Pattern of malformations in the axial skeleton in human trisomy 21 fetuses.

In the present study, we analyzed the development of the axial skeleton in human trisomy 21 fetuses and defined the fields in the axial skeleton affected in this form of aneuploidy. We investigated 31 human fetuses with trisomy 21, gestational ages 12-24 weeks, on the basis of radiographs of midsagittal tissue blocks of the axial skeleton, comprising the cranial base and the spine. Malformation or agenesis of the nasal bone was present in 19 of 31 fetuses. Nineteen cases had vertebral malformations. Fourteen fetuses had malformations in the cervical region, four in the thoracic and eight in the lumbosacral region. In 1 of 31 fetuses, malformation was seen in the basilar part of the occipital bone. The basisphenoid component appeared scallop-shaped in 30 cases. The pattern of axial skeletal malformations in trisomy 21 fetuses recorded here has not been described previously. Comparison is made with our recent study of trisomy 18, where the pattern of axial skeletal malformations was quite different. It is recommended that axial skeletal radiography should be part of the autopsy of fetuses where chromosome abnormalities are known or suspected.