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[Sonographic abnormalities of the fetal CNS in the second trimester screening--clarifications according to the new maternity directives].

Malformations of the central nervous system are among the most frequent congenital anomalies. At best, a qualified and standardised screening of the foetal brain is possible between the 18th and the 22nd week. The newly decided modification of the maternity directives envisages an extended screening upon request. This extended screening refers to the central nervous system and the representation of the ventricles, the evaluation of the head shape and the cerebellum and the back. The examination of the foetal brain should be carried out in a structured way. Three axial planes, the transventricular, the transthalamic and the transcerebellar planes, suffice to represent and measure all structures which are of importance for the screening. In case of ventricular anomalies, anomalies of the head shape, anomalies of the cerebellum and irregularities of the dorsal skin outlined in the second screening a further diagnostic procedure should be initiated. This diagnostic work-up should include a detailed neurosonography, a diagnostic evaluation of the organs and eventually further examination in the form of a caryotyping, determination of the infectology or a foetal MRI. The present article offers an overview of possible CNS abnormalities which could be recognised during the second screening according to the extended maternity directives and describes which differential diagnostics should be considered. In detail, anomalies of the head size (microcephaly, macrocephaly), of the head size (brachycephaly, dolichocephaly, cavities of the cranium, banana sign, etc.,), ventricular abnormalities, anomalies of the cerebellum (cerebellum hypoplasia, abnormal cerebellum shape) and abnormalities of the intermediate line and the intracerebral space requirements are discussed.