Duplication of the spinal cord: a discussion of the possible embryogenesis of diplomyelia.

The possible embryogenesis of diplomyelia is discussed in the context of the current understanding of neurulation. The mechanisms of normal development of the neural tube differ from one region to another, so the initial step in development of diplomyelia will probably depend on the location of the lesion. In the cranial portion of the neural tube, abnormal folding of the neural plate is most likely to be responsible for the formation of supernumerary lumina. In the intermediate transitional region, the neural plate diminishes as the contribution from the end bud increases, so errors might originate in either or both of these structures. In the caudal region of the embryo, the neural tube is established by canalization of the solid medullary cord, so diplomyelia in this region is most likely to stem from faulty canalization. Once the sub-populations of neural cells have been established, their subsequent physical separation appears to be due to changes in the region between the adjacent lumina, for example enlargement of intercellular spaces and degeneration of neural cells.