**2. Normal findings**

Some intracranial segments of CNS are seen on ultrasound *extremely early* in development, especially when using high-resolution probes and modern electronic tools. Although many features are indeed recognizable, the clinical utility of such studies is yet to be proven (**Figures 1**–**3**).

In the *late first trimester*, current guidelines recommend checking for present cranial bones, for normal midline falx, and for the presence of choroid plexus and filled ventricles [9]. The most recommended planes for assessing the head anatomy are the axial ones. In terms of spine assessment, the guidelines state that "longitudinal and axial views should be obtained to show normal vertebral alignment and integrity, and an attempt should be made to show intact overlying skin" [9] (**Figure 4**).

From the early *second trimester* onwards, the commendation is to obtain in standard assessment three standard axial planes (transventricular, transthalamic, and transcerebellar), and, if technically feasible, the fetal profile [10] (**Figures 5** and **6**).

inner edge (the "leading edge" technique), at the widest part of the skull, using a perpendicular angle to the midline falx. The HC is measured on the external contour. The cranial bones describe on axial planes a regular *ovoid* shape. The *midline* must be continuous, having no deviations, and the intracranial structures must be symmetrical, mirroring each other's half. Usually, the proximal hemisphere to the probe has a lower visibility, and only the distal one is described by the operator. On the *transthalamic plane*, the anatomic landmarks are (from anterior to posterior) the frontal horns of the lateral ventricles (LVs), the cavum septi pellucidi (CSP), located between

**Figure 1.** Dating ultrasound scan at 8 weeks of amenorrhea (WA) and 3 days (d). Volumetric ultrasound: sectional planes in the multiplanar mode (a). Subsequently, OmniView facility was used, the line mode (b, c, and d). The embryonic

Fetal Central Nervous System Abnormalities http://dx.doi.org/10.5772/intechopen.76208 45

central nervous primitive vesicles can be observed.

The measurements for fetal head *biometry* (the biparietal diameter—BPD and the head circumference—HC) are possible when using the transventricular (biventricular) and the transthalamic plane. In the most commonly used technique, the calipers are placed from the outer edge to the

anomalies of the central nervous system develop early, and nowadays, we have the tools to detect some conditions at 11–13 weeks [3–8] or even earlier. The first-trimester detection of CNS anomalies is probably the most important advance in modern sonoembriology. Later in

pregnancy, neurosonography is a powerful tool in diagnosing CNS pathology.

**3.** Neural tube defects (NTDs) (anencephaly, encephalocele, myelomeningocele)

**7.** Vascular abnormalities (hemorrhage, hematoma, dural fistula, aneurysms)

**4.** Cortical formation abnormalities (schizencephaly, lissencephaly, heterotopia, microcephaly)

**5.** Midline abnormalities (holoprosencephaly, complete/partial agenesis of corpus callosum

**6.** Posterior fossa abnormalities (mega cisterna magna, Blake's pouch cyst, Dandy-Walker or

**8.** Destructive lesions (hydranencephaly, tumors/mass lesions, cysts, periventricular leu-

Some intracranial segments of CNS are seen on ultrasound *extremely early* in development, especially when using high-resolution probes and modern electronic tools. Although many features are indeed recognizable, the clinical utility of such studies is yet to be proven

In the *late first trimester*, current guidelines recommend checking for present cranial bones, for normal midline falx, and for the presence of choroid plexus and filled ventricles [9]. The most recommended planes for assessing the head anatomy are the axial ones. In terms of spine assessment, the guidelines state that "longitudinal and axial views should be obtained to show normal vertebral alignment and integrity, and an attempt should be made to show

From the early *second trimester* onwards, the commendation is to obtain in standard assessment three standard axial planes (transventricular, transthalamic, and transcerebellar), and,

The measurements for fetal head *biometry* (the biparietal diameter—BPD and the head circumference—HC) are possible when using the transventricular (biventricular) and the transthalamic plane. In the most commonly used technique, the calipers are placed from the outer edge to the

The following chapter is structured as follows:

44 Congenital Anomalies - From the Embryo to the Neonate

variant cerebellar, vermian hypoplasia)

**2.** Ventricular system (ventriculomegaly, aqueduct stenosis)

or abnormal corpus callosum, absent cavum septum)

komalacia, infections, dysplasias, other lesions).

**1.** Normal findings

**2. Normal findings**

intact overlying skin" [9] (**Figure 4**).

if technically feasible, the fetal profile [10] (**Figures 5** and **6**).

(**Figures 1**–**3**).

**Figure 1.** Dating ultrasound scan at 8 weeks of amenorrhea (WA) and 3 days (d). Volumetric ultrasound: sectional planes in the multiplanar mode (a). Subsequently, OmniView facility was used, the line mode (b, c, and d). The embryonic central nervous primitive vesicles can be observed.

inner edge (the "leading edge" technique), at the widest part of the skull, using a perpendicular angle to the midline falx. The HC is measured on the external contour. The cranial bones describe on axial planes a regular *ovoid* shape. The *midline* must be continuous, having no deviations, and the intracranial structures must be symmetrical, mirroring each other's half. Usually, the proximal hemisphere to the probe has a lower visibility, and only the distal one is described by the operator. On the *transthalamic plane*, the anatomic landmarks are (from anterior to posterior) the frontal horns of the lateral ventricles (LVs), the cavum septi pellucidi (CSP), located between

**Figure 2.** The same case, at 10 WA 1d. The same technique was used, after acquiring a static 3D volume.

**Figure 3.** The same case, at 10 WA 1d. The region of interest is placed inside the head, and HD (high-definition) inversion mode surface rendering is applied. This imaging technique acts like a matrix, or a "mold," bringing forth fluid-filled cavities: the early ventricular system.

**Figure 4.** The thalamic plane (a and b), the third ventricle plane (c), and the longitudinal image of the spine, in a prone position (d). In b, the head biometry is represented (measurement of BPD and HC).

the second half of gestation, the depth of the cisterna magna (measured between the cerebellar vermis and the intern margin of the occipital bone) is stable and should not exceed 10 mm.

Fetal Central Nervous System Abnormalities http://dx.doi.org/10.5772/intechopen.76208 47

The *neurosonogram* implies obtaining four more coronal planes and three sagittal/parasagittal planes and assessing the evolving cerebral fissures, gyrations, and circumvolutions [1]. The

The *transfrontal* plane is obtained through the anterior fontanelle. The interhemispheric fissure (IEF) in the median plane and the anterior horns of the lateral ventricles on both sides can be seen. This plane passes anterior to the genu of the corpus callosum (CC), and this is why the IEF appears uninterrupted. The *transcaudate* plane passes at the level of caudate nuclei and the genu of the CC. It interrupts the continuity of the IEF. CSP appears as an anechogenic triangular structure under the CC. Lateral ventricles are seen, surrounded by the cortex. Also, the Sylvian fissures may be identified, laterally. In the *transthalamic* plane, the thalami are seen adjoining. In some cases, the third ventricle is seen in the median plane. In this plane, at the base of the skull, the vessels of the circle of Willis and the optic chiasma

coronal planes are displayed in **Figure 7**.

**Figure 6.** The biventricular (transventricular) and the transcerebellar plane.

**Figure 5.** The thalamic plane.

them as a fluid-filled structure, the two thalami (resembling together a "heart image"), the third ventricle between them, and the hippocampal gyrus. The *biventricular plane* is found just above the previous one and allows the visualization of the lateral ventricles, with the choroid plexus inside them. The width of the posterior horn of the lateral ventricle must be measured using the exact mark of the parieto-occipital sulcus, inside the echoes generated by the ventricular walls, by a direction aligned perpendicularly to the long axis of the ventricle. Before 25 WA, the measurement must be smaller than 8 mm. The *transcerebellar plane* is obtained just below the transthalamic one, in an oblique fashion. The slight posterior tilting allows the visualization of the frontal horns of the lateral ventricles, CSP, thalami, cerebellum, and cisterna magna [1, 10]. The transversal diameter of the cerebellum (in mm) equals roughly the gestational age (in weeks). In

**Figure 5.** The thalamic plane.

them as a fluid-filled structure, the two thalami (resembling together a "heart image"), the third ventricle between them, and the hippocampal gyrus. The *biventricular plane* is found just above the previous one and allows the visualization of the lateral ventricles, with the choroid plexus inside them. The width of the posterior horn of the lateral ventricle must be measured using the exact mark of the parieto-occipital sulcus, inside the echoes generated by the ventricular walls, by a direction aligned perpendicularly to the long axis of the ventricle. Before 25 WA, the measurement must be smaller than 8 mm. The *transcerebellar plane* is obtained just below the transthalamic one, in an oblique fashion. The slight posterior tilting allows the visualization of the frontal horns of the lateral ventricles, CSP, thalami, cerebellum, and cisterna magna [1, 10]. The transversal diameter of the cerebellum (in mm) equals roughly the gestational age (in weeks). In

**Figure 4.** The thalamic plane (a and b), the third ventricle plane (c), and the longitudinal image of the spine, in a prone

position (d). In b, the head biometry is represented (measurement of BPD and HC).

**Figure 3.** The same case, at 10 WA 1d. The region of interest is placed inside the head, and HD (high-definition) inversion mode surface rendering is applied. This imaging technique acts like a matrix, or a "mold," bringing forth fluid-filled

**Figure 2.** The same case, at 10 WA 1d. The same technique was used, after acquiring a static 3D volume.

cavities: the early ventricular system.

46 Congenital Anomalies - From the Embryo to the Neonate

**Figure 6.** The biventricular (transventricular) and the transcerebellar plane.

the second half of gestation, the depth of the cisterna magna (measured between the cerebellar vermis and the intern margin of the occipital bone) is stable and should not exceed 10 mm.

The *neurosonogram* implies obtaining four more coronal planes and three sagittal/parasagittal planes and assessing the evolving cerebral fissures, gyrations, and circumvolutions [1]. The coronal planes are displayed in **Figure 7**.

The *transfrontal* plane is obtained through the anterior fontanelle. The interhemispheric fissure (IEF) in the median plane and the anterior horns of the lateral ventricles on both sides can be seen. This plane passes anterior to the genu of the corpus callosum (CC), and this is why the IEF appears uninterrupted. The *transcaudate* plane passes at the level of caudate nuclei and the genu of the CC. It interrupts the continuity of the IEF. CSP appears as an anechogenic triangular structure under the CC. Lateral ventricles are seen, surrounded by the cortex. Also, the Sylvian fissures may be identified, laterally. In the *transthalamic* plane, the thalami are seen adjoining. In some cases, the third ventricle is seen in the median plane. In this plane, at the base of the skull, the vessels of the circle of Willis and the optic chiasma

**2.1. The spine**

(**Figure 10**).

(**Figure 11**).

specific diagnosis.

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

**Figure 9.** The sagittal plane with HD flow applied, displaying the pericallosal artery (a), the measurement of the nasal

Fetal Central Nervous System Abnormalities http://dx.doi.org/10.5772/intechopen.76208 49

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

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

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

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

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

fetus. Efforts must be made to demonstrate the integrity of the overlying skin.

bone and the fronto-maxillary facial angle, and the parasagittal or oblique plane-1 (c).

quadrangular in shape, and sacral vertebrae are flat.

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

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 vermis.

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

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 cortex.

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

**Figure 9.** The sagittal plane with HD flow applied, displaying the pericallosal artery (a), the measurement of the nasal bone and the fronto-maxillary facial angle, and the parasagittal or oblique plane-1 (c).
