ABSTRACT
Figure 4.1 The fetal skull in early pregnancy. Two-dimensional ultrasound can demon-strate the fetal skull formation from an early stage. The most remarkable morphological change during early pregnancy is the metopic suture change. The V-shaped metopic suture between the
bilateral frontal bones at 12 weeks changes into a linear structure at around 17 weeks
Figure 4.2 The fetal cranial structure in early gestation (three-dimensional ultrasound images). Upper left, 12 weeks, from the oblique front. Upper middle, 13 weeks, from the back. Upper right, 15 weeks, from the top of the head. Lower left, 12 weeks, from the front. Lower right, 17 weeks, oblique position. The premature shapes of the cranial bones; sutures and fontanelles at 12-13 weeks gradually change their appearance to the neonatal cranial shape. AF, anterior fontanelle; PF, posterior fontanelle; ALF, anterolateral fontanelle; F; frontal bone; P, parietal bone; O, occipital bone; C, coronal suture; M, metopic suture; S, sagittal suture; L, lamboid suture
Figure 4.3 Suture width change during normal pregnancy. The change of suture width between 12 and 28 weeks of gestation. Sagittal suture is the widest suture. This fact indicates that transvaginal sonography is a reasonable way to approach the fetal brain
INTRACRANIAL STRUCTURE
As described in Chapter 2, the brain should be understood as a three-dimensional structure. Figures 4.4-4.9 show normal fetal brain images in the same cutting section at different gestational ages. By use of transvaginal three-dimensional sonography as des cribed in Chapter 3, serial tomographic images in the three orthogonal sections can be demonstrated. Figures 4.10-4.17 show serial parallel sectional images of normal fetuses in the sagittal, coronal and axial planes at 8, 11, 15, 19, 24, 27, 31 and 36 weeks of gestation. Gyral formation is observed from approximately 26-28 weeks of gestation by
Figure 4.4 Axial sections at 18 and 33 weeks of gestation
Figure 4.5 Sagittal sections at 19, 26 and 35 weeks of gestation
Figure 4.6 Parasagittal sections at 15, 18, 27 and 34 weeks of gestation
Figure 4.7 Parasagittal sections at 28, 32 and 36 weeks of gestation
Figure 4.8 Anterior coronal sections at 18; 22, 21 and 38 weeks of gestation
Figure 4.9 Posterior coronal sections at 19, 26 and 32 weeks of gestation
Figure 4.10 Normal intracranial structure at 8 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial
sections from above. The premature sonolucent ventricular system is visible
Figure 4.11 Normal intracranial structure at 11 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above
Figure 4.12 Normal intracranial structure at 15 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above
Figure 4.13 Normal intracranial structure at 19 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above
Figure 4.14 Normal intracranial structure at 24 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above
Figure 4.15 Normal intracranial structure at 27 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above
Figure 4.16 Normal intracranial structure at 31 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above
Figure 4.17 Normal intracranial structure at 36 weeks of gestation in parallel cutting slices of three orthogonal views; sagittal, coronal and axial sections from above. Note the gyral formation in the late pregnancy
sonography. After 30 weeks, sulci and gyri are well demonstrated as shown in Figure 4.18. Isolated lateral ventricular asymmetry is often detected as the area difference between the left and right ventricles in fetuses during the latter half of pregnancy (Figure 4.19) or in neonates. In most cases, an asymmetry resolves spontaneously during pregnancy or after birth and generally has no clinical significance and may be a normal variation. Ventricular asymmetry should be differentiated from the initial sign of progressive unilateral hydrocephalus or a rare developmental malformation such as unilateral megalencephaly.
