ABSTRACT
Figure 5.1 Normal structure outside the cerebral hemispheres. Outside the hemispheres, the subarachnoid space is normally observed. Outside the subarachnoid space, dura mater, cranial bone and the scalp cover the brain. SSS, superior sagittal sinus
strate the obliterated subarachnoid space and the dangling choroid plexus in the case of hydrocephalus (Figure 5.3). In contrast, the subarachnoid space and choroid plexus are well preserved in cases of ventriculomegaly 1 (Figure 5.4). It is difficult to evaluate obliterated subarachnoid space by the transabdominal approach which may not accurately differentiate hydrocephalus with increased intracranial pressure from ventriculomegaly without pressure. Therefore; it is suggested that the evaluation of fetuses with enlarged ventricles should be evaluated in the parasagittal and coronal views by the transvaginal way or three-dimensional multiplanar analysis. Figures 5.5-5.9 show sonographic images of hydrocephalus from early to late gestation. In early pregnancy, the subarachnoid space is not depicted even in normal fetuses. However, the choroid plexus is dangling and deviates toward the occipital portion
Figure 5.2 Subarachnoid space in a normal fetus. The subarachnoid space (SAS), which is demonstrated around the cerebral hemispheres is preserved during pregnancy. Right, graph shows the width change of subarachnoid space and the thickness of the cerebrum during a normal pregnancy
Figure 5.3 Ultrasound images of fetal hydrocephalus at 34 weeks of gestation. Left, coronal image. The subarachnoid space is obliterated. Right, sagittal image. A dangling choroid plexus is demonstrated (arrow)
Figure 5.4 Ultrasound images of ventriculomegaly. Enlarged ventricles exist but the subarachnoid space (arrowheads) is well preserved and there is no dangling choroid plexus, which indicates normal intercranial pressure. This condition should be differentiated from hydrocephalus
Figure 5.5 Early hydrocephalus at 10-12 weeks of gestation. Upper left and middle, axial images at 10 weeks. Choroid plexus is replaced
backwards in the ventricles and marked intraventricular fluid collection is demonstrated. Upper right, sagittal image at 12 weeks. The fetal head is enlarged and frontal bossing is conspicuous. Lower, external appearance of the head and face in an aborted fetus at 14 weeks. Images and photographs courtesy of Dr T.Murakoshi
Figure 5.6 Three-dimensional orthogonal views of hydrocephalus at 16 weeks of gestation. Upper left; coronal image; upper right, sagittal image; lower; axial image. This case was complicated by myelomeningocele. The subarachnoid space is already obliterated and a dangling choroid plexus is seen
Figure 5.7 Three-dimensional orthogonal views of hydrocephalus at 18 weeks of gestation. Upper left, coronal image; upper right, sagittal image; lower, axial image. The subarachnoid space is already obliterated and a dangling choroid plexus is seen
Figure 5.8 Hydrocephalus with third ventriculomegaly at 19 weeks of gestation. Upper left, sagittal ultrasound image; upper right, axial
image. Mild enlargement of the third ventricle is demonstrated (arrowheads). Lower left, anterior coronal image of hydrocephalus. The septum pellucidum is intact. Lower right, parasagittal image. Note the obliterated subarachnoid space and dangling choroid plexus
Figure 5.9 Ultrasound images of hydrocephalus at 34 weeks of gestation. Upper, serial coronal images. The septum pellucidum was destroyed, perhaps due to enlargement of the bilateral ventricles, and both ventricles were fused. A dangling choroid plexus is seen. Lower, parasagittal and sagittal images. A dangling choroid plexus and obliterated subarachnoid space are seen
of the lateral ventricles in a case of hydrocephalus as early as 10 weeks of gestation (Figure 5.5). Under normal conditions from the beginning of the second trimester, the subarachnoid space may be visible. The obliterated subarachnoid space and dangling choroid plexus are conspicuous (Figures 5.6-5.8). In some cases with hydrocephalus, the septum pellucidum is destroyed and both ventricles are fused together (Figure 5.9). This condition should be differentiated from the lobar type of holoprosencephaly. Furthermore, intracranial venous blood flow may be related to increased intracranial pressure. In normal fetuses, blood flow waveforms of dural sinuses, such as the superior sagittal sinus, vein of Galen and straight sinus have a pulsatile pattern 2 (see Chapter 4, Figure 4.26). However, in cases with progressive hydrocephalus, normal pulsation disappears and blood flow waveforms develop a flat pattern 2 (Figure 5.10). In cases with progressive hydrocephalus, there may be seven stages of progression (Figure 5.11):
(1) Increased fluid collection in the lateral ventricles;
(2) Increased intracranial pressure; (3) Dangling choroid plexus; (4) Disappearance of subarachnoid space; (5) Excessive extension of the dura and superior sagittal sinus; (6) Disappearance of venous pulsation; (7) Enlarged skull.
