Cranial base and vertebral column in human anencephalic fetuses.

The purpose of the present study was to investigate the axial skeleton related to the notochord in human anencephalic fetuses in order to elucidate the pathogenesis. Fifteen second trimester fetuses were examined. The spine and the cranial base were dissected and radiographed. Comparison with normal fetuses was performed. Two patterns of abnormal ossification were seen. Anencephalic cases without cervical rachischisis (Groups I and II) differed markedly from cases with cervical rachischisis (Group III). Morphological characteristics, such as bilateral narrowing of the basilar part of the occipital bone combined with normal cranio-caudal dimension, were found in cases without cervical rachischisis. In these cases frontal clefting of vertebral corpora occurred. Caudocranial shortening of the basilar part of the occipital bone was found in cases with cervical rachischisis, where complete median clefting of vertebral corpora also occurred. Because the vertebral corpora and the basilar part of the occipital bone develop around the notochord, which interacts also in the process of neurulation, the defects might indicate a notochordal insufficiency. The study showed that when the initial closure of the neural groove failed, the skeletal deviations were more extensive. The study supports the hypothesis that the notochord is an important clue to an understanding of the pathogenesis in anencephaly.