Computed tomography in low back pain before and after myelography. A qualitative comparison

Forty-six patients with possible lumbar disk herniation were examined with computed tomography (CT) before and after lumbar myelography with metrizamide. Altogether 90 intervertebral spaces (L4/L5 and L5/S1) were analyzed with regard to the diagnostic information provided by pre- and postmyelography CT. Corresponding to the level of 73 intervertebral spaces (81%) the contrast medium filling of the dural sac was homogeneous, while corresponding to 17 spaces (19%) the filling was inhomogeneous, with layering of contrast medium. The demarcation of the disk margin and of the dural sac was poor at the level of 13 spaces (14%), the majority of which (9 spaces) belonged to the group with homogeneous dural sac filling. At the level of 4 intervertebral spaces the dural sac was isodense with the intervertebral disk. The overall diagnostic information from the premyelography examination was equal to the postmyelography examination at 66 intervertebral spaces (73%). The postmyelography CT examination showed the details better than the conventional CT at 11 intervertebral spaces (12%), and poorer than conventional CT at 13 intervertebral spaces (15%). It is concluded that in general a conventional CT examination is adequate in the evaluation of patients with suggested intervertebral disk herniation. The need for a postmyelography CT examination can be specified on the basis of the findings at myelography.