Short-limb skeletal dysplasias: evaluation of the fetal spine with sonography and radiography.

Sonograms and radiographs of the lumbar spine in 51 fetuses and neonates with thanatophoric dwarfism, achondroplasia, and osteogenesis imperfecta type II were retrospectively evaluated. Study data included 27 prenatal and 27 neonatal sonograms and radiographs in 40 fetuses and neonates and 11 cases described in the radiology literature. To precisely compare the sonographic and radiographic appearances of platyspondyly in dysplasia, a simple vertebral ratio was obtained from measurement of vertebral interspace and vertebral body height. Normal ranges were obtained from sonograms in 125 normal fetuses and from radiographs in 55 normal fetuses. The severe platyspondyly of thanatophoric dysplasia and the milder platyspondyly of achondroplasia were detected by about 20 menstrual weeks. The vertebral bodies appeared slightly larger on sonograms than on radiographs in both normal fetuses and fetuses with dysplasia.