**2.1. The spine**

may be recognized. The *transcerebellar* plane is obtained through the posterior fontanelle. The occipital horns of the LV and IEF are seen, also the cerebellar hemispheres and the

**Figure 7.** The transfrontal plane (the frontal-2), the transcaudate plane (mid-coronal-1), the transthalamic plane (mid-

In the *midsagittal* (median) plane, all components of the CC (rostrum, genu, body, splenium) may be seen. Also, the CSP, the brain stem, pons, vermis, and posterior fossa. The parasagittal planes (right and left) depict the entire LV, the choroid plexus, the periventricular tissue, and

The antero-posterior planes are displayed in **Figures 8** and **9**.

**Figure 8.** The sagittal plane. The corpus callosum is highlighted in the middle image.

coronal-2), and the transcerebellar plane (occipital-1 and 2).

48 Congenital Anomalies - From the Embryo to the Neonate

vermis.

the cortex.

In the sagittal and parasagittal planes, the ossification centers of the vertebral body and posterior arches form two parallel lines that converge in the sacrum, in the prone position of the fetus. Efforts must be made to demonstrate the integrity of the overlying skin.

In the second and third trimesters, these planes allow imaging of the spinal canal and of the spinal cord within it. The conus medullaris is usually found at the level of L2–L3 vertebrae (**Figure 10**).

In transverse planes or axial planes, the vertebrae have different shapes at different levels [1]. Fetal thoracic and lumbar vertebrae have a triangular shape, the first cervical vertebrae are quadrangular in shape, and sacral vertebrae are flat.

The normalcy of the vertebrae and ribs' arches may be very easily demonstrated in the coronal plane, using the 3D technique, skeletal mode. Both can be readily numbered (**Figure 11**).

In the prenatal scanning, many normal and abnormal structures may vary and evolve intensively. Thus, using descriptive terms is advisable. The observer may use a thorough detailed depiction of the visualized structures and features, may note the absent normal structure/ structures, and may signalize an abnormal structure. This approach is preferred to issuing a specific diagnosis.

**Figure 10.** The imaging of the spine and the distal region of the spinal canal. Axial thoracic vertebrae.

Establishing its class of severity is based on the width of the atrium of the lateral ventricle measurement: ventriculomegaly is considered to be mild when the atrial width is 10–12 mm,

Fetal Central Nervous System Abnormalities http://dx.doi.org/10.5772/intechopen.76208 51

Yet, this is usually a second- and third-trimester diagnosis. The prevalence of mild ventriculomegaly, based on current criteria, is estimated to be around 0.7% [12]. The finding of ventriculomegaly should trigger a thorough analysis of the fetal brain to investigate all associations (malformative, clastic, tumoral, and syndromic). If no underlying pathophysiology and etiology are found, ventriculomegaly is referred to as "isolated." Melchiorre et al. [13] demonstrated the particularly difficult counseling in such cases. Aqueductal stenosis is the most common cause of ventriculomegaly and its extreme form—fetal hydrocephalus. Published studies of neonates with aqueductal stenosis have noted variable outcomes, with normal

**Figure 15.** Twin monochorionic diamniotic pregnancy, with discordant major SNC anomaly: severe ventriculomegaly due to aqueductal stenosis. The images display comparatively the same planes: the transthalamic (a) and transcerebellar plane (b), the fetal profile (c) at 17 WA. The transthalamic plane at 25 WA (d). The long-term evolution of fetus B was

moderate between12 and 15 mm, and severe if larger than 15 mm.

development seen in 24–86% of cases [14] (**Figures 13**–**15**).

favorable (after ventriculo-peritoneal shunt).

In rare cases, ventriculomegaly is accessible in early pregnancy (**Figure 12**).

**Figure 14.** Different cases of unilateral borderline isolate ventriculomegaly, symmetric, and asymmetric.

**Figure 11.** Imaging the spine in the coronal plane. In left image, a supernumerary lumbar rib case is shown.
