[Prenatal diagnosis of anomalies of the corpus callosum with ultrasound: the echographist's point of view].

Ultrasonography can identify agenesis of the corpus callosum (excluding holoprosencephaly which an be detected earlier on) in the second trimester of pregnancy (18-20 weeks gestation). Diagnosis of corpus callosum agenesis is difficult but is important as a risk factor for neurological or genetic malformations. The characteristic signs suggestive of corpus callosum agenesis are: moderate distension of the occipital ventricle and the ventricular communications; absence of the spectrum giving rise to an upward displacement of the third ventricle shown in the anterior coronal section (especially in transvaginal ultrasonography); radial position of the fissures on the internal side of the cerebral hemisphere seen on the sagittal section; the absence in color coded Doppler of the pericallosal artery normally characterised by a semicircular vessel observable on the median sagittal section. At present, color coded Doppler should give the diagnosis of corpus callosum agenesis. MRI can provide further information especially in case of late detection around 28-30 weeks gestation as is most frequently the case. The development of 3D echographic imaging should allow an even more sophisticated approach to this diagnosis giving even more precise prognosis. Isolated corpus callosum agenesis is compatible with normal intellectual development an raises an important problem with regard to pregnancy continuation and infant development. Each individual case should be discussed during the pluridisciplinary prenatal diagnostic discussion.