OBJECTIVE: To establish normal reference ranges for the depth of the insula and Sylvian (SF), parieto-occipital (POF) and calcarine (CF) fissures on prenatal ultrasound between 19 and 30 weeks of gestation. METHODS: This was a prospective study of 15 consecutive normal fetuses per gestational week between 19 + 0 and 30 + 6 weeks. We measured the depth of the insula and SF in a standard transventricular axial plane of the fetal head; the depth of the POF in a plane above and parallel to that used for the insula; and the depth of the CF in a coronal view of the posterior fossa. All measurements were done transabdominally during the routine second- or third-trimester examination. Reproducibility for each of the parameters was assessed by two operators using stored images from 30 cases. RESULTS: The depth of the four structures increased with increasing gestational age. The insula and SF could be seen in all cases from 19 weeks onwards, while the POF and CF could be identified in 93.3% and 6.6% of cases, respectively, at 19 weeks. From 20 weeks onwards, the POF could be seen in all examinations, as could the CF from 24 weeks. Intra- and interobserver reproducibility analysis showed good results. CONCLUSIONS: Assessment of the insula, SF, POF and CF is feasible during prenatal ultrasound examination using standard views of the fetal head. Since the normal ranges increase with gestational age, they could be used to estimate brain development. It is possible that this assessment might be incorporated into the neurosonogram to identify fetuses at risk of maturation disorders or as a complement to other standard evaluations.
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