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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5759_Библиотеки_им_академика_М_И_Перельмана
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Chapter 28 ■ Overview of Obstetric Imaging 1047
A
C
FIGURE 28-8. Determination of situs. A, Scan plane, and B, transverse scan diagram. With fetus in cephalic position and spine
on the maternal right side, the left-sided stomach is “up” on the side closest to the transducer. C, Scan plane, and D, with the fetus in
breech position and spine on the maternal right side, the left-sided stomach is “down” on the side farthest away from the transducer.
B
D
ADDITIONAL VIEWS FOR TARGETED
FETAL SONOGRAMS*
Corpus callosum
Cerebellar vermis
Outflow tracts
Orbits
Extremities, including hands and feet
Profile/chin
Nuchal fold (at appropriate gestational age)
Individual long-bone measurements
Hands and feet
*These are not established imaging guidelines but rather
the author’s suggestions regarding views that are helpful
in most targeted scans. Additional views may be needed
depending on the indications for the obstetric/fetal
examination.
(Fig. 28-12; Video 28-3), abdomen and pelvis (Fig.
28-13; Videos 28-4 and 28-5), spine (Fig. 28-14),
extremities (Fig. 28-15), and umbilical cord (Fig.
28-16). Other specialized sonographic examinations
include fetal Doppler sonography, biophysical profile,
fetal echocardiography, and additional biometric
measurements.
ROUTINE ULTRASOUND
SCREENING
Estimation of Gestational Age
Determination of the expected date of delivery (EDD)
is especially important in obstetric practice because it is
Text continued on p. 1055.
1048 PART IV ■ Obstetric Sonography
A
B
C D
FIGURE 28-9. Second-trimester biometry. A, Biparietal diameter. Note the level of this ultrasound image at the thalamus
and third ventricle. The calipers are placed from the outer skull in the near field to the inner skull in the far field. B, Head circumference.
Note how circumference is measured around the outside of the skull. Arrow depicts cavum of the septum pellucidum. C, Abdominal
circumference. Note the curve of the portal vein and stomach on this transverse image, with circumference drawn around the outside of
the skin. D, Femur length. Note that the “upside” femur should be measured, with the shaft of the bone as near to perpendicular to the
scan plane as possible, excluding the distal femoral epiphysis.
Chapter 28 ■ Overview of Obstetric Imaging 1049
A
B
C D
FIGURE 28-10. Routine sonographic views of fetal head. In addition to the biparietal diameter and head circumference,
required views of the head include images of the cerebral ventricles, cerebellum, cavum of the septum pellucidum, and midline falx.
Additional views that can be obtained are angled views to demonstrate both sides of the choroid plexus, and views through the anterior
fontanelle or midline sutures to demonstrate the corpus callosum. A, Axial image shows cerebral ventricles filled with choroid plexus.
B, Angled axial view shows both ventricles with choroid plexus. C, Axial image shows cerebellum (arrow) and cavum of the septum pel-
lucidum (arrowhead). D, Transvaginal sagittal view of the corpus callosum (arrows).
1050 PART IV ■ Obstetric Sonography
A
B
C D
FIGURE 28-11. Views of fetal face. Required view of the face is of the nose and lips. Additional views include orbits and profile.
A, Coronal view of nose and lips. B, Coronal view of orbits. C, Sagittal view of facial profile. D, 3-D image of fetal face.
Chapter 28 ■ Overview of Obstetric Imaging 1051
A
C
B
D
E
FIGURE 28-12. Views of fetal heart and outflow tracts. Required views include demonstration of normal situs, with heart
and stomach on left side, four-chamber view of the heart, documentation of normal heart rate, and outflow tracts “if possible”. A, Axial
image shows normal four-chamber view of fetal heart. Note the normal axis of the heart, at about 60 degrees from midline. B, M-mode
ultrasound. Note normal heart rate (146 beats/min). C, Angled view shows left ventricular outflow tract (arrow) with heart and stomach(s)
on the same side of the fetus. D and E, Right ventricular outflow tract in oblique axial (D) and oblique sagittal (E) views with ductus
arteriosus (arrow) extending posteriorly to aorta.
1052 PART IV ■ Obstetric Sonography
A
B C
D E F
G
FIGURE 28-13. Views of fetal abdomen and pelvis. Note normal stomach documented on abdominal circumference view
(Fig. 28-9, C ). Other required views are cord insertion, kidneys, and bladder. Additional views document the diaphragm and fetal gender.
A, Cord insertion site in the anterior abdominal wall. B and C, Transverse views of kidneys at 18 and 28 weeks’ gestation. A small amount
of central renal pelvic dilation (2 mm in this fetus) is a normal finding. D, Transverse image of bladder. Note umbilical arteries on either
side of bladder. E, Sagittal view shows liver, diaphragm (arrow), and lungs. Note how the liver is of lower echogenicity than the lungs.
F, Male genitalia. G, Female genitalia.
Chapter 28 ■ Overview of Obstetric Imaging 1053
A
C
D
B
E
FIGURE 28-14. Views of fetal spine. Note transverse image of thoracic spine on four-chamber view (Fig. 28-12, A) and transverse
image of lumbar spine between the kidneys (Fig. 28-13, B and C ) and umbilical cord insertion site (Fig. 28-13, A). A, Transverse image
of cervical spine. B, Transverse view of lumbosacral spine. Note how the posterior elements point towards each other and the skin covers
the distal spine. C, Oblique sagittal image of cervical and thoracic spine. D, Oblique sagittal view of entire spine. E, Sagittal view focused
on the distal spine. Note how the spinal canal narrows and has a gentle upturn distally. (See also Video 28-4.)
1054 PART IV ■ Obstetric Sonography
A
B C
D E F
G H
FIGURE 28-15. View of fetal extremities. Required views include documentation of all four extremities. Additional views
include measurements of all the long bones and demonstration of the fingers and toes. A and B, Lower extremities. C, D, and E, Upper
extremities. F, Hand. Note four fingers with thumb partially out of the field of view. G, Foot. H, 3-D view of upper extremity. (See also
Fig. 28-11, D, for 3-D view of hands.)
Chapter 28 ■ Overview of Obstetric Imaging 1055
A
C
FIGURE 28-16. Views of umbilical cord. Required views include cord insertion site into the anterior abdominal wall (see Fig.
28-13, A) and documentation of number of vessels in the umbilical cord. Additional views include cord insertion site into the placenta
and Doppler examination of the cord. A, Transverse image of three-vessel umbilical cord. Note two arteries (arrows) that are smaller
than the single vein (arrowhead). (See also Video 28-5 and Fig. 28-13, D.) B, Color Doppler longitudinal image of three-vessel cord. C,
Cord insertion site (arrow) into the placenta. D, Spectral Doppler image documents normal umbilical arterial systolic/diastolic ratio in
third-trimester fetus.
B
D
used to intervene in pregnancies considered to be “growth
restricted” and in postterm pregnancies. Multiple studies
have demonstrated that routine use of ultrasound results
in more accurate assessment of the EDD than last menstrual period (LMP) dating or physical examination,
even in women with regular and certain menstrual
10-13
dates.
Pregnancy dating is most accurately performed in the first half of pregnancy. Fetal growth
should be assessed by comparison to earlier scans in
pregnancy. In a Cochrane review of nine trials of routine
ultrasound in early pregnancy, routine use of early ultrasound and the subsequent adjustment of the EDD led
to a significant reduction of postterm pregnancy.
14
A rule of thumb is that in the first trimester, LMP
dating should be maintained unless ultrasound yields an
EDD more than 7 days off; in the second trimester,
ultrasound should be used to change EDD if it is off by
more than 2 weeks (and follow-up is then needed to
1056 PART IV ■ Obstetric Sonography
ensure appropriate interval growth); and in the third
trimester, a 3-week discrepancy between LMP and ultrasound dating is allowed, but needs to be taken into the
clinical context, with assessment for growth restriction
or macrosomia, if appropiate. It is important to recognize that if a pregnancy is redated after the first trimester,
follow-up is needed to assess for appropriate interval
growth (see Chapter 42).
Identification of Twin/Multiple
Pregnancies
A major benefit of routine ultrasound screening is early
identification of multiple gestations.
4,11,15-17
Randomized
clinical trials comparing routine second-trimester ultrasound examination with sonography performed for clinical indications have shown that a substantial number of
twin pregnancies are not recognized until the third trimester or delivery in women who do not undergo routine
ultrasound. The improved diagnosis of twins leads to
improved perinatal outcome because of a reduced incidence of low birth weight, smallness for gestational age,
prematurity, depressed Apgar scores, and stillbirths.
15
Screening and Perinatal Outcomes
The value of a routine second-trimester scan in apparently normal pregnancies to identify those at high risk
for unsuspected problems is controversial. Many countries perform one, two, or even three sonograms as part
of routine obstetric care.
16,18,19
standing of fetal anomalies when pregnancies with fetal
anomalies are continued, are difficult to demonstrate.
The Helsinki trial reported a significant decrease in
perinatal mortality among the ultrasound-screened
group, from 9 to 4.6 per 1000.
16
This was attributed to
the relatively high rate of detection of fetal anomalies in
that study (58% of major malformations were detected
before 24 weeks) with subsequent termination of fetuses
with anomalies.
In the Routine Antenatal Diagnostic Imaging with
Ultrasound (RADIUS) trial, the investigators did
not find a significant difference in “adverse perinatal
outcome,” defined as fetal death, neonatal death, or neonatal morbidity, in the screened versus control groups.
The explanation for the lack of improved outcome was
the limited sensitivity of routine sonography in the
detection of congenital abnormalities (16.6% before 24
weeks and 34.8% before 40 weeks) coupled with a low
rate of pregnancy termination once the diagnosis had
been made.
4
A subsequent meta-analysis based on four
randomized clinical trials with data on 15,935 women
(7992 were allocated to routine sonography vs. 7943 to
selective scanning) found the perinatal mortality rate was
significantly lower in patients allocated to routine scanning, again because of the early detection of fetal abnormalities that led to induced abortions.
20
The authors
concluded that routine ultrasound scanning is effective
and useful as a screening test for malformations.
Fetal Malformations:
Diagnostic Accuracy
BENEFITS OF ROUTINE SECOND-
TRIMESTER ULTRASOUND SCREENING
• More accurate gestational age
• Detection of major malformations before birth
• Earlier detection of multiple pregnancy
• Fewer low-birth-weight singleton births
• Lower incidence of induction for postterm
pregnancy
• Early detection of placenta previa
• Reassurance of a normal pregnancy
It can be difficult to interpret the results of studies
designed to assess the impact of routine screening.
4,11,16
Not only do anomalies need to be detected by ultrasound, but to show the benefit of ultrasound, there must
be a documented difference in outcome, either in termination of pregnancies, potentially leading to decreased
perinatal mortality from loss of anomalous fetuses, or
improved perinatal care. Because these studies do not
necessarily control for these outcomes, the benefit of
screening, in particular the importance of parental under-
The incidence of major congenital abnormalities at birth
in the general population is 2% to 3%, yet these abnormalities are responsible for 20% to 25% of perinatal
deaths and an even higher percentage of perinatal morbidity. Prenatal detection of an anomaly increases the
options for pregnancy management, and in select cases
the disorder may be amenable to intrauterine treatment.
For these reasons, offering routine ultrasound as a
screening test for congenital abnormalities is an attractive concept. However, the performance of screening
ultrasound in detecting abnormalities in the low-risk
population is variable, with sensitivity and specificity
ranging from 14% to 85% and 93% to over 99%,
respectively.
4,19,21-27
The wide range in sensitivity can be
partially explained by what authors used as the definition of an “anomaly” and the experience of the individuals performing and interpreting the studies.
factor is the type of anomaly. In the Eurofetus study,
the best detected abnormalities were of the urinary
system (88.5%) and central nervous system (88.3%).
Cardiac abnormalities were not well detected, whether
major (38.8%) or minor (20.8%), and the lowest rates
of detection were for minor abnormalities of the musculoskeletal system (18% vs. 73.6% for major defects)
and cleft lip and palate (18%).
28
Another important
19,26
Another
28
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