Diastematomyelia and spina bifida can be caused by the intraspinal grafting of somites in early avian embryos.

OBJECTIVE In this experimental study, an embryological model was created to reproduce diastematomyelia and spina bifida and to investigate new aspects of the origin of spinal cord malformations. METHODS A somite was implanted from a donor quail embryo into the neural tube of a 2-day-old chick embryo. The somite was chosen because the septum that characteristically separates the two hemicords consists exclusively of mesodermal derivatives. RESULTS After 2 days of reincubation, diastematomyelia, spina bifida, or a normal embryo without a graft was observed. If the graft persisted in the neural tube, it formed a septum between the floor and roof plates but never made contact with the lateral walls of the tube. Otherwise, the graft was extruded from the neural tube. In this case, the quail cells often were found in dorsal or dorsolateral positions in the surrounding tissue. Sometimes, the wall of the neural tube formed an extrusion in the direction of the eliminated graft. On many occasions, however, spina bifida aperta was produced and no quail cells could be found in the host. CONCLUSION The results suggest that diastematomyelia may be the result of abnormal mesodermal invasion of the neural tube. The development of a septum in the neural tube after implantation of a somite may mimic the process during spontaneous diastematomyelia formation, which could be the consequence of abnormal gastrulation, the process by which the two early germ layers of the blastodisc are converted into the three definitive germ layers.