OP04.04: First‐trimester assessment of the nasal bones using the retronasal triangle view: a three‐dimensional sonographic study

Abstract

To evaluate a new technique for identifying the nasal bones (NBs) using the retronasal triangle (RNT) view, i.e., the coronal plane at which the palate and frontal processes of the maxilla are simultaneously visualized. Three-dimensional (3D) volumes were acquired from women undergoing first-trimester sonographic screening for aneuploidy by two accredited operators. Those datasets in which the fetal face was clearly identified were selected for off-line analysis by two other observers who were unaware of the final sonographic findings. The NBs were classified as both present, only one present (right or left), or absent according to the presence or absence of two small paired echogenic linear structures crowning the top of the RNT as determined by 3D navigation in the sagittal and coronal planes. Additional 3D datasets involving a subset of four first-trimester fetuses with absent NBs were also analyzed retrospectively and included randomly in the study group. A total of 103 3D datasets were analyzed, of which 86% were obtained transabdominally and 14% transvaginally. The NBs were classified as present in 99 (96%) of the cases and absent in four (4%), with complete agreement between observers in both the sagittal and coronal planes (Kappa coefficient = 1). Discrimination between the right and left NBs was possible in 88% and 89% for observer A, and 95% and 96% for observer B by assessing the sagittal and coronal views, respectively (right NB, Kappa = 0.90, 95% CI 0.79–1; left NB, Kappa = 0.85, 95% CI 0.6–0.99). The NBs were not identified with 3D sonography in any of the four trisomy 21 fetuses with absent nasal bones. This study demonstrates that the NBs can be identified as paired echogenic structures located at the top the RNT. This coronal view of the fetal face offers the possibility of screening for the presence or absence of the NBs, especially when the standard mid-sagittal views of the fetal face are suboptimal due to fetal or maternal factors.