This document provides a summary of embryonic development and fetal anatomy as assessed by ultrasound. It describes the normal development of the bilaminar embryo into a trilaminar embryo during gastrulation in the third week. It then discusses the folding and development of various organs over subsequent weeks, including the esophagus, stomach, small and large intestines, liver, gallbladder, pancreas, and anorectal region. It highlights various congenital anomalies that can be assessed prenatally using ultrasound, such as esophageal atresia, intestinal atresias or obstructions, anomalies of the biliary system and pancreas.

1. Faculty In Charge:
Dr. Vishal Gupta
Presented By:
Dr. Tarun Goyal

2. • By the end of the 2nd week of embryonic life, a bilaminar embryo has
developed with
o an epiblast (the layer facing the amniotic cavity) and
o a hypoblast (the layer facing the yolk sac) .
• Gastrulation at 3rd week of embryonic life, transforms this bilaminar
disk into a trilaminar embryo.
• Cells proliferate and migrate from the primitive streak (a thickened
band of cells on the epiblast) between the two layers, creating an
embryo with three definitive germ layers.
• The disk is then a mesoderm “sandwich” bordered above by ectoderm
and below by endoderm, except for two small areas on both ends
where the embryonic ectoderm and endoderm are in contact.
• These contact points are the oropharyngeal membrane (the future
mouth) at the cranial end and the cloacal membrane (the future
urogenital and anal orifices) at the caudal end.
EMBRYOLOGY

4. • At 4th week, Craniocaudal folding of the trilaminar disc creates the typical
C-shaped appearance seen at US; lateral folding closes the abdominal wall.
• The lateral edges (somatic mesoderm) move ventrally toward each other,
constricting the yolk sac and creating a coelomic space (future peritoneal
cavity) that separates the gut tube (gastrointestinal tract) from the body
tube (primary abdominal wall).
• The cloaca is the common chamber that is the precursor to the intestinal,
urinary, and genital tracts.
• A ventral diverticulum, the allantois, projects from the cloaca into the
connecting stalk (also called the body stalk), which attaches the embryo to
the chorionic mesoderm.
• During the 6th–7th weeks, the urorectal septum grows caudally and divides
the cloaca into the urogenital sinus anteriorly and the rectum posteriorly.
• When this division is complete, the cloacal membrane ruptures and creates
the external orifices.
• The urogenital sinus then undergoes further division to become the
bladder, urethra, and in females, a portion of the vagina.

6. • Umbilical cord forms from the connecting stalk, containing the
allantois. As the embryo grows and the amnion expands, the
connecting stalk lengthens.
• Physiologic gut herniation occurs during the 6th week, secondary to
inadequate space in the abdominal cavity for the rapidly growing
midgut.
• As the midgut grows and forms a U-shaped intestinal loop, it
herniates into the base of the umbilical cord . The midgut then
rotates 270° counterclockwise around the superior mesenteric
artery axis before it returns to the abdomen at 11–12 weeks .

8. Esophagus
• Extends from pharynx to the stomach.
• Collapsed and may therefore be difficult to visualize
• may be demonstrated as two or four echogenic lines representing
the esophageal walls
• Incomplete differentiation of the respiratory and GI tracts can
lead to esophageal atresia with or without tracheoesophageal
fistulas .
• The main sonographic signs of esophageal atresia include absent
or small stomach, polyhydramnios, and the esophageal pouch
sign (fluid collection in the blind end of the esophagus. At times a
distended oropharynx will be seen.
• Esophageal atresia is associated with additional anomalies . Half
of tracheoesophageal fistulas are part of the VACTERL Sequence.

9. Esophageal Atresia and Absent Stomach. (A) Transverse ultrasound through
the abdomen in a 25-week fetus shows no visible stomach. Polyhydramnios is
present; vertical pocket of amniotic fluid (X marks) measured >8 cm. Sp, Spine.
(B) Third-trimester fetus with absent stomach and polyhydramnios.

10. Esophageal Atresia. (A) Coronal view of upper thorax shows a
distended esophageal pouch (arrow).
(B) Coronal image through the neck in a 25-week fetus shows
distended oropharynx (arrows) secondary to esophageal
atresia.

11. Type Description Proportion
A EA without tracheoesophageal (TE) fistula 10%
B EA with TE fistula to the proximal
esophageal segment
<1%
C EA with TE fistula to the distal esophageal
segment
85%
D EA with TE fistula to both proximal and
distal esophageal segments
<1%
E TE fistula without esophageal atresia 5%

14. Stomach
• Seen as early as 7 weeks and should be noted routinely by 13 to 14
weeks’
• Stomach should be seen as a cystic structure in the left upper abdomen.
Normal Stomach. (A) In first
trimester the fetal stomach (St)
is an echolucent structure
below the diaphragm. (B) In
second trimester in sagittal
view, the stomach (St) is seen
below the diaphragm (Dia), and
the liver (L) extends anteriorly
to the abdominal wall.
(C) In second trimester in
transverse view of abdominal
circumference with the spine
to the left, the stomach is
superior

16. Dilated Fetal Stomach
• In second or third trimester a prominent or transiently dilated
fetal stomach may be seen on ultrasound.
• the diagnosis of a dilated fetal stomach requires that the stomach be
persistently dilated throughout a 30-minute assessment as well as
on successive examinations.
• The differential diagnosis of a dilated fetal stomach includes normal
variation in stomach size and GI atresia (e.g., duodenal atresia,
pyloric atresia) as well as pyloric stenosis.

17. Midline or Right-Sided Stomach
• Right-sided stomach should raise the possibility of heterotaxy syndrome,
characterized by an abnormal symmetry of the viscera and veins and is
associated with complex cardiac anomalies, intestinal malrotation, and
splenic (asplenia or polysplenia) and hepatic abnormalities.
• A midline stomach can represent intestinal malrotation.
Heterotaxy syndrome with
right-sided stomach.
Coronal T2-weighted fetal
magnetic resonance image
(MRI) at 34 weeks shows
left-sided liver and right-
sided stomach (St). The
cardiac apex (arrow) is
directed left. B, Bladder.

18. Small Bowel and Colon
In the first trimester and early in the second trimester, the small and large
bowel appear somewhat heterogeneous, with an echogenicity similar to
that of the liver. Later in pregnancy, fluid can be seen in the small bowel
loops, and meconium can be seen in the colon.
Bowel Obstruction
Duodenal Obstruction.
Duodenal stenosis or duodenal atresia is the most common
type of bowel obstruction in the fetus resulting from failure of
recanalization of the duodenal lumen, periampullary obstruction,
complete absence of a duodenal segment, or vascular ischemia.

19. • The sonographic appearance:
• presence of severe polyhydramnios (which may not be present until
the late second or third trimester) and the
• “double-bubble” sign, in which a second echolucent mass is
seen medial to the stomach bubble in a transverse view of
fetal abdomen .
• This sign is the result of the dilated segment of the duodenum proximal to
the atretic area and is highly suggestive of duodenal obstruction
• D/Ds:
• choledochal cyst,
• duodenal duplication cyst.
• transient double-bubble sign during the second trimester have
been reported, with normal outcomes.
• prominent incisura angularis of the stomach

20. Duodenal Atresia. (A) Oblique sagittal view through the fetal abdomen at 33
weeks shows the “double-bubble” sign of duodenal atresia with the fluid-filled
stomach (St) and duodenum (D). Ht, Heart. (B) Oblique coronal view shows
continuity (arrow) between the stomach and duodenum.

21. Jejunal and Ileal Obstruction.
• Etiology: early vascular compromise of the developing midgut.
This hypothesis is also supported by the association of
intestinal atresia with placental complications and other
abnormalities of vascular origin such as gastroschisis.
•
“Apple peel” jejunal atresia is a subtype that involves agenesis
of the mesentery, is more often familial.
• Cystic fibrosis is a common underlying cause of ileal
obstruction; the thick meconium associated with cystic fibrosis
can lead to ileal obstruction (meconium ileus) with or without
echogenic bowel.

22. • The prenatal diagnosis of jejunoileal obstruction is based on dilated
loops of bowel most frequently without a dilated stomach and
sometimes with hyperperistalsis.
•
If peristalsis is not observed, dilated small bowel can be difficult
to distinguish from dilated colon.
• The cutoff used to define dilated small bowel is greater than 7 mm
for loop diameter or greater than 13 mm for loop length.
• Polyhydramnios in cases of jejunoileal atresia is less common than in
cases of duodenal or esophageal atresia
• The more dilated loops visible, the more likely it is to be a distal or
ileal obstruction.

23. • Another sonographic sign associated with jejunoileal obstruction is
echogenic bowel, reflecting thickened meconium due to the intestinal
stasis. Ascites and abdominal calcifications can be seen in cases of
obstruction complicated by perforation
Jejunal and Ileal Atresia. (A) Jejunal atresia. Coronal image through the abdomen of a 30
week fetus shows several dilated loops of small bowel (arrows). (B) Ileal atresia. Transverse
fetal abdomen with multiple dilated loops of bowel. The bowel lumen is measured in the
largest transverse diameter (calipers

24. Meconium Ileus
• It is the obstruction of the ileum by thickened meconium.
• Some cases are associated with cystic fibrosis, but only a minority (up to
20%) of cases of cystic fibrosis will present with meconium ileus during
pregnancy.
• The presence of echogenic bowel in addition to the general sonographic
signs of bowel obstruction increases the likelihood of meconium ileus.
Echogenic Bowel
• refers to increased brightness of the fetal bowel at the time of ultrasound
examination.
• echogenicity that is similar or greater than that of adjacent bone, such as
the iliac bone.
• requires that the lowest level of ultrasound gain at which bones still
appear white be used and that all image enhancement algorithms be
disabled

27. Meconium Peritonitis and Pseudocyst
• It is in utero bowel perforation that is followed by leakage of
meconium into the peritoneal cavity, leading to chemical irritation
and inflammatory response.
• Sonographic Appearance:
• abdominal calcifications ( calcification of the peritoneum
outlining bowel or liver)
• ascites
• echogenic bowel, dilated bowel, and polyhydramnios.
• meconium pseudocyst which is characterized by a cyst encircled
by an echogenic rim.

28. Anorectal Malformations
• Malformations ranges from isolated imperforate anus to more complex
cloacal malformations.
• They are classified as low (majority), intermediate, and high based on
whether the bowel ends below, at the same level, or above the level of
the levator ani muscle, respectively.
• Anal atresia is also part of the VACTERL sequence and is associated
with a large number of genetic syndromes.
• The main sonographic sign is dilated loops of small or large bowel.
Polyhydramnios is absent in the majority of cases.
• Inability to visualize the anal mucosa on transverse transperineal view
(known as the anal dimple, which is the result of the echogenic mucosa
surrounded by the hypoechoic muscle of the anal sphincter) has been
suggested as an important sonographic marker in cases of imperforated
anus.

29. Normal Colon and Anal Dimple. (A) Normal third-trimester large bowel. Transverse image
through the abdomen at 37 weeks shows prominent meconium-filled loops of colon. This is
normal in the third trimester and should not be taken to indicate bowel obstruction. RK,
Right kidney; Sp, spine.
(B) Although not part of standard scan guidelines, the anal dimple (arrow) can easily be
demonstrated on a transverse plan through the perineum. Visualization of the dimple excludes
anal atresia.

30. Hirschsprung Disease
• A congenital disorder of the colon caused by absence of ganglia in
the distal colon, thereby leading to functional colonic obstruction.
• The diseased segment usually involves the most distal part of the
colon, including the internal anal sphincter, and extends proximally
to involve variable portions of the colon, with the most severe
forms involving the whole colon.
• The sonographic signs in these cases are nonspecific and include
bowel dilatation, polyhydramnios, and echogenic bowel with most
common sign being failure to pass meconium.

32. Liver
Hepatomegaly
• Hepatomegaly is associated with a variety of conditions including
fetal hemolytic anemia which results in a compensatory increase in
hematopoiesis within the liver.
• Hepatomegaly has also been associated with trisomy 21, possibly
because of the abnormal myelopoiesis in these fetuses
Hepatic Calcifications
• can be single or multiple
• The pathophysiology of hepatic calcifications in otherwise normal
fetuses is unknown, and in the majority of cases, such calcifications
represent an isolated finding and have no clinical consequence

33. Hepatomegaly
Hepatic calcifications

34. Hepatic Cysts and Masses
• hepatic masses are hypoechoic or cystic and may include hepatic cysts,
hemangiomas and abnormal myelopoiesis in fetuses with trisomy 21.
• Solid echogenic masses may be identified, which may represent
benign lesions such as hamartoma (which may have a cystic or mixed
cystic-solid appearance) and adenoma, as well as malignant lesions as
hepatoblastoma.
• Vascular hepatic lesions include congenital hemangiomas and
hepatoblastomas, but most hemangiomas are small and appear
avascular on color Doppler ultrasound.
• Such vascular lesions, especially when of large size, may lead to high-
output cardiac failure and hydrops, and fetal anemia and
thrombocytopenia (Kasabach-Merritt sequence).

35. Gallbladder and Biliary System
The normal fetal gallbladder is an oblong, echolucent structure in the
anterior liver, generally located 45 degrees to the right of midline
and inferior to the umbilical vein.
Nonvisualization of the Gallbladder
• Associated with gallbladder agenesis/atresia, cystic fibrosis,
aneuploidy and biliary atresia.
• Extrahepatic biliary atresia is a rare congenital disorder. It is a
single leading cause for liver transplantation during childhood.
The diagnosis of extrahepatic biliary atresia should be considered
whenever the gallbladder cannot be visualized.

37. Fetal Gallstones
• Echodensities in the fetal gallbladder can represent either
sludge or gallstones and are most commonly seen in the third
trimester.
• Gallstones may produce acoustic shadowing

38. Pancreas
• Visualization of the pancreas is often not possible at the time of the second-
trimester anatomy scan.
Annular Pancreas
• rare developmental anomaly that accounts for 1% of neonatal intestinal
obstructions.
• The annular tissue in these cases has been suggested to originate from the
ventral pancreatic bud.
• Annular pancreas is considered in the differential diagnosis of a dilated
duodenum or the double-bubble sign.
Pancreatic Cysts
• a rare congenital abnormality originating from the pancreatic duct and may
appear as a single cystic or multicystic mass.
• Pancreatic cysts may be idiopathic but also have been associated with
BeckwithWiedemann syndrome, polycystic kidney disease, and von
Hippel–Lindau disease.

39. Annular Pancreas. (A) Transverse image at 28 weeks shows a dilated
proximal duodenum (arrowheads) in direct continuity with the stomach
(St). (B) Coronal T2 weighted MRI at 32 weeks confirms dilated duodenum.

40. Spleen
• visualized in the left upper abdomen, lateral to the spine and superior
to the left kidney. Nomograms are available for splenic size from 18
weeks until term.
• Asplenia or polysplenia are associated with heterotaxy syndromes.
Splenomegaly
Splenomegaly is associated with conditions similar to those associated
with hepatomegaly, hemolytic fetal anemia, fetal infections, metabolic
and storage disorders, trisomy 21 and Beckwith-Wiedemann syndrome.
Splenic Cysts
Fetal splenic cysts are rare, usually benign, and are associated with overall
good prognosis. These cysts may regress spontaneously, in some cases
they are complicated by infection, rapid growth, rupture, and/or bleeding.

43. Gastroschisis
It is a relatively small (<4 cm in most cases), full thickness paraumbilical defect of the
abdominal wall, most often located to the right of the umbilicus.
Free-floating loops of bowel in the amniotic fluid are the key finding on ultrasound.
Prenatal Diagnosis
• The free-floating loops of bowel are identified intraamniotically; in these cases the
diagnosis can already be made as early as the first trimester. Most often the defect is
located at the right paraumbilical region.
• The free-floating bowel has a characteristic cauliflower-like appearance. The bowel
may appear echogenic due to edema and inflammation of the wall secondary to long
standing exposure to amniotic fluid.
• The stomach is often displaced downward within the abdominal cavity. The umbilical
cord inserts normally into the abdomen, adjacent to but separate from the defect.

44. Gastroschisis.
(A) Schematic of the full-
thickness abdominal wall
defect lateral to the umbilical
cord.
(B) Transverse color Doppler
image at the level of the
abdominal umbilical cord
insertion (arrow) in a 20-week
fetus shows free-floating loops
of bowel (arrowheads) in the
amniotic fluid to the right of
the cord insertion site. B,
Bladder; Sp, spine.
(C) Sagittal view of a fetus
with gastroschisis with bowel
(arrow) visible between the
legs.
(D) Gastroschisis with dilated
intraabdominal loops of small
bowel (SB).
E) Gastroschisis with dilated
loops of bowel floating in
the amniotic fluid.

45. Omphalocele
Omphalocele refers to herniation of the intestine and other abdominal
organs into the base of the umbilical cord through an enlarged umbilical
ring, with the umbilical cord inserting at the apex of the herniated sac. The
herniated content is covered by amnion and peritoneum.
Prenatal Diagnosis
• In the first trimester, physiologic midgut herniation can be mistaken for
an omphalocele. It should resolve by 12 weeks.
• It should never include the liver, and the herniation should not be more
than 1 cm into the cord.
• The presence of even small herniation into the base of the umbilical
cord beyond 12 weeks is therefore diagnostic of omphalocele.
• In cases of large defects, the omphalocele may contain other organs
such as liver and stomach.
• The umbilical cord can be seen inserted on the herniated sac rather than
directly to the abdominal wall.

46. Small Omphalocele.
(A) Schematic of membrane
covered omphalocele
containing only bowel.
(B) Transverse image of
abdomen with loop of
bowel herniated into base
of umbilical cord. The fetus
had trisomy 18.
(C) Transverse image of
abdomen at 26 weeks
shows a bowel-only
omphalocele (arrow). The
umbilical cord
(arrowheads) inserts onto
the membrane, which
covers the defect. Sp,
Spine.
(D) Transverse color Doppler image at 26 weeks shows a
bowel-only omphalocele (arrow). The umbilical vessels
(arrowheads) course around the bowel, in the
membrane that covers the defect. Sp, Spine

47. Associated Conditions
• The most common aneuploidies are trisomies 13 and 18.
• Cases where the liver is found in the omphalocele are less likely
to be associated with chromosomal abnormalities.
• Omphalocele is associated with several single gene mutation
syndromes (including autosomal dominant, autosomal recessive,
and X-linked recessive disorders), and Beckwith-Weidemann
syndrome.
Beckwith-Weidemann syndrome is associated with
omphalocele, macroglossia, and overgrowth
• Associated structural abnormalities are common and include
midline defects (cardiac, cleft lip and palate, and spinal/vertebral
anomalies), clubfoot, and central nervous system anomalies.

50. Beckwith-Wiedemann Syndrome.
(A) Coronal oblique ultrasound at 28 weeks shows the right kidney measuring 6.9 cm, well
above the 95th percentile. The adjacent liver (arrows) extends beyond the renal margins
indicating that it is enlarged as well. Visceromegaly is part of Beckwith-Wiedemann
syndrome.
(B) Three-dimensional surface rendered view of the fetal face in the same case shows
macroglossia (arrow).

51. Bladder Exstrophy
• It refers to infraumbilical abdominal wall defect that results from
incomplete closure of the lower abdominal wall and the anterior wall of
the bladder.
• Diagnosis of bladder exstrophy is mainly based on the inability to
visualize the bladder. The exposed bladder mucosa may become
inflamed and thickened and may therefore appear as an irregular
contour of the lower anterior abdominal wall
• Another clue for the diagnosis is caudal displacement of the umbilical
cord insertion site.
• Associated anomalies include genital abnormalities such as epispadias,
a combination known as bladder exstrophy– epispadias complex.

54. Cloacal Exstrophy
• It is a more complex multisystem abdominal wall defect that affects all
the components of the cloaca (bladder and urethra, genitalia and
rectum), as well as lower spine.
• Cloacal exstrophy is often termed OEIS complex (omphalocele-
exstrophy– imperforate anus–spinal dysraphism).
• The pathogenesis has been attributed to premature rupture of the
cloacal membrane or to very early defect in the closure of the ventral
body wall.
• It occurs at a higher rate in monozygous than in dizygous twins,
suggesting a vascular component.

55. • The prenatal diagnosis is based on the combination of omphalocele,
inability to visualize the bladder and anal dimple, and the presence
of spine anomalies such as meningomyelocele or tethered cord.
• Additional findings may include genital abnormalities (e.g.,
epispadias), single umbilical artery, renal abnormalities and ascites.
• A unique sonographic sign is the “elephant trunk,” which is the
result of a prolapsed loop of bowel between the two halves of the
open bladder.
• Diagnosis of OEIS has been reported as early as 13 weeks.
• Diagnostic difficulties can occur in differentiating this disorder from
other complex abdominal wall defects including limb–body wall
complex and pentalogy of Cantrell.

57. Illustration shows the
typical
“elephant trunk”
appearance due
to extrusion of bowel
loops between the
everted halves of the
bladder.

58. Ectopia Cordis
• a midline defect of the upper fetal ventral body wall through which
all or part of the heart extrudes, with or without a membrane.
• Most commonly the heart protrudes at the level of the chest
through a defect involving the sternum, but the heart can be located
at the cervical or abdominal region.
• Association with structural cardiac anomalies or other abdominal
wall defects is common.
• Trisomy 18 has been associated with this diagnosis, especially in the
presence of additional abnormalities.
Transverse image through the chest on one of a
dichorionic twin pair shows that the liver and
heart (arrow) are external to the thorax. Sp,
Spine. This is a lethal malformation, in this case,
caused by amniotic bands, which were visible in
real time. The co-twin was normal and was
delivered at term.

59. Pentalogy of Cantrell
• A rare complex disorder of the ventral body wall that refers to a
combination of defect of the sternum, ectopia cordis, cardiac
anomalies (e.g., septal defects, tetralogy of Fallot, transposition of
great arteries), defect of the anterior diaphragm and diaphragmatic
pericardium, and supraumbilical abdominal wall defect (most
commonly omphalocele).
• Other associated
anomalies include
midline
abnormalities such
as facial cleft and
encephalocele.
Association with
trisomies 18 and 13
is also noted.

60. Body Stalk Anomaly
• Also known as limb–body wall complex, a rare and lethal disorder of
the anterior abdominal wall.
• Three hallmarks of this disorder:
1. There is a severe disruption of the abdominal and thoracic walls.
2. The abdominal and thoracic organs (e.g., heart, lungs, liver,
bowel, bladder) are located outside the body cavity and are
contained within a sac that is closely attached to the placenta,
leading to a relatively fixed position of the fetus.
3. The umbilical cord is very short or absent, possibly because of a
failure of the body stalk to develop properly.
• Associated musculoskeletal abnormalities are common and include
severe kyphoscoliosis and limb defects such as club foot and absent
or malformed limbs.
• Pathogenesis includes early vascular disruption, disruption due to
amniotic bands following early amniotic rupture, or complete failure
of the folding process of the embryonic disc.

63. Amniotic Band Syndrome (Abdominoschisis)
• Amniotic band syndrome can affect any part of the fetus.
• The defect can appear similar to that of gastroschisis, with
the abdominal and/or thoracic organs floating freely
within the amniotic cavity with no sac
around them.
• The diagnosis of amniotic band syndrome is suggested by
the demonstration of the amniotic bands and the presence
of additional findings that are associated with disruption
due to amniotic bands including limb defects (constriction
or amputation of a limb), encephalocele, and facial clefts.
• Unlike body stalk anomaly, the umbilical cord can be
demonstrated in these cases
.

64. • The US findings for amniotic band syndrome are highly variable,
depending on which body part is involved and the gestational
age at which the insult occurs.
• Craniofacial and visceral defects result from amnion rupture
within the first 45 days of life.
• Craniofacial abnormalities include atypical encephalocele and
facial cleft, and limb defects range from constriction bands to
amputation; both abdominoschisis and thoracoschisis. The
defects involved in amniotic band syndrome occur in a non-
anatomic distribution and are sometimes described as “slash
defects.”