Pattern of malformations in the axial skeleton in human trisomy 13 fetuses.

The purpose of this study was to analyse the development of the axial skeleton in human trisomy 13 fetuses and to define which fields in the axial skeleton are affected in this condition. We investigated nine human fetuses with trisomy 13 and gestational ages of 14-19 weeks. Whole body radiographs and radiographs of midsagittal tissue blocks of the cranial base and the spine were studied. In the youngest fetus, 14 w GA, no malformations were observed. In eight fetuses, 17-19 weeks GA, malformations occurred in the lumbosacral spine. In four fetuses additional malformations were observed in the thoracic spine. The study showed that there was a correspondence between the extent of malformation in the lumbosacral spine and the thoracic spine. When mild malformation occurred in the lumbosacral region, no malformation was observed in the thoracic region, whereas malformation was observed in the thoracic region when there was extensive malformation in the lumbosacral region. Malformations did not occur in the cervical spine or the basilar part of the occipital bone, but the postsphenoidal part of the sphenoid bone was small and irregular in the six cases where it could be examined. In seven fetuses there was malformation or agenesis of the nasal bone. This pattern of axial skeletal malformations in trisomy 13 fetuses was not described previously. Comparisons are made with previous studies of the fetal axial skeleton in trisomy 18 and trisomy 21, where the pattern of malformations was different. We reiterate our recommendation that axial skeletal radiography should be part of the postmortem examination of fetuses with suspected or verified chromosome abnormalities.