Development of the Fetal Vermis: New Biometry Reference Data and Comparison of 3 Diagnostic Modalities-3D Ultrasound, 2D Ultrasound, and MR Imaging

Normal biometry of the fetal posterior fossa rules out most major anomalies of the cerebellum and vermis. Our aim was to provide new reference data of the fetal vermis in 4 biometric parameters by using 3 imaging modalities, 2D ultrasound, 3D ultrasound, and MR imaging, and to assess the relation among these modalities. A retrospective study was conducted between June 2011 and June 2013. Three different imaging modalities were used to measure vermis biometry: 2D ultrasound, 3D ultrasound, and MR imaging. The vermian parameters evaluated were the maximum superoinferior diameter, maximum anteroposterior diameter, the perimeter, and the surface area. Statistical analysis was performed to calculate centiles for gestational age and to assess the agreement among the 3 imaging modalities. The number of fetuses in the study group was 193, 172, and 151 for 2D ultrasound, 3D ultrasound, and MR imaging, respectively. The mean and median gestational ages were 29.1 weeks, 29.5 weeks (range, 21-35 weeks); 28.2 weeks, 29.05 weeks (range, 21-35 weeks); and 32.1 weeks, 32.6 weeks (range, 27-35 weeks) for 2D ultrasound, 3D ultrasound, and MR imaging, respectively. In all 3 modalities, the biometric measurements of the vermis have shown a linear growth with gestational age. For all 4 biometric parameters, the lowest results were those measured by MR imaging, while the highest results were measured by 3D ultrasound. The inter- and intraobserver agreement was excellent for all measures and all imaging modalities. Limits of agreement were considered acceptable for clinical purposes for all parameters, with excellent or substantial agreement defined by the intraclass correlation coefficient. Imaging technique-specific reference data should be used for the assessment of the fetal vermis in pregnanc

Fetal thymus volume estimation by virtual organ computer-aided analysis in normal pregnancies

The thymus has a pyramidal shape, which is best shown in coronal planes. The aim of this study was to evaluate the potential of virtual organ computer-aided analysis to estimate fetal thymus volume in normal pregnancies. Three-dimensional volume data sets from the axial upper mediastinal section were acquired from 37 normal pregnancies between 12 and 35 weeks' gestation. Thymus volume was calculated by virtual organ computer-aided analysis by 2 separate examiners. In 12 cases, volumes were also acquired with 4-dimensional sonography and spatiotemporal image correlation software to assess the variability in thymus size between the systolic and diastolic periods of fetal heart motion. Linear regression analysis was used to assess the relationship between the fetal thymus volume and gestational age. Paired Student t tests were used to evaluate both the level of agreement for interobserver and intraobserver variability and the difference between diastolic and systolic thymus volumes. Identification of the borders of the thymus and calculation of its volume were successful in 28 patients (77.7%). Statistically significant linear growth of the thymus during pregnancy, from 12 to 35 weeks, was found. The growth coefficient for each gestational age was 0.43 (95% confidence interval, 0.355 to 0.504; P < .001). The difference in thymus size between systole and diastole was minor (0.0798 cm(3); 95% confidence interval, -0.044 to 0.203 cm(3)). Interobserver and intraobserver variability was not statistically significant. Although the thymus has a complex shape, it was possible to determine its borders and to calculate its volume by virtual organ computer-aided analysis in 77.7% of cases. Linear growth during pregnancy was found, and the minor changes during systole and diastole could be explained by condensation of the soft tissue of the thymus secondary to cardiac activity