Incomplete, false, and true diastematomyelia: radiological evaluation by air myelography and tomography.

Six cases of possible diastematomyelia studied by air myelography with tomography were thought to involve fibrous or bony septa, but in each case no septum was found. Surgical findings included prominent midline posterior fissures in the cord associated with fibrous bands, an unusual tentlike extension of the arachnoid over the spinal cord, and hemicords with no intervening septum. Recognition of an osseous septum on the plain film does not necessarily mean that the cord is completely divided by bone, as other structures derived from the mesoderm, such as fat or cartilage, may contribute to the septum. The importance of defining tethering of the cord posteriorly at the septum or conus level is stressed. Air myelography with appropriate projections appears to show posterior fixation of the cord to best advantage.