[Epidemiological survey of central nervous system anomalies and the implications of teratogens].

One of the aims of epidemiologic surveillance is to assess the role of environmental factors acting during pregnancy (teratogens) in abnormal development of the nervous system. The data of Eurocat, a european system of congenital anomaly surveillance, was analysed and evaluated. Great geographical variation is observed in the prevalence of neural tube defects. Geographical variation in the prevalence of microcephaly, hydrocephaly and holoprosencephaly, may be related to problems of definition, validation and precision of diagnosis. A better definition of the unit of surveillance is required for anomalies where phenotypic heterogeneity is linked to aetiologic heterogeneity (such as neural tube defects) and for anomalies which range from minor to major forms (such as microcephaly). The strengths and deficiencies of the surveillance system for central nervous system anomalies are revealed by its performance in the evaluation of the Chernobyl accident.