Ultrasound and MR Imaging of Fetal Neural Tube Defects

Neural tube defects are among the most common congenital anomalies in the United States, the three major types being anencephaly, cephalocele, and spina bifida. By far, most spina bifida cases are myelomeningoceles. Ultrasound plays an important role in the detection and evaluation of these defects. Anencephaly has a characteristic appearance of lack of ossified skull above the orbits, and can be diagnosed in the late first trimester. The spinal defect and brain findings associated with myelomeningocele are well detected by ultrasound, typically in the second trimester. The underlying brain findings in cases of encephalocele are particularly important, and MR imaging is often helpful in these cases. Careful anatomic survey and karyotype analysis are helpful in counseling patients who have a prenatal diagnosis of these defects.