First-Trimester Assessment of the Nasal Bones Using the Retronasal Triangle View

Abstract

Objective. The purpose of this study was to evaluate a new sonographic technique for identifying the nasal bones using the retronasal triangle view, ie, the coronal plane at which the palate and frontal processes of the maxilla are simultaneously visualized. Methods. Three-dimensional (3D) volumes were acquired from women undergoing first-trimester sonographic screening for aneuploidy by 2 accredited operators. Those data sets in which the fetal face was clearly identified were selected for offline analysis by 2 other observers who were unaware of the sonographic or clinical findings. The nasal bones were classified as both present, only 1 present (right or left), or absent according to the presence or absence of 2 small paired echogenic linear structures at the upper tip of the retronasal triangle as determined by 3D navigation in the coronal plane and compared to those findings obtained by 3D navigation in the sagittal plane. Additional 3D data sets involving a subset of 4 first-trimester fetuses with trisomy 21 and absent nasal bones were also analyzed retrospectively and included randomly in the study group. Results. A total of 110 3D data sets were analyzed, of which 86% were obtained transabdominally and 14% transvaginally. The quality of nasal bone identification was classified subjectively by the observers as good in 67% of cases, fair in 29%, and poor in 4%. The nasal bones were classified as at least 1 present in 106 of the cases (96%) and absent in 4 (4%), with complete agreement between observers in both the sagittal and coronal planes (κ = 1). Discrimination between the right and left nasal bones was possible in 89% and 93% for observer A and in 96% and 96% for observer B by assessing the sagittal and coronal views, respectively (right nasal bone: κ = 0.90 [95% confidence interval (CI), 0.79-1]; left nasal bone: κ = 0.85 [95% CI, 0.60-0.99]). The nasal bones were not identified at the level of the retronasal triangle view in any of the fetuses with trisomy 21 and absent nasal bones. Conclusions. This study shows that the nasal bones can be confidently identified as paired echogenic structures located at the upper tip of the retronasal triangle. This coronal view of the fetal face offers the possibility of screening for the presence or absence of the nasal bones in the first trimester, especially when the standard midsagittal views of the fetal face are suboptimal because of fetal or maternal factors. Because both nasal bones can be evaluated simultaneously in the coronal plane, the retronasal triangle view may be advantageous over the conventional midsagittal view assessment, in which only 1 of the 2 nasal bones is evaluated.

Sensitivity of Nasal Bone as Aneuploidy Marker—First Trimester versus Second Trimester Assessment

“…Unilateral nasal bone often presents as absent nasal bone in midsagittal view [19]. This differentiation can easily be found in RNT view; where the nasal bones appear as two echogenic dots at the apex of triangle [15,19]. In the present series authors had three cases where the nasal bone was absent in the first trimester but appeared normal in the second trimester and hence the obtained FTS risk was not modified in these three cases.…”

“…The ossification pattern of nasal bone may be the presence of only one nasal bone or hypoplastic nasal bones or complete absence of nasal bone. Unilateral nasal bone often presents as absent nasal bone in midsagittal view [19]. This differentiation can easily be found in RNT view; where the nasal bones appear as two echogenic dots at the apex of triangle [15,19].…”

Clinical Significance of First-Trimester Screening of the Retronasal Triangle for Identification of Primary Cleft Palate

“…In fact, the detection rate for any fetal structural malformation in the first trimester only reaches a value in the range 0.7−4.7% [24]. Reports of CP in the first trimester are scarce [10,][11,26,27,28]. Syngelaki et al [25] demonstrated a 5% detection rate for facial cleft with non-chromosomal abnormalities at 11-13 weeks.…”

“…Indeed, the RNT may become an important sonographic landmark for several fetal anomalies as understanding and technology improves. Martinez-Ten et al [28] found the nasal bones could be confidently identified in the coronal plane as paired echogenic structures located at the upper tip of the RNT, which might be advantageous over a midsagittal assessment, in which only 1 of the 2 nasal bones can be evaluated. Sepulveda et al [31] found the disappearance of the space between the left and right mandibular bodies in the RNT and this finding may help to diagnose micrognathia deformity in the first-trimester.…”

AIUM Practice Parameter for the Performance of Detailed Diagnostic Obstetric Ultrasound Examinations Between 12 Weeks 0 Days and 13 Weeks 6 Days

“…98 The retronasal triangle can be used to identify the paired nasal bones, premaxillary processes, primary palate, and the mandible. [99][100][101][102] The absence of the mandibular gap raises a concern for micrognathia. 101 A sweep of the coronal planes can be used to demonstrate the orbits, lenses, and integrity of the upper lip.…”