Three-dimensional ultrasound in the evaluation of fetal head and spine anomalies

To test the application of three-dimensional (3-D) ultrasound for the antenatal diagnosis of fetal head and spinal anomalies.

Twenty-five fetuses with head or spinal anomalies and ranging in gestational age from 16 to 33 weeks were studied prospectively: 11 with a control nervous system anomaly (neural tube defect [n = 4], encephalocele [n = 2], hydrocephalus [n = 4], and anencephaly [n = 1]), 13 fetuses with a family history or suspicion of cleft lip or palate, and one with a cloverleaf skull malformation. A volume scan was performed after the two-dimensional examination was complete. The mechanical transducer scans up to 40 degrees in less than 4 seconds, acquiring the data for a pyramid-shaped tissue volume. Three matched and dynamically linked images representing the X, Y, and Z planes are displayed simultaneously. When one image is manipulated, the remaining images are updated automatically to maintain a 90 degrees difference. After the ideal three orthogonal planes are identified, a 3-D image can be reconstructed. A variable number of scan images are possible, depending on the volume size and the data acquisition time. Processing time for the reconstruction depends on volume size, the number of scan images included, and the degrees of rotation of the final image.

The three orthogonal planes proved most helpful delineating the exact nature and anatomic level of the defect. No examination was delayed or required repetition because of suboptimal fetal positioning. The enhanced confidence achieved by our being able to delineate the precise anatomic level and extent of the defect improved patient counseling. The 3-D reconstructions clarified and documented the true magnitude of the defects and on occasion allowed a diagnosis not possible by either two-dimensional or nonreconstructed 3-D imaging.

Our experience with 3-D ultrasound suggests that it is an advance in high-quality ultrasound. Its greatest advantage is that it allows the user to view simultaneously the three orthogonal planes.