Ultrasound visualization of the central nervous system during embryonic and fetal periods: Neurosonoembryology utilizing multiple three-dimensional transvaginal ultrasound technology.

OBJECTIVE

To study the ultrasonographic features of the central nervous system (CNS) in normally developing embryos and fetuses with a crown-rump length (CRL) of 10-84 mm, utilizing a high-frequency transvaginal probe in conjunction with various three-dimensional (3D) imaging modes.

METHODS

From January 2020 to February 2021, 210 normally developing embryos and fetuses in early pregnancy were enrolled and classified based on their gestational age. A high-frequency transvaginal transducer was used to perform 2D and 3D ultrasounds, and the 3D images were saved. These images were then processed using multiple 3D technologies, such as HD live silhouette, OmniView, and TUI. Additionally, the circumference of the vermis was measured through the posterior fontanelle.

RESULTS

Beginning at the 10 mm CRL stage of embryonic development, high-frequency transvaginal 3D ultrasound imaging was able to clearly visualize the prosencephalon, mesencephalon, and rhombencephalon. Notable changes were observed in the rhombencephalon during the 16-22 mm CRL stage, including the visualization of the pontine flexure and cerebellar primordium. At 23-40 mm CRL, there was a distinct pontine flexure, and the developing cerebellum, the fourth ventricle, and choroid plexus of the fourth ventricle (4th VCP) could be observed. The roof of the rhombencephalon was partitioned by the 4th VCP into the anterior membranous area (AMA) located rostrally and the posterior membranous area situated caudally. Additionally, the original Blake's pouch was identifiable. Among fetuses measuring 41-84 mm CRL, the AMA progressively decreased in size as the vermis developed. From the mid-sagittal view, the orientation of the 4th VCP seemed to shift from being perpendicular to the neural tube's long axis to being parallel to it. Furthermore, there was a significant correlation between CRL and vermis circumference.

CONCLUSION

Using three-dimensional transvaginal ultrasound scanning, detailed visualization of the morphological changes in the CNS during normal embryonic development from 7 to 13+6  weeks is possible. This technology can aid in accurately characterizing the embryonic origin of the CNS.