Neural tube defects in the parietal region of human embryos: failure to close or closure-reopening?

This is a follow-up study to earlier investigations on neural tube defects (NTD) in the Kyoto collection of human embryos. It includes an extensive examination of abnormal embryos which have been photographed and serially sectioned following routine histological preparation. Two new types of NTD are described in the parietal region (the roof of the third ventricle) which had previously been overlooked. These anomalies were found most commonly in embryos at the developmental period. Carnegie stage [CS] 16-23 (embryonic days 38-52). Hypotheses are advanced regarding the genesis of NTD and whether encephaloceles and NTD are part of a spectrum of malformation. This study also reinforces evidence that the occurrence of NTD is significantly higher in the embryonic period than at birth. Animal studies, using the guinea-pig are discussed with regard to the investigation of hypotheses put forward to explain the genesis of NTD.