3-DIMENSIONAL ULTRASOUND IN THE EVALUATION OF FETAL HEAD AND SPINE ANOMALIES

Objective: To test the application of three-dimensional (3-D) ultrasou nd for the antenatal diagnosis of fetal head and spinal anomalies. Met hods: Twenty-five fetuses with head or spinal anomalies and ranging in gestational age from 16 to 33 weeks were studied prospectively: 11 wi th a central nervous system anomaly (neural tube defect [n = 4], encep halocele [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 tr ansducer 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 simul taneously. When one image is manipulated, the remaining images are upd ated automatically to maintain a 90 degrees difference. After the idea l three orthogonal planes are identified a 3-D image Fan be reconstruc ted. A variable number of scan images are possible, depending on the v olume size and the data. acquisition time. Processing time for the rec onstruction depends on volume size, the number of scan images included , and the degrees of rotation of the final image. Results: The three o rthogonal 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 confi dence achieved by our being able to delineate the precise anatomic lev el. and extent of the defect improved patient counseling. The 3-D reco nstructions clarified and documented the true magnitude of the defects and on occasion allowed a diagnosis not possible by either two-dimens ional or nonreconstructed 3-D imaging. Conclusion: our experience with 3-D ultrasound suggests that it is an advance in high-quality ultraso und. its greatest advantage is that it allows the user to view simulta neously the three orthogonal planes.