Ultrasound of the fetal spine.

The sonographic appearance of the fetal spine was studied using a dynamic section (real time) machine in 7000 pregnancies. The interpretation of the appearance was verified by the use of aborted fetuses and models in a water bath, and by clinical outcome. Twenty-nine cases of spina bifida occurred in the series, 12 with associated anencephaly, 17 with a spinal defect alone. Analysis of results by clinical outcome and ultrasonic examination of aborted abnormal fetuses show that cases with significant vertebral body and/or lateral mass abnormalities could be detected with good accuracy (91%) but those with only neural arch defects were not accurately detected, making the overall accuracy 79%. The spine is visualised in two longitudinal planes. The cranio-cervical junction is well shown in the dorsal sagittal plane, while the sacrum is identified by its characteristic curve in the sagittal plane and by its relation to the iliac bones in the coronal plane. Gaps in the lines representing the neural canal are produced by sonic shadows in the iliac bones and shoulders in the coronal planes and by the soft tissues of the extended neck in the sagittal plane. An oblique view of the gluteal region may mimic a soft tissue swelling. A third line between the two representing the neural canal is due to the transverse processes of the vertebrae.