Prenatal diagnosis of neural tube defects: origin of midtrimester vertebral ossification centers as determined by sonographic water-bath studies.

A normal vertebral column was removed from a 17-week stillborn fetus and suspended in a water bath. The specimen was sequentially dissected, with spinous processes, transverse processes, and remaining neural arch removed. After dissection, each specimen was imaged by ultrasound in axial, sagittal, and coronal planes. The resultant images clearly demonstrated the origin of the three ossification centers as one at each lamina-pedicle junction and one in the vertebral body. Corollary X-ray studies confirmed the ultrasound findings and, in a case of open spina bifida, demonstrated the superiority of sonography for making this diagnosis.