P13.11: Normal range of fetal intracranial translucency (IT) at 11.0 to 13.6 weeks of gestation in a Polish population

Abstract

Objectives: Size of posterior fossa (PF) is primary feature in the diagnostic algorithm of PF malformations. This study was designed to provide nomograms of the sonographic parameters of PF morphometry in median plane of fetal head. Methods: Three dimensional sonographic volumes of 348 fetal heads in 15–35 gestational weeks were retrospectively studied using multiplanar display in 4D-View application. All patients had low risk, singleton pregnancy, and delivered healthy babies. All examinations were performed by single sonographer (L.Z.). All sonographic volumes were obtained above fetal vertex by sagittal acquisition using transabdominal or transvaginal probe. Borders of PF were defined from clivus to tentorium and from occipital bone to upper tectal plate margin. The measured parameters were: Posterior Fossa Area (PFA), Posterior Fossa Perimeter (PFP). Measurements were performed in the median head plane, by a single observer (P.C.). Based on these measurements we determined the relationship of these parameters to gestational age. Results: From the 348 examinations that were initially included, 282 were selected according to technical visibility. We found a linear growth pattern of PFA and PFP with r = 0.97 for each parameter. Percentiles were calculated for each parameter according to gestational week. The total feasibility rate of our parameters was 81%. The intra-observer variation was 4.5% ± 2.3% for PFA and 2.1% ± 1.2% for PFP. Conclusions: In this study we found a linear growth pattern of the fetal PFA and PFP and created their percentiles along gestational weeks. Our data may be useful in the diagnosis of the anomalies characterized by abnormal posterior fossa size, like Dandy-Walker malformation, Arnold-Chiari malformation and PF arachnoid cyst.