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130
Chapter 3 Biometry of the Fetal Brain
Table 3–20. NOMOGRAM OF THE ATRIAL
WIDTH–HEMISPHERIC WIDTH
RATIO VERSUS GESTATIONAL AGE
Gestational Age (weeks) Mean ± 2 SD (%)
15 49 ± 10
16 47 ± 9
17 46 ± 6
18 42 ± 8
19 35 ± 8
20 20 ± 8
21 33 ± 6
22 27 ± 6
23 23 ± 8
24 22 ± 8
25 20 ± 4
26 21 ± 4
27 19 ± 6
28 18 ± 6
29 16 ± 2
30 14 ± 2
31 17 ± 4
32 15 ± 6
33 17 ± 4
34 15 ± 4
35 17 ± 6
36 13 ± 4
37 13 ± 4
38 13 ± 4
39 14 ± 2
40 14 ± 2
From Pilu and colleagues, 1989,
49
with permission.
POSTERIOR (OCCIPITAL)
HORN OF THE LATERAL VENTRICLES
Definition
The posterior or occipital horn of the lateral ventricles
represents the posterior continuation of the atria of the
lateral ventricles.
How to Measure It ( Figure 3–7 )
The posterior horns (PHs) are better imaged in a horizontal plane at a level slightly above that normally used
for the BPD. They appear sonographically as a sonolucent
area in continuation with the atria, located at the posterior
lobe of the fetal head. To measure them, the electronic
calipers are placed in the echo-dense medial and lateral
walls (PHW). The cerebroposterior horn distance (CPHD)
is measured between the falx cerebri and the lateral wall of
the posterior horn.
50
Comments
As reported by Goldstein’s group,
posterior horn of the lateral ventricles ranges between
5 and 9 mm, with a mean value of 7.06 mm and an SD of
± 1.36 mm throughout pregnancy. The CPHD increases
with advancing gestational age, and the posterior horn
width/CPHD ratio decreases as pregnancy progresses
( Tables 3–23 and 3–24 ). These findings are consonant with
those reported by Siedler and Filly,
that throughout pregnancy, the telencephalic structures
grow at a much faster rate than the diencephalon and the
lateral ventricles.
Callen and associates
52
evaluated the cerebral cortical mantle thickness in fetuses with hydrocephaly. The
sonographic images suggested that the posterior horn
appears to dilate first and more severely than the rest
of the ventricular system. Thus, the evaluation of the
posterior horn probably leads to an early diagnosis of this
pathology.
50
the width of the
51
who demonstrated
TRANSVAGINAL SONOGRAPHY
First Trimester
Definition
A detailed definition of the development of the embryonic and fetal human brain is given in Chapter 1 .
Reading that chapter first will aid in understanding the
development of the structures we describe here using
sonography.
and 3–22 ) indicate that the relative size of the atrium
decreases with brain growth, probably due not to an
actual decrease in its size, which is relatively constant,
but to growth of brain tissue throughout fetal life.
49
How to Measure It
( Figures 3–8 , 3–9 , 3–10 , 3–11 , and 3–12 )
In the extensive work of Blaas and collaborators,
vaginal sonographic evaluation during the first trimester
53 , 54
trans-
Chapter 3 Biometry of the Fetal Brain
Table 3–21. NOMOGRAM OF THE ATRIAL WIDTH–CEREBROATRIAL DISTANCE RATIO THROUGHOUT PREGNANCY
Percentile
131
Gestational Age (weeks) Mean ± 2 SD (cm)
15 0.59 ± 0.086 0.50 0.60 0.70
16 0.70 ± 0.060 0.58 0.72 0.75
17 0.67 ± 0.101 0.53 0.66 0.81
18 0.63 ± 0.058 0.57 0.61 0.71
19 0.56 ± 0.071 0.50 0.53 0.69
20 0.54 ± 0.766 0.42 0.53 0.64
21 0.54 ± 0.043 0.50 0.53 0.62
22 0.48 ± 0.048 0.40 0.50 0.54
23 0.44 ± 0.079 0.31 0.43 0.56
24 0.43 ± 0.094 0.27 0.46 0.57
25 0.37 ± 0.388 0.31 0.39 0.41
26 0.39 ± 0.380 0.35 0.41 0.44
27 0.36 ± 0.067 0.28 0.35 0.44
28 0.37 ± 0.095 0.26 0.35 0.50
29 0.31 ± 0.063 0.20 0.32 0.41
30 0.29 ± 0.046 0.21 0.28 0.35
31 0.34 ± 0.059 0.24 0.37 0.40
32 0.30 ± 0.064 0.17 0.32 0.40
33 0.36 ± 0.070 0.27 0.35 0.44
34 0.30 ± 0.600 0.24 0.27 0.39
35 0.36 ± 0.072 0.29 0.33 0.47
36 0.28 ± 0.043 0.23 0.29 0.33
37 0.25 ± 0.043 0.25 0.25 0.25
38 0.29 ± 0.038 0.27 0.28 0.35
39 0.28 ± 0.034 0.25 0.27 0.32
40 0.33 ± 0.330 0.33 0.33 0.33
From Pilu and colleagues, 1989,
49
with permission.
10th 50th 90th
132
Chapter 3 Biometry of the Fetal Brain
Table 3–22. NOMOGRAM OF THE CEREBROATRIAL DISTANCE–HEMISPHERIC WIDTH RATIO
THROUGHOUT PREGNANCY
Percentile
Gestational Age (weeks) Mean ± 2 SD (cm) 10th 50th 90th
15 0.82 ± 0.090 0.71 0.80 1.00
16 0.73 ± 0.069 0.64 0.71 0.86
17 0.70 ± 0.062 0.61 0.70 0.76
18 0.70 ± 0.055 0.60 0.72 0.75
19 0.65 ± 0.014 0.63 0.65 0.67
20 0.63 ± 0.610 0.55 0.62 0.75
21 0.66 ± 0.046 0.60 0.67 0.73
22 0.60 ± 0.044 0.52 0.61 0.65
23 0.58 ± 0.050 0.54 0.56 0.67
24 0.54 ± 0.040 0.46 0.54 0.59
25 0.58 ± 0.033 0.55 0.57 0.62
26 0.57 ± 0.033 0.53 0.57 0.63
27 0.57 ± 0.025 0.53 0.57 0.60
28 0.51 ± 0.054 0.44 0.49 0.57
29 0.55 ± 0.040 0.51 0.54 0.62
30 0.51 ± 0.050 0.46 0.50 0.61
31 0.53 ± 0.050 0.46 0.53 0.60
32 0.54 ± 0.056 0.46 0.52 0.60
33 0.52 ± 0.042 0.45 0.53 0.58
34 0.30 ± 0.060 0.24 0.27 0.39
35 0.52 ± 0.034 0.48 0.53 0.57
36 0.49 ± 0.024 0.46 0.49 0.52
37 0.57 ± 0.024 0.57 0.57 0.57
38 0.53 ± 0.038 0.48 0.53 0.59
39 0.54 ± 0.026 0.52 0.53 0.57
40 0.50 ± 0.026 0.50 0.50 0.50
From Pilu and colleagues, 1989,
49
with permission.
was accomplished using a high-frequency (7.5 MHz) transducer. The prosencephalon (forebrain) and the mesencephalon (midbrain) were defined using median, oblique,
and horizontal planes. In the median plane, the length and
height of the cavities of the mesencephalon (ML-MH) and
the diencephalon (DL-DH) can be obtained. In the horizontal plane, the widths of the mesencephalon (MW) and
diencephalon cavities (DW), the hemispheres (HW), and
the choroid plexus (CPW) of the lateral ventricles are measured. In the oblique plane, the length of the hemisphere
(HL) can be measured as the longest possible distance
from the anterior to the posterior border of the cortex.
The height of the hemisphere (HH) is measured over the
frontal horn, not including the basal nuclei.
Figure 3–7.
CSP
Chapter 3 Biometry of the Fetal Brain
A
CP
AH
AH
A
CPHD
CP
PHW
133
To evaluate the rhombencephalon (hindbrain), the
scanning plane follows the neuroaxis as it bends. During
week 7, the plane is horizontal (the depth [-RD-] and the
height [-RH-] are measured), gradually tilting to a coronal
plane at the end of the embryonic period. In coronal
planes, the width and height of the cerebellum (CW-CH),
the choroid plexuses (CPW-CPH), and the rhombencephalic cavity (RW—RH) are measured.
Comments
Several studies have demonstrated that sonographic
evaluation of the embryonic central nervous system
(CNS) is possible.
been presented by Blaas and coworkers,
increase in the measurements of all evaluated structures
with advancing gestational age, with the exception of
the width of the diencephalon, which decreases slowly
during the first trimester, probably due to diencephalic wall growth ( Figures 3–13 , 3–14 , 3–15 , and 3–16 ;
Tables 3–25 and 3–26 ).
The expanding field of neurosonoembryology not
only has the potential to evaluate growth but also can help
in diagnosing conditions, such as exencephaly, holoprosencephaly, cephalocele, craniorachischisis, and DandyWalker malformation,
53 – 56
A detailed biometric analysis has
53 , 54
at a much earlier stage than was
Table 3–23. NOMOGRAM OF THE CEREBROPOSTERIOR HORN DISTANCE THROUGHOUT PREGNANCY
Percentile
Gestational Age (weeks) Mean ± 2 SD (mm)
15–16 9.2 ± 0.83 8.0 9.0 10.0
17–18 11.36 ± 1.41 9.0 11.0 13.0
19–20 11.0 ± 1.52 9.0 11.0 13.8
21–22 12.4 ± 1.55 11.0 12.0 15.2
23–24 14.0 ± 1.22 12.0 14.0 15.0
25–26 14.8 ± 1.39 12.0 15.0 16.0
27–28 16.18 ± 2.13 13.0 16.5 19.0
29–30 18.0 ± 2.37 15.2 17.0 22.0
31–32 22.7 ± 2.08 21.0 22.0 25.0
33–34 19.7 ± 3.28 15.0 19.5 25.0
35–36 22.6 ± 3.71 17.0 23.0 27.0
37–38 20.3 ± 3.14 16.0 20.5 25.0
39–40 20.2 ± 2.77 17.0 20.0 23.0
From Goldstein and colleagues, 1990,
50
with permission.
10th 50th 90th
53 , 54
showing an
134
Chapter 3 Biometry of the Fetal Brain
Table 3–24. NOMOGRAM OF THE POSTERIOR HORN
WIDTH–CEREBROPOSTERIOR HORN
DISTANCE RATIO THROUGHOUT
GESTATION
Gestational Age (weeks) Mean ± SD (mm)
15–16 0.67 ± 0.071
17–18 0.60 ± 0.87
19–20 0.60 ± 0.76
21–22 0.51 ± 0.05
23–24 0.46 ± 0.03
25–26 0.49 ± 0.05
27–28 0.42 ± 0.06
29–30 0.43 ± 0.06
31–32 0.37 ± 0.01
33–34 0.41 ± 0.10
35–36 0.41 ± 0.08
37–38 0.39 ± 0.06
39–40 0.47 ± 0.05
From Goldstein and colleagues, 1990,
50
with permission.
previously done with conventional transabdominal scans,
permitting the appropriate management to be carried out
in a timely fashion.
SECOND AND THIRD TRIMESTERS
Definition
Because the evaluated structures are the same as with
transabdominal sonography, there is no need to redefine
them here (see Chapter 2 ).
How to Measure It ( Figures 3–17 ,
3–18 , and 3–19 )
In fetuses in the vertex presentation, transvaginal evaluation of the brain during the second and third trimesters
can be accomplished by aligning the ultrasound beam
of the transducer with the longitudinal axis of the fetal
head through the anterior fontanelle.
alignment, the fetal head can be gently manipulated by the
free hand of the examiner. If the fetus is in a nonvertex
presentation, and the transabdominal scan is suboptimal,
an external cephalic version may be considered in selected
cases. Usually, end-firing probes with frequencies of
5 or 7.5 MHz are used.
be used to measure the cerebral ventricles in the following
57,58
fashion.
(See description of measurement in oblique
57 , 58
Oblique and coronal planes can
and coronal planes.)
57
To allow proper
Figure 3–8. M, Mesencephalon; 3, diencephalon.
Mes
ML
MH
DH
M
Di
DL
3
Chapter 3 Biometry of the Fetal Brain
135
DESCRIPTION OF MEASUREMENTS IN OBLIQUE AND CORONAL PLANES
57,58
Number Plane Measurement
1 Oblique– 1 ( Figure 3–17 ) Thalamus–choroid plexus interface to the tip of the posterior
(occipital) horn (TCP-TOH)
2 Choroid plexus thickness (CPT)
3 Posterior (occipital) horn height (OHH)
4 Midcoronal–2 ( Figure 3–18 ) Midline to the upper edge of the lateral ventricle (MUELV)
5 Depth of the lateral ventricle (DLV)
6 Occipital–1 (posterior coronal)
Width of the posterior (occipital) horn (WOH)
( Figure 3–19 )
7 Height of the posterior (occipital) horn (HOH)
Ratio Thalamus to tip of posterior horn (TCP-TOH)/choroid plexus
thickness (CPT)
Ratio Posterior horn height (oblique plane) (OHH)/choroid plexus
thickness (CPT)
Comments
In 1989 Kushnir and colleagues
transvaginal sonography to examine certain biometric
parameters (CRL, BPD, HC, LVW, and HW) in a group
of 50 patients whose pregnancies were between 12 and 14
gestational weeks. In 1991 our group
first time the feasibility of the routine transvaginal sonographic evaluation of the fetal brain during the second
half of pregnancy. With this approach, using the anterior
fontanelle, images of diagnostic quality of the intracranial
59
proposed the use of
57
described for the
anatomy can be obtained. The differentiation between
normal and pathologic brain structures is easier and avoids
the disadvantages of the transabdominal route. Such
disadvantages may be (1) the inadequate visualization of
the cerebral hemispheres due to reverberation artifacts, a
deeply engaged fetal head, or maternal obesity and abdominal scarring; and (2) the presence of pseudohydrocephalus, unilateral hydrocephaly, and pseudoepidural artifact,
which are detected using conventional axial planes.
60
Using this technique, nine nomograms of the fetal
lateral ventricles were developed and evaluated using the
Hemisphere
Lateral
choroid
plexus
Diencephalon
Mesencephalon
‘Blindsäcke’
Cerebellum
Figure 3–9. H, Hemisphere; 3, diencephalon; 4, rhombencephalon. (From Blaas HG and colleagues, 1995 with permission.)
DW
MW
HW
CPW
H
3
4
H
136
Chapter 3 Biometry of the Fetal Brain
Figure 3–10.
RH
RD
Rhombencephalon
Mesencephalon
Hem
HH
ChPI
HL
4
Diencephalon
Y
Hemisphere
Figure 3–11. M, Mesencephalon; 4, rhombencephalon. (From Blaas HG and colleagues, 1995 with permission. )
Mesencephalon
Cerebellum
CH
Fourth ventricle
Choroid plexuses
CW
RW
RH
CPH
CPW
CRL 25
M
Mesencephalon
Mesencephalon
Cerebellum
Cerebellum
Choroid plexus
Choroid plexus
Medulla oblongata
Medulla oblongata
MM
Figure 3–12. (From Blaas HG and colleagues, 1995 with permission. )
25
20
Chapter 3 Biometry of the Fetal Brain
20
137
15
10
Length (mm)
5
0
78 9
10
8
6
4
Width (mm)
2
0
78 9
15
10
10 11
10 11
12
12
13
13
15
10
Length (mm)
5
0
8910
8
6
4
Width (mm)
2
0
8910
10
8
6
11
11
12
12
13
13
Height (mm)
5
0
78 9
Gestational age based on
last menstrual period (weeks)
10 11
12
13
Figure 3–13. Hemispheres. (From Blaas and colleagues, 1994 and 1995,
with permission. )
sagittal and coronal planes ( Tables 3–26 through 3–36 ).
The occipital plane is usually the hardest to image due
to maternal discomfort while maneuvering the probe.
Measurements such as the TCP-TOH, OHH, and MUELV
increased in a linear fashion as pregnancy advanced.
Measurements such as the CPT, DLV, WOH, HOH, and
the ratios TCP-TOH/CPT and OHH/CPT demonstrated
little, if any, association with gestational age.
60
One of the major applications of these nomograms
is the early diagnosis of hydrocephaly. Two early changes
have been described. The first is the dilation of the
4
Height (mm)
2
0
8910
Gestational age based on
last menstrual period (weeks)
11
12
13
Figure 3–14. Choroid plexus of the lateral ventricle. (From Blaas and
colleagues, 1994 and 1995, with permission. )
posterior horn in an up-and-down fashion, where the
resistance to the cerebrospinal fluid (CSF) pressure is
61 , 62
least,
the choroid plexus, probably as a result of the increasing
CSF pressure.
and the second is the squeezed appearance of
63
In our experience,
58
measurement of the
choroid plexus alone was not discriminatory, but when its
thickness was used as a denominator in the two ratios, it
became a very sensitive measurement. We propose that
although all seven measurements may add important clinical information, evaluation of the OHH (number 3) in the
oblique–1 plane and measurements of the lateral ventricle
138
Chapter 3 Biometry of the Fetal Brain
5
4
3
2
Length (mm)
1
0
78910
2
1
Width (mm)
0
789
10 11
12
13
8
6
4
Length (mm)
2
0
7
3
2
1
Width (mm)
0
7
3
2
8
8
10 11 12
9
10
9
11
12
13
13
4
3
2
Height (mm)
1
0
78910
Gestational age based on
last menstrual period (weeks)
Figure 3–15. Diencephalon. (From Blaas and colleagues, 1994 and
1995, with permission. )
and the HOH (numbers 5 and 7) in the midcoronal–2 and
occipital–1 planes are the best markers of early ventricular
dilation. If a single plane had to be chosen as the first-line
indicator of ventriculomegaly with the transvaginal route,
the oblique–1 plane should be selected because in this
plane the OHH can be obtained, and the two ratios can be
calculated.
58
1
Height (mm)
0
7
8 9 10 11 12 13
Gestational age based on
last menstrual period (weeks)
Figure 3–16.
1995, with permission. )
Mesencephalon. (From Blaas and colleagues, 1994 and
Transvaginal neurosonography not only has a place
in the diagnosis of ventricular dilation, but also can be of
invaluable help in diagnosing almost any type of congenital
CNS anomaly.
64
The sonographic planes described can also
be used for evaluating the appearance and development
of the corpus callosum. By 18 weeks of gestation, all the
components of the corpus callosum are present and can
be visualized on transvaginal sonography in ~95% of
cases ( Table 3–27 ).
65
Transvaginal sonography provides an
excellent method for direct examination of this structure,
allowing for the diagnosis of anomalies such as agenesis
and hypogenesis, as well as more subtle findings associated
with “callosal thinning,” particularly in cases of infection,
periventricular leukomalacia, inborn errors of the metabolism, and anomalies of neuronal migration.
Chapter 3 Biometry of the Fetal Brain
Table 3–25. EQUATIONS OF THE REGRESSIONS, INCLUDING THE 95% PREDICTION INTERVALS
Independent Variable Dependent Variable Equations
Hemispheres
Gestational age Length y = (−3.34 + 0.62x ± 1.96 × 0.26)
Gestational age Width y = (−1.45 + 0.33x ± 1.96 × 0.21)
Gestational age Depth y = (−1.25 + 0.34x ± 1.96 × 0.22)
Choroid plexus of the lateral ventricles
Gestational age Length y = (−3.99 + 0.63x ± 1.96 × 0.29)
Gestational age Width y = (−1.71 + 0.32x ± 1.96 × 0.21)
Gestational age Height y = (−1.55 + 0.32x ± 1.96 × 0.19)
Diencephalon
Gestational age Length y = –2.15 + 0.575x ± 1.96 × 0.63
Gestational age Width y = 1.63 – 0.07x ± 1.96 × 0.24
Gestational age Height y = −0.87 + 0.28x ± 1.96 × 0.34
Mesencephalon
Gestational age Length y = −0.32 + 0.42x ± 1.96 × 0.54
Gestational age Width y = 0.54 + 0.1x ± 1.96 × 0.28
Gestational age Height y = 0.01 + 0.16x ± 1.96 × 0.28
2
2
2
2
2
2
139
The gestational age is based on the date of the last menstrual period.
From Blaas and colleagues, 1995,
54
with permission.
Table 3–26. MEAN SIZE AND 95% PREDICTION INTERVALS OF THE RHOMBENCEPHALIC STRUCTURES
Rhombencephalon (mm) Cerebellum (mm) Chorold Plexus (mm)
Gestational Age
(weeks + days)
7 + 0 3.8 (2.2–5.3) 2.1 (0.6–3.7) 1.5 (0.4–2.6)
8 + 0 3.9 (2.3–5.4) 3.1 (1.5–4.7) 2.1 (1.0–3.2)
9 + 0 4.0 (2.5–5.6) 3.8 (2.2–5.4) 2.5 (1.5–3.6) 4.8 (3.0–7.1) 1.4 (0.7–2.1) 3.2 (1.8–4.6) 1.1 (0.6–1.6)
10 + 0 4.1 (2.6–5.7) 4.3 (2.7–5.8) 2.9 (1.8–3.9) 5.8 (3.8–8.3) 1.7 (1.0–2.4) 3.5 (2.1–4.9) 1.1 (0.6–1.6)
11 + 0 4.3 (2.7–5.8) 4.5 (2.9–6.1) 3.1 (2.0–4.2) 6.9 (4.7–9.6) 2.1 (1.4–2.8) 3.8 (2.4–5.2) 1.2 (0.7–1.7)
12 + 0 4.4 (2.8–5.9) 4.5 (2.9–6.1) 3.2 (2.2–4.3) 8.1 (5.7–11.0) 2.5 (1.8–3.2) 4.1 (2.7–5.6) 1.3 (0.8–1.8)
From Blaas and colleagues, 1995,
Length Width Depth Width Height Width Height
54
with permission.