Histological features of axial structures during embryonic and fetal stages of human craniorachischisis.

Histological characteristics of developing axial structures in human conceptuses with craniorachischisis were investigated during the embryonic and fetal periods and compared with normal samples. The morphological relationship of the notochord to the axial skeleton and neural tube was analyzed along cervical and thoracic vertebral segments using serial paraffin sections. The embryonic stage of malformed conceptuses disclosed a correlated affection of the notochord and vertebral column, as well as the overlying central nervous system. The degree of histological changes within the spinal cord depended on the level of the vertebral axis examined: completely unorganized nervous tissue was overlying cervical and upper thoracic vertebrae, while more caudally it resembled a normal spinal cord. During the fetal period the histological disturbances of all axial structures were more pronounced. Extensive notochordal branching was associated with the malformed formation and ossification of the vertebral column. At this stage we found no correlation of histological changes between the spinal cord and the mesodermally derived structures (notochord, vertebral column) along the cranio-caudal body extent, as neural tissue had completely transformed into area cerebrovasculosa. We speculate that our histological observations could be the result of primary affection of mesodermal structures during very early stages of development. Divergence in histological findings within axial structures between the embryonic and fetal periods support recent mutational investigations on animals.