Lecture 9 Ultrasound Evaluation of Normal Fetal Anatomy - PowerPoint Presentation

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Lecture 9Ultrasound Evaluation of Normal Fetal AnatomyHoldorf

SON 2121

Obstetrical Sonography Part ISlide2

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 stomachSlide3

The DiaphragmSlide4

LiverThe 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.Slide5

The LiverSlide6

SpleenSeen in the upper left abdomen posterior to the stomach, the spleen is echogenic and homogeneous.Slide7

The SpleenSlide8

Abdominal WallDevelopment 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 14

th

week of gestation. Evaluation of the anterior abdominal wall should be done after this time.Slide9

Normal gut herniationSlide10

Omphalocele in the first trimesterSlide11

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.Slide12

The fetal chestSlide13

LungsCoronal section demonstrates relationships of pulmonary parenchyma to heart and chest wall. The lung parenchyma is homogeneous and slightly more echogenic than the liver.Slide14

Normal Fetal lungsSlide15

Fetal EchocardiographyFour 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 ventriclesSlide16

Normal 4 chamber heart viewSlide17

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:

92% of main pulmonary artery volume bypasses the lungs via the ductus arteriosus and into systemic circulation.

8% of right ventricular bold reaches the lungsSlide18

Fetal CirculationOxygenated blood centers the fetus through the umbilical veinThe ductus venosus partially bypassed the liver to send oxygen-rich 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.Slide19

DefinitionsForamen 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.Slide20

Left ventricular Outflow Tract viewIdentify origin of aorta from left ventricleSagittal section shows aorta arch and its branch

Right Ventricular 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 aortaSlide21

DefinitionsLVOTExtension of the ventricular cavity which connects to the Aorta.

RVOT

Extension of the ventricular cavity which connects to the pulmonary artery.Slide22

LVOTSlide23

left ventricular outflow tract viewSlide24

RVOTSlide25

Right ventricular outflow tract viewSlide26

fetal circulation - the foramen ovale, ductus arteriosus, and the ductus venosus.Slide27

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 foldsSlide28

SpineReal-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.Slide29

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.Slide30

fetal C spineSlide31

Transverse Fetal C spineSlide32

Transverse Dorsal/Thoracic spineThe kidneys normally position themselves from Thoracic vertebra 12 (T-12) to Lumbar 2 (L-2)Slide33

Transverse D spineSlide34

Sagittal D/T spineSlide35

Sagittal/Transverse L/S spineSlide36

BrainAxial 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)Slide37

The choroid plexus in the lateral ventriclesSlide38

The anatomy of the BPDSlide39
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The cerebellum and cisterna/cistern magna (don’t be fooled) Slide41

The posterior fossa anatomy on one viewSlide42

Fetal Gastrointestinal SystemEsophagus: 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.Slide43

Left sided stomach- Position if scanning sagittal to mother?Slide44

This is NOT Normal Fetal BowelSlide45

This is NOT normal Fetal bowelSlide46

Fetal Genitourinary SystemKidneys: 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.Slide47

Sagittal kidney at T12 – L2Slide48

Age-Related Renal Pelvis Measurements:Weeks 13-20 AP measurements 5mmWeeks 20-30 AP measurements 8mmWeeks 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 anomalySlide49

Sagittal and transverse kidneysSlide50

BladderThe 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 30-45 minute cycles. Absence on the first sonogram does not indicate abnormality. Wait 30 minutes and re-scan.Slide51

Fetal BladderSlide52

Adrenal GlandsThe 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.Slide53

Adrenal GlandsSlide54

GenitaliaDetermination of the gender of a fetus may assist in the differential diagnosis of GU anomalies and or chromosomal syndromes. Slide55

MaleSlide56

FemaleSlide57

Umbilical Cord Insertion Slide58

3VCSlide59
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Fetal Musculoskeletal SystemBy 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.Slide61

Fetal HandsSlide62

Fetal FeetSlide63

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.Slide64

Facial BonesSlide65

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.Slide66

ProfileSlide67

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.Slide68

Nuchal FoldSlide69

Image of the upper lip and noseSlide70

image of the soft palate. How deep is the cleft? Volmer?Slide71

Fetal orbitsSlide72

FINAL THOUGHTS MeasurementsPerform 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? Slide73

Final Final thoughtsHow 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?Slide74

Final Final Final thoughtsSo what IS your protocol?

General survey first? Fluid, Placenta, Lie, Viability

Measurements?

Anatomy

Head

Chest

Abdomen

Pelvis

Spine

Arms

Legs

REPORT