Morphological evaluation for neuronal maturation in anencephaly and encephalocele in human neonates. A proposal of reclassification of cephalic dysraphism.

The developmental pathogenesis of cranium bifidum and exencephaly, as well as other forms of the dysraphic state, remains unresolved. The process of neuronal maturation under such conditions is the major definitive factor for functional prognosis and may be the key to the embryopathogenesis. The neuronal maturation processes in cranium bifidum and anencephaly were analyzed in both human neonatal autopsy and surgical specimens, utilizing the technique of immunohistochemical morphological analysis. The results suggest that anencephaly is a form of neuroschisis, a defect in which the neuronal developmental process arrests and results in dys- or rather aplastic cortical architecture. In contrast, although the cortical architecture is often distorted, neuronal maturation in cases of cranium bifidum cysticum is primarily complete, demonstrating normal cerebral cortical layers and NSE positive neural elements. In conclusion, it is strongly suggested that anencephaly is the most severe form of cranium bifidum, as is myeloschisis in spina bifida, without supportable neuronal maturation. Recognizing these points in the developmental stages with regard to the degree of neuronal maturation, a reclassification of cephalic dysraphism is proposed. The embryopathogenetic and epidemiologic aspects of this proposal of reclassification are discussed.