[Respective importance of the intradural contrast examination and of the scanning in operable sciatica]

It is not always possible to determine the numerical predictive values of two different diagnostic tests such as contrast studies with myelography and evaluation by CT scan in the preoperative evaluation of sciatica. The reliability of these predictive calculations can be subject to error. However, the concordant results of most studies favor the CT scan. We have given the predictive values of these tests as mentioned in the literature along with our own series comparing these two methods. Overall, the CT scan is though to be a better diagnostic tool for medio-lateral herniated discs at the L5-S1 level which are not seen using amipaque due to the greater thickness of the epidural space and for lateral herniations at the L4-L5 and L5-S1 levels. Thus, the Ct scan evaluates more completely the anatomy of the lateral recesses. This is particularly helpful when the anatomical findings differ from that of a classical herniated disc, for example in elderly patients. With amipaque, whose diagnostic yield could be improved by a more careful reading of the roentgenograms, its usefulness lies in the ability to evaluate the entire length of the lumbosacral canal down to the conus medullaris, and gives a better view of the course of the nerve roots.