The Fetal Gastrointestinal System

The fetal gut develops at the end of the fifth menstrual week and can be divided into the

foregut, midgut, and hindgut

The esophagus may be visualized when needed as

several parallel echogenic lines within the thorax

the fetal stomach can be visualized as early as 8 weeks’ gestation, but most certainly should be seen by

14 weeks in the left upper quadrant as an anechoic, circular organ.

The diameter of small bowel is

smaller than the colon and does not typically exceed 5 mm

abdominal circumference

axial view of the fetus and should include the fetal stomach, transverse thoracic spine, and intrahepatic portion of the umbilical vein and its junction with the left portal vein

abdominal diameter

AC = 1.57 × (AD1 + AD2).

What is Polyhydramnios

excessive amniotic fluid,

AFI > 24 cm

DVP >8CM

in later gestation, somewhere around 9 weeks, the fetal kidneys begin to produce urine, a liquid that eventually comprises

most of the amniotic fluid.

The fluid passes through the esophagus, into the stomach, and travels through

the small bowel and into the colon, where absorption takes place

Polyhydramnios results when there is an

obstruction or disturbance to the normal flow and absorption of amniotic fluid. Consequently, there is a buildup of amniotic fluid resulting from the continual production of urine by the fetal kidneys

The congenital absence of part of the esophagus is termed

esophageal atresia

Consequently, the esophagus and the trachea often form an abnormal connection known as a

tracheoesophageal fistula (90% of the time)

Esophageal Atresia is associated with

duodenal atresia, VACTERL association, trisomy 21, intrauterine growth restriction, and trisomy 18/edward (E FOR EDWARDS).

Sonographic Findings of Esophageal Atresia

Absent or small stomach

Polyhydramnios

Intrauterine growth restriction

The congenital maldevelopment or absence of the proximal portion of the small bowel, the duodenum, is termed

duodenal atresia

Duodenal atresia classically presents sonographically as a

dilated, fluid-filled anechoic stomach and an anechoic fluid-filled proximal duodenum, offering the “double bubble” sign

Duodenal atresia has a proven association with

trisomy 21; thus, additional sonographic markers of trisomy 21 should be aggressively investigated during the examination.

Also esophageal atresia, VACTERL association, intrauterine growth restriction, and cardiac anomalies.

Sonographic Findings of Duodenal Atresia

“Double bubble” sign

Polyhydramnios

Intrauterine growth restriction

It is essential to remember that in the fetus, the left lobe of the liver is typically

larger than the right lobe

What is the most common abnormality of the fetal liver.

hepatomegaly

Hepatomegaly may occur as a result of

intrauterine infections, fetal anemia (Rh incompatibility), or be seen with Beckwith–Wiedemann syndrome.

Enlargement of the fetal spleen—splenomegaly—can accompany hepatomegaly and may be suggestive of

intrauterine infections or Rh incompatibility with hydrops

Fetal gallstones (cholelithiasis) and sludge within the gallbladder may be noted in utero, most often in the third trimester. Gallstones appear sonographically as

echogenic foci in the right upper quadrant of the fetus that may or may not produce posterior shadowing

An additional rare abnormality of the biliary tree is the

choledochal cyst

There are four different types of choledochal cysts, with the most common being described as the

cystic dilatation of the common bile duct.

Choledochal cysts can lead to

cholangitis (swelling of bile duct) , portal hypertension, pancreatitis, and liver failure.

In general, the echogenicity of the small intestine should not be

isoechoic to or greater than that of fetal bone

if a higher frequency transducer suggests echogenic bowel, that the sonographer should

decrease the frequency to 5 MHz or less and decrease the overall gain

Echogenic bowel has been linked with

trisomy 21, cystic fibrosis, growth restriction, fetal demise, congenital infections such as cytomegalovirus, and gastrointestinal obstructions.

what is Hirschsprung disease and what is it caused by

a functional fetal bowel obstruction, is caused by the absence of nerves within the bowel wall.

Hirschsprung disease is more common in

males

Hirschsprung disease has a strong association with

trisomy 21

The sonographic finding of dilated loops of bowel within the fetal abdomen is indicative of

a fetal bowel obstruction.

These dilated loops of bowel should not exceed

7 mm in diameter or measure greater than 15 mm in length

Obstruction of the fetal bowel most often occurs when there is a meconium plug causing the barrier, a condition referred to as

meconium plug syndrome.

The most common type of colonic atresia that will lead to a bowel obstruction is

anorectal atresia

Anorectal atresia may be linked with

VACTERL association and chromosomal abnormalities

Anorectal atresia will most often lead to the visualization of a

dilated fetal rectum.

what are the two of the most common ventral abdominal wall defects

Gastroschisis and omphalocele

it is important to note that MSAFP levels have been shown to be much higher in gastroschisis than in

omphalocele.

As a part of normal fetal development during the first trimester, the midgut herniates into the base of the umbilical cord; this is termed

physiologic bowel herniation

The intestines return to the abdomen by the

12th gestational week.

Gastroschisis is the

herniation of abdominal contents through a right-sided, periumbilical abdominal wall defect

Gastroschisis is thought to be caused by a vascular incident occurring to either the

right umbilical vein or the omphalomesenteric artery

Gastroschisis, unlike omphalocele,

does not have a strong association with chromosomal abnormalities

Clinical Findings of Gastroschisis

Elevated MSAFP

Sonographic Findings of Gastroschisis

Normal cord insertion

Periumbilical, right-sided mass

Recognizable loops of bowel outside the abdomen

Intrauterine growth restriction

The evidence of persistent herniation of the bowel, and potentially other abdominal organs, into the base of the umbilical cord leads to the diagnosis of an

omphalocele

what is associated with omphaloceles?

Trisomy 18, trisomy 13, Turner syndrome, and Beckwith–Wiedemann syndrome

. Pentalogy of Cantrell is another group of anomalies that include an

omphalocele, along with ectopic cordis, cleft sternum, anterior diaphragmatic defect, and pericardial defects

Clinical Findings of Omphalocele

Elevated MSAFP

Sonographic Findings of Omphalocele

Midline abdominal mass at the base of the umbilical cord that contains bowel, the liver, and/or other abdominal organs

Abnormal cord insertion into the midline abdominal mass

Multiple associated anomalies