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40
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
Median
Coronal Coronal
Median
Ant
Ant
Ant
Ant
Horizontal
A
Coronal
Horizontal
B
Median
Ant
Horizontal
C
Ant
Ant
Figure 2–28. Structural evaluation of the fetal brain at 15 postmenstrual weeks. Systematic scanning of the lateral ventricles and the choroid plexus can
be performed using several horizontal or oblique planes. (A) Frontal view of the inversion rendered ventricles. (B) Lateral view of the inversion rendered
ventricles. (C) Superior view of the inversion rendered ventricles. (From Timor-Tritsch and colleagues, 1995,
42
with permission.)
7w 6d 9w 2d
8w 1d
10w 4d 11w 1d 12w 0d
Lateral
view
Frontal
view
Superior
view
Figure 2–29.
lateral, frontal, and the superior views. Note the changing relations of size between the anterior horns and the rhombencephilon (fourth ventricle).
(From Timor-Tritsch IE et al, 2008,39 by permission.)
Composite picture of the 3D inversion renderings of the developing ventricular system from 7 to 12 postmenstrual weeks showing the
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
(sagittal)
41
Coronal
Mesencephalon
Aqueduct (Sylvius)
Diencephalon–
future third ventricle
Median
Median
(sagittal)
Isthmus
Axial
Rhombencephalon
– future fourth ventricle
Myelencephalon
future third
Lateral view Anterior view
Coronal
Ant
Horizontal
Mesencephalon
Diencephalon
ventricle
Ant
Rhombencephalon
future fourth ventricle
Interhemispheric
foramina (Monro)
Median
Telencephalon– future lateral ventricles and hemispheres
future lateral ventricles and hemispheres
Telencephalon–
Figure 2–30. Inversion rendering of brain ventricles at 8 postmenstrual weeks and 1 day. The upper left and right pictures are orthogonal displays
and the resulting 3D inversion renderings offering a lateral (upper left) and an anterior (upper right) view of the cast-like appearance of the ventricles. The two lower pictures detail the anatomic structures seen on the lateral and the anterior views of the 3D inversion renderings. (From TimorTritsch IE et al, 2008,
39
by permission.)
42
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
Median
(sagittal)
Ant
Ant
A
l
Orthogonal
Horizonta
Corona
display
B
DC
Figure 2–31. Inversion rendering of brain ventricles at 9 postmenstrual weeks and 2 days. (A) Orthogonal display. (B) Tomographic display: sag-
ittal sections with lateral view of 3D inversion rendering. (C) Tomographic display: coronal sections with frontal view of 3D inversion rendering.
(D) Tomograpich display: horizontal sections with superior view of 3D inversion rendering. (From Timor-Tritsch IE et al, 2008,
interventricular foramina (Monro) into the space
between the thalami (virtual space of the third ventricle), the cavum septi pellucidi below the corpus
callosum, the longitudinal fissure, the budding (at 28
postmenstrual weeks) or the developed (after 31 to
32 postmenstrual weeks) cingulate gyrus and sulcus,
as well as the triangular subarachnoid space containing the superior sinus ( Figures 2–38A – C , 2–39A–E ,
2–40B and 2–41A – D ).
Structures seen in the midcoronal–3 plane are
the lateral ventricles (body) containing the choroid
plexuses; at times, the slightly echogenic choroid
plexus of the third ventricle between the thalami; the corpus callosum; the longitudinal fissure;
and the cingulate gyrus and sulcus. Also, toward
term, the secondary and tertiary branches of the
cingulate sulcus can be imaged ( Figures 2–38A and
C , and 2–39D ).
3. OCCIPITAL SECTIONS: The occipital oblique sections may be the hardest to obtain.
20,23 , 32 , 41 , 42
If circumstances permit, two distinct sections can be
obtained. The occipital–1 section displays the typical
owl’s eye configuration because the cortical and
white matter is seen in a symmetrical fashion surrounding the sonolucent and almost perfectly round
posterior horns, above the V-shaped subarachnoid
space and below the tentorium and the hemispheres
of the cerebellum. At times, the fourth ventricle and
the hyperechoic vermis are seen ( Figures 2–38C ,
2–39E , and 2–41D ).
The occipital–2 section is the most posterior one.
Rarely seen, however, it contains the tip (smallest
sonolucent circle) of the posterior horn and the
tentorium, below which the cerebellar hemispheres,
vermis, and cerebellomedullary cistern (the cisterna
magna) are seen ( Figure 2–30 ).
A faster way to scan the fetal brain in the coronal
plane is to use one each of the frontal, midcoronal, and
occipital sections. On the frontal–1 section, besides
its symmetrical picture, one should not see the anterior horns (these are seen on this section in the case
of ventriculomegaly). The midcoronal–2 section
should contain the corpus callosum and the left and
right thalami, and the choroid plexus should fill the
39
by permission.)
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
43
Median
Ant
Horizontal
A
Figure 2–32. Inversion rendering of brain ventricles at 10 postmenstrual weeks and 4 days. (A) Orthogonal planes and lateral view of 3D inversion
rendering. (B) Orthogonal planes and anterior view of 3D inversion rendering. (C) Orthogonal planes and superior view of 3D inversion rendering.
(From Timor-Tritsch IE et al, 2008,39 by permission.)
Coronal
Ant
Median
Ant Ant
C
Horizontal
Median
Horizontal
B
Coronal
Ant
Coronal
body of the lateral ventricle, proceeding through the
interventricular foramina. The occipital–1 section
should show the normal-size posterior horn (see its
normal measurements in Chapter 3 ), and the tentorium and the cerebellum should fill the posterior
fossa. This abbreviated scanning algorithm should
not take more than several minutes.
Structures Seen on Sagittal Sections
Unlike the coronal section, in which the right and left
hemispheres are scrutinized simultaneously, sagittal sections are different, since after the image in the median
plane is obtained, the right and left hemispheres have to
be scanned separately using right and left paramedian or
oblique sections.
Table 2–3 contains the pertinent images seen with
each of the following structures.
1. MEDIAN SECTION: The hallmark of the median
section are the corpus callosum and, below it, the
sonolucent cavum septi pellucidi. In addition, the
thalamus, the head of the caudate nucleus, their
thin-covering tela choroidea, parts of the midbrain,
and posteriorly, the hyperechoic vermis are depicted
( Figures 2–42 , 2–43A , 2–44 , and 2–45 ). Recognition
of these structures on this section at 14 postmenstrual
weeks is dependent on the quality and resolution of
the transducer ( Figure 2–34 ).
The appearance of the corpus callosum is age
dependent and is discussed below. As an example, at
16 postmenstrual weeks ( Figure 2–38B ), the corpus
callosum is not yet evident.
At times, as a function of the transducer (age
dependent) or the depth at which it is situated, the
fourth ventricle and the cerebellomedullary cistern
become visible ( Figures 2–43A and 2–45 ).
2. OBLIQUE–1 (RIGHT AND LEFT) SECTIONS: The
oblique–1 sections should be obtained on the right
as well as the left side. Although the sizes of the
ventricles in both hemispheres should be the same,
slight discrepancies are common. These sagittal
sections are of importance and should never be
overlooked. Lately, using 3D fetal neuroscanning
techniques, we have named such oblique planes the
three-horn views because they enable the viewer to
evaluate the anterior, posterior, and inferior horns on
the same section (see Chapter 9 ).
44
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
Coronal Coronal
Median
Median
Ant
Horizontal Horizontal
Ant
AB
Ant
Coronal
Ant
Median
Horizontal
Ant
C
Ant
Lateral view
Posterior
horn
Lateral
ventricle
Rhombencephalon
Anterior
horn
Imprint of the
Lateral
ventricle
Anterior
Posterior
horn
choroid plexuses
Superior view
Rhombencephalon
Lateral
ventricle
Myelencephalon
Anterior view
Posterior
horn
horn
Anterior
horn
D
Myelencephalon
Figure 2–33. Inversion rendering of brain ventricles at 11 postmenstrual weeks and 1 day. (A) Orthogonal planes and lateral view of 3D inversion
rendering. (B) Orthogonal planes and anterior view of 3D inversion rendering. (C) Orthogonal planes and superior view of 3D inversion rendering.
(D) Anatomic structures seen on the lateral superior and anterior views of the 3D inversion renderings. Observe the “imprint” of the choroid plexus.
(From Timor-Tritsch IE et al, 2008,
39
by permission.)
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
AB
45
CD
Figure 2–34.
plane with an inversion rendering of the relatively large (but normal) anterior horns of the lateral ventricles viewed from the front. (D) Orthogonal plane
with an inversion rendering of the relatively large (but normal) anterior horns of the lateral ventricles viewed from above.
Fetal brain scan at 12 postmenstrual weeks. (A) Sagittal serial tomographic images. (B) Axial serial tomographic images. (C) Orthogonal
At 14 postmenstrual weeks the anterior horn
is relatively large, and the posterior horn is barely
developed and difficult to image ( Figures 2–34 ,
2–35A , B, and 2–38B). At times, the inferior horn
is visible in normal fetuses at this age ( Figure 2–42 ).
Later, these sections should not contain the inferior
horn of the lateral ventricle ( Figure 2–31D ) because
this horn is barely open in a normal brain.
At or after 18 postmenstrual weeks, the anterior
horn progressively decreases in size. Toward term
it may not be visible at all. The choroid plexus fills
the entire antrum above the thalamus. The posterior
horn increases its relative size and is easily imaged
( Figures 2–40A and 2–43B ).
3. OBLIQUE–2 (RIGHT AND LEFT) SECTIONS: If,
after scanning through the sagittal planes, the
scanning plane of the transducer is further tilted
toward the fetal ears, almost tangential scans of
the cerebral hemispheric surfaces are obtained.
Typical on this section is the still widely gaping
lateral sulcus (Sylvius), which appears as if the
capital letter V were lying on its side. The apex of
the V points toward the occiput ( Figure 2–43C ).
The more advanced the age, the more closed the
lateral fissure becomes. Between the two “legs”
of the letter V, the tangentially “touched” insula is
imaged. The upper lip of the V-shaped edges of the
fissure is called the parietal operculum; the lower
lip is the temporal operculum.
D
Horizontal (Axial) Planes
At times in the early second trimester the fetus turns conveniently into a position in which an axial view is most
revealing. The bone of the skull is still thin enough to
enable meaningful TVS scrutiny of the brain.
The horizontal planes allow the gathering of information on two important aspects of brain anatomy. The
first is the examination of the entire choroid plexus of the
lateral ventricles ( Figure 2–34 ) using different ascending
sections. The second is a careful look at the posterior fossa
using a posteriorly tilted axial plane ( Figures 2–53 , 2–59 ,
and 2–60 ). The images of the posterior fossa are discussed
subsequently.
Having pioneered the fetal transfontanelle neuroscan
using the high-frequency transvaginal US probe, we are
aware of the following.
1. The sections and/or planes obtained through the
anterior fontanelle using conventional 2D transvaginal neurosonography were adopted emulating
the neonatal transfontanelle approach. All sections
are obtained by placing the footprint of the vaginal probe on the anterior fontanelle; the sections
therefore “radiate” from one point: the fontanelle.
Almost every plane, except the median and one
coronal plane, is angled or is oblique and are therefore not parallel to each other. Moving the probe
in a fanlike manner from anterior to posterior to
obtain the coronal sections and from side to side
46
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
2B
2A
1B
1A
CP
1
C
CM
1A 1B
Figure 2–35. Median, paramedian, and left oblique sections at 14 postmenstrual weeks. 1A . Median section showing the thalamus (T), the hypoechoic
cerebellum (C), and the posterior cisterna magna (CM). 1B. Slightly more lateral paramedian sagittal section showing the relationship between the anterior horn (AH) and the choroid plexus (C) and the thalamus (T). 2A, 2B. Left oblique views also depicting the posterior horn (OH). (From Timor-Tritsch
and Monteagudo, 1991,
24
with permission.)
to obtain the sagittal sections results in the desired
planes.
2. In contrast to the 2D technique, when a volume of
the fetal brain is obtained using the 3D transvaginal
US probes through the anterior fontanelle, the volume of the fetal brain can be sequentially sectioned
at demand in all three classical orthogonal planes.
These planes are parallel to each other and are therefore comparable to those sections obtained using
serial tomograms by CT or MRI.
3. Using 3D volume scans, it is easy to render scanning
AH
T
neurosonography. Guidelines to perform a basic sonographic examination of the fetal CNS were published in
Ultrasound in Obstetrics and Gynecology .
nation employs only transabdominal US, and its objective is to evaluate the fetal brain only in the general axial
(horizontal) planes. It includes three planes: transventricular, transthalamic, and trancerebellar planes, as seen
in Figure 2–46 . In contrast, the targeted or more detailed
fetal neurosonogram contains other planes and sections,
such as coronal planes ( Figure 2–47 ) and sagittal planes
( Figure 2–48 ).
2
2A
2B
43
This exami-
planes that are almost impossible to obtain as a routine procedure. An example is the rendering of axial
sections.
Although we use the 2D fetal transfontanelle neuro-
scan initiated by us,
20,23,24,41
we are increasingly aware of
the new, more advanced 3D technique to examine the fetal
brain, which will be demonstrated later in this chapter.
Ventricular System
The embryology of the cerebral ventricles was touched
on in Chapter 1, as well as in this chapter. The fetal
cerebral ventricular system, as far as ultrasonography
is concerned, consists of the following interconnecting
structures and their parts ( Figure 2–49 ): the lateral ventricles—anterior (frontal) horn, body, atrium, posterior
Basic and Targeted Fetal Neurosonogram
The International Society of Ultrasound in Obstetrics
and Gynecology (ISUOG) attempted to standardize fetal
(occipital) horn, and inferior (temporal) horn—and the
interventricular foramina (Monro)—third ventricle, cerebral aqueduct (Sylvius), fourth ventricle, median aperture
(Magendie), and lateral apertures (of Luschka).
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
CP
47
AH
AH
T
AH
FRONTAL
FRONTAL
13 W 3 D
13 W 3 D
A
Figure 2–36.
image is to show the relatively large and sonolucent anterior horns (AH). (A) Frontal slightly slanted section taken at the plane shown by the white line
in (B) Left oblique section showing the thalamus (T), on top of which the hyperechoic choroid plexus (CP) is seen. Note the ample free space, which is
normal at this age.
This image depicts the anterior part of the fetal brain at 13 weeks and 3 days from the last menstrual period. The importance of this
B
LP
RP
A
LF
RF
B
16w
Figure 2–37. Images of the fetal skull bones, the fontanelles, and sutures at approximately 16 and at 20 [KT1]postmenstrual weeks. (A) Tangential
view of the main fontanelle (arrow) through which transvaginal scanning of the fetal brain is performed (ie, the anterior fontanelle). The left and right
frontal and parietal bones are also seen (LF, RF, LP, and RP, respectively). (B) An anterior coronal (almost tangential) section of the fetal skull showing
the anterior fontanelle (arrow).
48
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
Table 2–2. THE CORONAL PLANES
Anatomical
Structures
Skull Orbit
Lateral
Intraventricular
Ventricles &
Connections
Cavum septi pellucidi Cavum septi pellucidi
Midbrain
Cerebellum
foramen
Third (Virtual
Corp. callosum Genu Trunk Splenium
Head of
caudate
nucleus
Thalamus Thalamus
Hemisphere Hemispheres
Vermis Vermis
4th Ventricle 4th
FRONTAL GROUP MID-CORONAL GROUP OCCIPITAL GROUP
1212 3 12
Only at
<16w
Ant. horn Body
Caudate
nucleus
Body Atrium
Post. horn
Choroid plexus
With
choroid
plexus
space)
Tela
choroidea
Ventricle
(at times)
Meninges
Falx F A L X
Tentorium Tentorium
Cisterna magna Cisterna
This table summarizes the brain structures imaged on each of the consecutive frontal, midcoronal, and occipital sections.
Reproduced Timor-Tritsch et al, 1996,41 with permission.
magna
Chapter 2 Normal Two- and Three-Dimensional Neurosonography of the Prenatal Brain
49
F-1
F-2
MC-1
A
MC-2
MC-3
O-2
O-1
Ob-1
B
M
Figure 2–38. ( A) Serial “coronal” sections at 16 postmenstrual weeks from frontal to occipital. Note the anterior fontanelle on F–1, the wide-open
anterior horns on F–2 and on MC–1. The incipient cavum septi pellucidi (arrows) are seen on MC–2 and on MC–3. F, Frontal; MC, midcoronal; O,
occipital. (B) The Median (M) and Oblique–1 (OB–1) sagittal sections of the same fetus at 16 postmenstrual weeks. Note that the corpus callosum is
not yet developed and that the lateral ventricles are relatively large on the OB–1 section.