Computed tomography of the postoperative intervertebral disc and lumbar spinal canal: investigation of twenty-five patients after successful operation for lumbar disc herniation.

Twenty-five patients with good outcome after operation for lumbar disc herniation underwent unenhanced computed tomography (CT) and plain radiography of the lumbar spine before, 5 to 7 days after, and 6 to 7 weeks after the operation to define the radiological features of the postoperative disc and spinal canal. After operation, the center of the disc appears hypodense. The anterior and lateral borders remain sharply delimited, but in 44% of the cases the posterior border shows an image suggesting the persistence of disc herniation. In 84% of the cases, there are major changes in the spinal canal with complete occlusion of the extradural space on the operated side by a heterogeneous material the attenuation value of which ranged between those of cerebrospinal fluid and disc. The outline of the dural sac and of the nerve root is lost. This aspect did not significantly change between the 1st and the 6th postoperative week, except for the disappearance of any air within the canal and a slight movement on the dural sac toward the operated side. From these major radiological modifications found in asymptomatic postoperative patients, it is concluded that positive CT in patients with the failed back surgery syndrome has limited value. Myelography is preferred as the primary neuroradiological investigation.