WS01‐03The posterior fossa: a useful landmark in the evaluation of the fetal ventriculomegaly

Abstract

ObjectiveThe objective of this study was to obtain a nomogram of the clivus‐suvraocciput angle as a basis for the diagnosis of Chiari II malformation in fetuses with ventriculomegaly.DesignA cross‐sectional study was undertaken on 310 normal pregnant women of 16–34 weeks' gestation. A mid‐sagittal section of the fetal skull was obtained and the angle between the clivus and the supraocciput was measured. 44 fetuses with ventriculomegaly due to different causes (13 Chiari II malformation, 12 dysgenesis of the corpus callosum, 7 aqueductal stenosis, 6 borderline ventriculomegaly, 3 Dandy‐Walker malformation, 2 porencephaly, 1 schizencephaly) were also included into the study and the values of the angle found in the pathological cases were compared with that found in the normal population.ResultsThe clivus‐supraocciput angle did not change during gestation and was almost constant with an average value of 79,3° ± 6°. All cases of Chiari II malformation showed a value below the 10th centile of our nomogram; all the remaining cases of ventriculomegaly showed normal values of the angle.ConclusionsThe evaluation of the posterior fossa and particularly the measurement of the clivus‐supraocciput angle is a useful parameter to differentiate the various causes of fetal ventriculomegaly and particularly to recognize Chiari II malformation. The measurement of the angle could be also useful to screen for spina bifida which is almost constantely associated to Chiari II malformation.