniation at the level of previous surgery. Most of the herniated disks were found in the symptomatic patients less than one year after surgery. The amount of epidural scar tissue, displacement and thickening of nerve roots, and compression of the dural sac were also studied. Disk herniation as a probable cause of recurrent sciatica was a common finding among symptomatic patients examined one year or less after surgery. In comparing asymptomatic patients and symptomatic patients with more than one year between surgery and MR examination, no significant radiologic differences, including disk herniation, were found.

The role of early postoperative CT scan following surgery for herniated lumbar disc

40 patients underwent lumbosacral microdiscectomy in a 12 months period covering the years 1988-1989 in our center. For the purpose of the present study, we considered the 30 cases who underwent CT control of the operated interspaces and of the adjacent vertebral endplates. This was routinely carried out on the 3rd post-operative day. The present study failed to show correlations between early post-operative CT data and subsequent clinical results in this unselected series of patients. In fact an image suggesting persistent disc herniation was as a rule observed in spite of satisfactory clinical results, and other CT findings that have been considered of clinical significance, such as intraspinal air and low attenuation of disc space, were commonly observed in patients with an uncomplicated post-operative course. The present study suggests that early post-operative CT appears to be of no value in the management of potential early complications of low-back surgery. The introduction of MRI appears to offer other possibilities in the evaluation and management of failed back surgery syndrome (FBSS).