Occult spinal dysraphism: neuroradiological study.

We present a retrospective study of occult spinal dysraphism in 47 children aged 0 to 14 years, all studied with plain X-rays, 60% with CT and myelo-CT, and 40% with MR. We consider the classification and grading of these malformations, clinical, neuroradiological patterns, and indications for surgery. In the light of our findings and of the published data MR emerges as the key investigation. Only in a few cases of great anatomical complexity is it now necessary to perform CT and myelo-CT as well. A case in point is when the conus and thickened filum terminale are inextricably bound together and can no longer be considered separate structures. We propose the term "neurofibrous structure" to define the conus-thickened-filum-terminale unit when these structure are no longer distinguishable.