Ultrasound of the fetal central nervous system.

Current ultrasound equipment allows the antenatal identification of many central nervous system anomalies from early gestation. In selected cases, special techniques (transvaginal sonography, three-dimensional ultrasound, colour Doppler) may enhance the diagnostic potential. Diagnostic accuracy, however, remains heavily dependent upon the expertise of the sonologist. Fetal ultrasound is effective in identifying neural tube defects, although alpha-fetoprotein screening seems to yield a greater sensitivity. The sensitivity in the diagnosis of central nervous system malformations other than neural tube defects remains unclear because of the ascertainment biases of the few large prospective studies that have been carried out so far. Magnetic resonance imaging may play a major role in the evaluation of cases with suboptimal ultrasound visualization, or when specific anomalies are suspected, such as intracranial haemorrhage or migrational disorders.