Download Obstetrical Sonography 1. Lecture 9 Survey of Normal Fetal Anatomy

SON 2121
Obstetrical Sonography Part I
Lecture 9
Ultrasound Evaluation of Normal Fetal Anatomy
Holdorf
Normal Fetal Abdomen and Abdominal Wall
 Diaphragm
 The superior aspect of the abdomino-pelvic cavity is defined by
the diaphragm muscle.
 It appears sonographically as a hypoechoic curved line
separating the more echogenic lungs from the liver and stomach
The Diaphragm
 Liver
 The left lobe is larger than the right in the fetus. The liver
should appear homogeneous sonographically. The fluid-filled
gallbladder is seen in the anterior right abdomen, inferior to the
liver margin.
The Liver
 Spleen
 Seen in the upper left abdomen posterior to the stomach, the
spleen is echogenic and homogeneous.
The Spleen
 Abdominal Wall
 Development of the anterior abdominal wall involves normal
herniation of the viscera into the base of the umbilical cord
during the first trimester. After undergoing midgut rotation, the
contents return to the abdominal cavity, usually by the 12th
week, but no later than the 14th week of gestation. Evaluation of
the anterior abdominal wall should be done after this time.
Normal gut herniation
Omphalocele in the first trimester
Fetal Chest and Cardiovascular System
Thorax
 Axial and coronal sections demonstrate integrity of thorax, fetal
breathing movements, and overall size and shape. The fetal heart
occupies approximately 1/3 of the thoracic cavity.
The fetal chest
Lungs
 Coronal section demonstrates relationships of pulmonary
parenchyma to heart and chest wall. The lung parenchyma is
homogeneous and slightly more echogenic than the liver.
Normal Fetal lungs
Fetal Echocardiography
 Four Chamber view: The four chamber view is the SINGLE MOST
important image of the fetal heart. Adequate imaging is essential,
and normal features include:
 Apex of heart points 45 degrees to left anterior chest wall
 Ventricles approximately same size
 Flap of foramen ovale opens into left atrium
 Prominent moderator bands present in apex of right ventricle
 Valves separate both atria from ventricles
Normal 4 chamber heart view
 Blood flow through the heart is proportioned as follows:
 60% of right atrial blood passes through the foramen ovale, into the
left atrium, and eventually to systemic circulation.
 40% of right atrial blood enters the right ventricle. Of this, right
ventricular output is as follows:
o 92% of main pulmonary artery volume bypasses the lungs via the
ductus arteriosus and into systemic circulation.
o 8% of right ventricular bold reaches the lungs
Fetal Circulation
 Oxygenated blood centers the fetus through the umbilical vein
 The ductus venosus partially bypassed the liver to send oxygenrich blood to the right atrium.
 The foramen ovale shunts some of the right atrial blood directly
the left atrium
 The ductus arteriosus allows oxygen-rich blood from the
pulmonary artery into the aortic arch to circulate throughout the
fetus.
Definitions
Foramen ovale: Allows blood to enter the left atrium from the
right atrium. It is one of two fetal cardiac shunts, the other
being the ductus arteriosus…In most individuals, the
foramen ovale closes at birth.
Ductus arteriosus: Allows blood that still escapes into the right
ventricle to bypass the pulmonary circulation.
Ductus venosus: Shunts most of the left umbilical vein blood
flow directly to the IVC, bypassing the liver.
 Left ventricular OutflowTract view
 Identify origin of aorta from left ventricle
 Sagittal section shows aorta arch and its branch
 RightVentricular Outflow tract view
 Identify origin of pulmonary trunk from right ventricle
 Correct orientation of pulmonary trunk is “draping” anterior to
the aorta when seen in cross-section
 Diameter of pulmonary artery is 9% larger than that of the aorta
Definitions
 LVOT
 Extension of the ventricular cavity which connects to the Aorta.
 RVOT
 Extension of the ventricular cavity which connects to the
pulmonary artery.
LVOT
left ventricular outflow tract view
RVOT
Right ventricular outflow tract view
fetal circulation - the foramen ovale, ductus arteriosus, and the ductus
venosus.
Fetal Central Nervous System
Embryology
 Neurulation begins with the formation of the neural plate, then the
neural folds, and the ultimate fusion and closure as the neural tube.
 Neural plate- thickening of embryonic ectoderm and adjacent
mesoderm.
 Neural groove-an invagination of the neural plate along its central
axis.
 Neural folds-thickening of the neural plate lateral to the neural
groove. These folds continue to thicken and grow toward the
midline until they meet and fuse leaving both ends open.
 Neural tube-fused neural folds
Spine
 Real-time examination is performed in at least 2 orthagonal planes
of section.
 Transversely, the exam is begun in the proximal cervical spine and
proceeds caudally. Attention is paid to the location and configuration
of the ossification centers in each vertebra, the integrity of the
musculature in the back and the integrity of the skin line.
 Sagittally or coronally, the spine is examined to assess: Cervical and
lumbosacral curvatures, sacral caudal tapering, and configuration of
vertebral ossification centers.
SPINE: Can be seen with great clarity especially after 22 weeks.
Transverse imaging offers the best method of evaluation.
Composed of three ossification centers-two posterior and
one anterior. On longitudinal view, the posterior elements
are seen as parallel structures.
fetal C spine
Transverse Fetal C spine
Transverse Dorsal/Thoracic spine
 The kidneys normally position themselves from Thoracic
vertebra 12 (T-12) to Lumbar 2 (L-2)
Transverse D spine
Sagittal D/T spine
Sagittal/Transverse L/S spine
Brain
 Axial sections are obtained at multiple levels through the cerebral
hemispheres. The following structures are documented: Cavum
septum Pellucidum, both lateral ventricles (when possible) Thalami,
and Choroid Plexus.
 Measurements are taken of the Atrium of the lateral ventricle
(normal is < 10 mm)
 Biparietal diameter (BPD) and Head Circumference (HC)
 Oblique axial sections are obtained through the posterior fossa, and
the following anatomical structures are documented: Cerebellum,
Brain stem, Cistern magna is measured (normal is > 3 and < 11
mm)
The choroid plexus in the lateral
ventricles
The anatomy of the BPD
The cerebellum and cisterna/cistern magna (don’t be fooled)
The posterior fossa anatomy on one
view
Fetal Gastrointestinal System
 Esophagus: Difficult to image unless fetus is swallowing or there is
stenosis
 Stomach: On transverse view, it is seen as an ovoid/spherical fluid
collection in upper left abdomen. Coronal imaging can demonstrate
the fundus, body, and pylorus. The muscular layer is very thin in
normal fetuses and may be thickened in hypertrophic pyloric stenosis.
 Intestines: Difficult to isolate specific segments unless there is
sufficient fluid content to provide sonographic contrast. The intestines
are normally mixed echogenicity to cystic in appearance. Peristalsis
should be seen by late second trimester. Meconium (a mixture of bile
and swallowed vernix, desquamated epithelium, and fetal hair)
become packed in the large bowel and may appear as highly echogenic
areas within the bowel. The colon is often most obvious in the late
third trimester.
Left sided stomach- Position if scanning sagittal to mother?
This is NOT Normal Fetal Bowel
This is NOT normal Fetal bowel
Fetal Genitourinary System
 Kidneys: The kidneys originate in the embryologic pelvis and
migrate superiorly during gestation. They may be identified as
early as 12-14 weeks as two relatively sonolucent structures
adjacent to the spine in transverse section. Echo poor renal
pyramids are distributed evenly throughout the parenchyma.
Renal sinus fat is more echogenic and can be seen in the hilum of
each kidney. Occasionally the renal pelvis may contain a small
amount of fluid. This is a normal finding, and does not indicate
obstructive uropathy; it is seen in 18% of fetuses after 24 weeks.
Sagittal kidney at T12 – L2
 Age-Related Renal Pelvis Measurements:
 Weeks 13-20 AP measurements 5mm
 Weeks 20-30 AP measurements 8mm
 Weeks 30-term AP Measurements 10mm
 AP renal Pelvis measurements
 Less than or equal to 5mm is normal
 5-10mm is probably normal, needs follow-up
 Greater than or equal to 10mm / 85% have anatomic anomaly
Sagittal and transverse kidneys
 Bladder
 The fetal urinary bladder can be identified routinely by 20 weeks. Its
presence is an important indicator of active renal function.
Transversely, the iliac wings are important landmarks. The bladder is
a dynamic structure that empties and fills in the normal fetus in 3045 minute cycles. Absence on the first sonogram does not indicate
abnormality.Wait 30 minutes and re-scan.
Fetal Bladder
 Adrenal Glands
 The adrenal glands are relatively large in the fetus. 90% is cortex,
which quickly involutes after birth. The adrenals are seen as oval
masses of echo-poor tissue lying superior to the kidneys on Sagittal
scan. Transversely, they appear as long, thin echogenic lines of
medulla surrounded by thicker sonolucent rims of cortex. Adrenal
glands should be smaller than the normal kidney. Care should be
taken to identify normal kidneys so renal agenesis is not missed.
Adrenal Glands
 Genitalia
 Determination of the gender of a fetus may assist in the
differential diagnosis of GU anomalies and or
chromosomal syndromes.
Male
Female
Umbilical Cord Insertion
3VC
Fetal Musculoskeletal System
 By 15-16 weeks most bones can be imaged. The ossification
center is visualized, not the entire structure, which contains
cartilaginous tissue.
 Appendicular Skeleton (long bones)
 Images well by early-mid second trimester. Extremely long
bones are easily seen including metacarpals, metatarsals and
phalanges. Carpals are not ossified until after birth, therefore
they are not seen. An exception is the calcaneus, which ossifies
between the fifth and sixth month.
 The scapulae and clavicles can be seen.
Fetal Hands
Fetal Feet
 Axial Skeleton (cranium, facial bones, pelvis spine)
 In addition to the cranial bones, the sphenoid bone and petrous
ridges are seen at the base of the skull, separating the cranial
fossae.

 Facial bones include orbits, maxilla, mandible and boney nasal
septum

 PELVIS: iliac ossification centers are seen from early second
trimester. Ischial ossification centers are seen at about 20 weeks.
Facial Bones
Fetal Face and Neck
 Face: The upper lip may be visualized in an oblique coronal plane
and is useful in searching for facial clefts and some types of
proboscis.
 Eyes: The eyes may be imaged in either a true coronal or a
transverse plane. Measurement of the outer orbital distance is
valuable in diagnosing hypertelorism or hypotelorism. Inner
orbital distance measurements may also be used.
Profile
Neck: Soft tissue structures of the neck may be evaluated in both
Sagittal and transverse planes. Special attention should be paid to
surface contours since soft tissue masses may cause protrusion.
Transverse sections allow the measurement of the nuchal fold.
Studies have shown an association with Down syndrome when
this measurement exceeds 6 mm when measured between 15
and 21 weeks.
Nuchal Fold
Image of the upper lip and nose
image of the soft palate. How deep is
the cleft? Volmer?
Fetal orbits
FINAL THOUGHTS Measurements
 Perform your measurements in an orderly fashion.
 List the order:
 CRL, MSD for first trimester
 BPD, HC, AC, FL for second and third trimester
 Show images of the measurements as to how you want them
taken.
 3 of each? Both femurs?
Final Final thoughts
 How about the placenta?
 How about the amniotic fluid?
 How about the cervix?
 How about the uterus and ovaries (fibroids, cysts?)
 How about the ears?
 How long will you allot for a full OB scan…40 min?
Final Final Final thoughts
 So what IS your protocol?
 General survey first? Fluid, Placenta, Lie, Viability
 Measurements?
 Anatomy
 Head
 Chest
 Abdomen
 Pelvis
 Spine
 Arms
 Legs
REPORT