1. SON 2121 Obstetrical Sonography Part I
Lecture 9
Ultrasound Evaluation of Normal Fetal Anatomy
Holdorf

2. 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

3. The Diaphragm

4. 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.

5. The Liver

6. Spleen
Seen in the upper left abdomen posterior to the stomach, the spleen is echogenic and homogeneous.

7. The Spleen

8. 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.

9. Normal gut herniation

10. Omphalocele in the first trimester

11. 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.

12. The fetal chest

13. 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.

14. Normal Fetal lungs

15. 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

16. Normal 4 chamber heart view

17. 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 lungs

18. Fetal Circulation
Oxygenated blood centers the fetus through the umbilical vein
The 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.

19. 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.

20. Left ventricular Outflow Tract view
Identify origin of aorta from left ventricle
Sagittal 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 aorta

21. Definitions
LVOT
Extension of the ventricular cavity which connects to the Aorta.
RVOT
Extension of the ventricular cavity which connects to the pulmonary artery.

22. LVOT

23. left ventricular outflow tract view

24. RVOT

25. Right ventricular outflow tract view

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

27. 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

28. 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.

29. SPINE: Can be seen with great clarity especially after 22 weeks
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.

30. fetal C spine

31. Transverse Fetal C spine

32. Transverse Dorsal/Thoracic spine
The kidneys normally position themselves from Thoracic vertebra 12 (T-12) to Lumbar 2 (L-2)

33. Transverse D spine

34. Sagittal D/T spine

35. Sagittal/Transverse L/S spine

36. 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)

37. The choroid plexus in the lateral ventricles

38. The anatomy of the BPD

40. The cerebellum and cisterna/cistern magna (don’t be fooled)

41. The posterior fossa anatomy on one view

42. 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.

43. Left sided stomach- Position if scanning sagittal to mother?

44. This is NOT Normal Fetal Bowel

45. This is NOT normal Fetal bowel

46. Fetal Genitourinary System
Kidneys: The kidneys originate in the embryologic pelvis and migrate superiorly during gestation. They may be identified as early as 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.

47. Sagittal kidney at T12 – L2

48. Age-Related Renal Pelvis Measurements:
Weeks AP measurements 5mm
Weeks 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

49. Sagittal and transverse kidneys

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

51. Fetal Bladder

52. 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.

53. Adrenal Glands

54. Genitalia
Determination of the gender of a fetus may assist in the differential diagnosis of GU anomalies and or chromosomal syndromes.

55. Male

56. Female

57. Umbilical Cord Insertion

58. 3VC

60. Fetal Musculoskeletal System
By 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.

61. Fetal Hands

62. Fetal Feet

63. 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.

64. Facial Bones

65. 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.

66. Profile

67. 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.

68. Nuchal Fold

69. Image of the upper lip and nose

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

71. Fetal orbits

72. 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?

73. 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?

74. 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