Three-dimensional transvaginal neurosonography of the fetal brain: 'navigating' in the volume scan

Fetal neuroscan by ultrasound has gained in importance over recent years. Two-dimensional (2D) transvaginal sonography was an important step in understanding the constantly changing and developing fetal brain. The objective of this article is to describe the use of three-dimensional ultrasound of the fetal brain enhanced by the transvaginal transfontanelle scanning technique.

Thirty-four pregnant patients were referred to us because of a history of brain anomaly or suspected brain pathology. The fetuses were scanned transvaginally. Two-dimensional as well as three-dimensional (3D) images were generated. The volumes obtained by the 3D-ultrasound machine were displayed in the three conventional orthogonal planes (coronal, sagittal and axial).

Of the 34 fetuses 10 had normal brain anatomy and 24 had brain pathology. In all 34 cases the 2D images as well as the 3D volumes were of diagnostic quality and all three planes could be obtained. The axial sections could only be obtained by the 3D re-construction of the volume scans. The 2D images produced were acquired from a common point originating from the foot print of the transvaginal probe at the fetal anterior fontanelle or the sagittal suture, the sections 'radiate' from this point. Therefore, these sections are not parallel sections, but are oblique to each other. In contrast, the 3D volume could be examined using the classical parallel sections in all three orthogonal planes. The posterior fossa could be seen better if the footprint of the probe was placed over the posterior fontanelle or on the sagittal suture. The marker dot enabled a precise creation of anatomy and pathology. In the 'angio mode' it was possible to follow the anterior cerebral and pericallosal artery.

The 3D-ultrasound technology using the transvaginal approach is effective and practical to perform during fetal neuroscan. The ability to 'navigate' in the volume and the 'marker dot' enables exact location of normal structures and evaluation fetal brain pathology. The volume can be reviewed over and over again, can be mailed to an expert, could be shown to consultants (pediatric neurology and neurosurgeons) and used for teaching.