Pathogenesis of diastematomyelia and spina bifida.

Three cases of spina bifida (SB) associated with diastematomyelia (DM) are described and possible differences in pathogenesis are discussed. The frequent simultaneous occurrence of both malformations and the possibility that the cord can be split above, at the level of or below the SB indicate a common pathogenesis for SB and DM. Splitting of the cord symmetrically, asymmetrically, bilateraly or even antero-posteriorly can be explained only by the existence of a destructive phenomenon which is responsible for the bifurcation of the neural tube or its anlage. The existence of such a phenomenon indicates that myelocele can develop due to re-opening of a previously closed neural tube. Meningocele may be a manifestation of early embryonic antero-posterior DM in which the anterior tubule develops into an almost normal spinal cord, whereas the posterior tubule provides the wall of the cystic sac of meningocele in which most or all the neural tissue undergoes fibrous replacement.