Computed tomography in spondylolisthesis.

Fourth generation computed tomography (CT) diagnostic studies were used to investigate or localize, neurologic changes and to clarify the anatomy of slippage in a consecutive series of 31 patients who had spondylolisthesis. Eighteen patients had operative procedures, i.e, either spinal fusions, decompressions, or both, after the CT examinations, and the average follow-up was 25 months. Ten postoperative CT studies were performed to document the correction of the original pathology. Fifteen patients had objective neurologic deficits referable to the spondylolisthesis, of whom CT demonstrated the specific sites of neural encroachment in 13. Preoperative myelography was of limited use; complete block of contrast material occurred, and the etiology of nerve root compression was not visualized. In isthmic spondylolisthesis, CT showed a fibrocartilaginous mass at the pars interarticularis, compressing the adjacent nerve root, as described by Gill et al. In degenerative spondylolisthesis, severe lateral recess stenosis occurred. CT provided diagnostic evidence of a tethered cord in dysplastic spondylolisthesis, if displaced bony fragments in the canal in traumatic spondylolisthesis, and spinal infiltration of neoplasms in the pathologic type. CT is important preoperatively in cases of severe spondylolisthesis and can be used to determine which warrant decompression in addition to fusion. These results also support the concept that neurologic findings associated with spondylolisthesis can be due to a multitude of anatomic abnormalities and should not be simply attributed to a herniated nucleus pulposis at the slip.