the fetal stomach is visible from 9 weeks of gestation as a sonolucent cystic
structure in the upper left quadrant of the abdomen. The bowel is normally
uniformly echogenic until the third trimester of pregnancy, when prominent
meconium-filled loops of large bowel are commonly seen. The liver comprises
most of the upper abdomen and the left lobe is greater in size than the right
due to its greater supply of oxygenated blood. The gall bladder is seen as
an ovoid cystic structure to the right and below the intrahepatic portion
of the umbilical vein. The spleen may also be visualized in a transverse plane
posterior and to the left of the fetal stomach. The abdominal circumference
should be measured in a cross-section of the abdomen demonstrating the stomach
and portal sinus of the liver. The visceral situs should be assessed, by demonstrating
the relative position of the stomach, hepatic vessels, abdominal aorta and
inferior vena cava.
atresia and tracheoesophageal fistulae, found in about 90% of cases, result
from failure of the primitive foregut to divide into the anterior trachea
and posterior esophagus, which normally occurs during the 4th week of gestation.
atresia is found in about 1 in 3000 births.
atresia and tracheoesophageal fistulae are sporadic abnormalities. Chromosomal
abnormalities (mainly trisomy 18 or 21) are found in about 20% of fetuses.
Other major defects, mainly cardiac, are found in about 50% of the cases.
Tracheoesophageal fistulae may be seen as part of the VATER association (vertebral
and ventricular septal defects, anal atresia, tracheoesophageal fistula, renal
anomalies, radial dysplasia and single umbilical artery). In over 80% of cases,
esophageal atresia occurs in association with a tracheo-esophageal fistula,
allowing intake of amniotic fluid from the stomach, they may be therefore
normally distended, particularly in early gestation.
the diagnosis of esophageal atresia is suspected when, in the presence of
polyhydramnios (usually after 25 weeks), repeated ultrasonographic examinations
fail to demonstrate the fetal stomach.
a 180K clip of esophageal atresia
gastric secretions may be sufficient to distend the stomach and make it visible.
If there is an associated fistula, the stomach may look normal. Occasionally
(after 25 weeks), the dilated proximal esophageal pouch can be seen as an
elongated upper mediastinal and retrocardiac anechoic structure. This is a
dynamic finding, however, that occurs only at the time of fetal swallowing,
and requires therefore prolonged sonographic visualization.
differential diagnosis for the combination of absent stomach and polyhydramnios
includes intrathoracic compression, by conditions such as diaphragmatic hernia,
and muscular-skeletal anomalies causing inability of the fetus to swallow.
is primarily dependent on gestation at delivery and the presence of other
anomalies. Thus, for babies with an isolated tracheoesophageal fistula, born
after 32 weeks, when an early diagnosis is made, avoiding reflux and aspiration
pneumonitis, postoperative survival is more than 95%.
5 weeks of embryonic life, the lumen of the duodenum is obliterated by proliferating
epithelium. The patency of the lumen is usually restored by the 11th week
and failure of vacuolization may lead to stenosis or atresia. Duodenal obstruction
can also be caused by compression from the surrounding annular pancreas or
by peritoneal fibrous bands.
atresia is found in about 1 per 5000 births.
atresia is a sporadic abnormality, although, in some cases, there is an autosomal
recessive pattern of inheritance. Approximately half of fetuses with duodenal
atresia have associated abnormalities, including trisomy 21 (in about 40%
of fetuses) and skeletal defects (vertebral and rib anomalies, sacral agenesis,
radial abnormalities and talipes), gastrointestinal abnormalities (esophageal
atresia/tracheoesophageal fistula, intestinal malrotation, Meckel’s diverticulum
and anorectal atresia), cardiac and renal defects.
diagnosis is based on the demonstration of the characteristic ‘double bubble’
appearance of the dilated stomach and proximal duodenum, commonly associated
a 200K clip of duodenal atresia
obstruction due to an central web may result in only a ‘single bubble’, representing
the fluid-filled stomach. Continuity of the duodenum with the stomach should
be demonstrated to differentiate a distended duodenum from other cystic masses,
including choledochal or hepatic cysts. Although the characteristic ‘double
bubble’ can be seen as early as 20 weeks, it is usually not diagnosed until
after 25 weeks, suggesting that the fetus is unable to swallow a sufficient
volume of amniotic fluid for bowel dilatation to occur before the end of the
second trimester of pregnancy.
after surgery in cases with isolated duodenal atresia is more than 95%.
obstructions are either intrinsic or extrinsic. Intrinsic lesions result from
absent (atresia) or partial (stenosis) recanalization of the intestine. In
cases of atresia, the two segments of the gut may be either completely separated
or connected by a fibrous cord. In cases of stenosis, the lumen of the gut
is narrowed or the two intestinal segments are separated by a septum with
a central diaphragm. Apple-peel atresia is characterized by absence of a vast
segment of the small bowel, which can include distal duodenum, the entire
jejunum and proximal ileus. Extrinsic obstructions are caused by malrotation
of the colon with volvulus, peritoneal bands, meconium ileus, and agangliosis
(Hirschsprung’s disease). The most frequent site of small bowel obstruction
is distal ileus (35%), followed by proximal jejunum (30%), distal jejunum
(20%), proximal ileus (15%). In about 5% of cases, obstructions occur in multiple
sites. Anorectal atresia results from abnormal division of the cloaca during
the 9th week of development.
obstruction is found in about 1 per 2000 births; in about half of the cases,
there is small bowel obstruction and in the other half anorectal atresia.
the condition is usually sporadic, in multiple intestinal atresia, familial
cases have been described. Associated abnormalities and chromosomal defects
are rare. In contrast with anorectal atresia, associated defects such as genitourinary,
vertebral, cardiovascular and gastrointestinal anomalies are found in about
80% of cases.
lumens of the small bowel and colon do not normally exceed 7 mm and 20 mm,
respectively. Diagnosis of obstruction is usually made quite late in pregnancy
(after 25 weeks), as dilatation of the intestinal lumen is slow and progressive.
Jejunal and ileal obstructions are imaged as multiple fluid-filled loops of
bowel in the abdomen.
The abdomen is
usually distended and active peristalsis may be observed.
bowel perforation occurs, transient ascites, meconium peritonitis and meconium
pseudocysts may ensue.
a 200K clip of meconium peritonitis
(usually after 25 weeks) is common, especially with proximal obstructions.
Bowel enlargement and polyhydramnios may be found in fetuses with Hirschsprung’s
disease, the megacystis–microcolon–intestinal hypoperistalsis syndrome and
congenital chloride diarrhea. When considering a diagnosis of small bowel
obstruction, care should be taken to exclude renal tract abnormalities and
other intra-abdominal cysts such as mesenteric, ovarian or duplication cysts.
In anorectal atresia, prenatal diagnosis is usually difficult because the
proximal bowel may not demonstrate significant dilatation and the amniotic
fluid volume is usually normal; occasionally calcified intraluminal meconium
in the fetal pelvis may be seen.
bowel obstruction typically present in the early neonatal period with symptoms
of vomiting and abdominal distention. The prognosis is related to the gestational
age at delivery, the presence of associated abnormalities and site of obstruction.
In those born after 32 weeks with isolated obstruction requiring resection
of only a short segment of bowel, survival is more than 95%. Loss of large
segments of bowel can lead to short gut syndrome, which is a lethal condition.
disease is characterized by congenital absence of intramural parasympathetic
nerve ganglia in a segment of the colon. It derives from failure of migration
of neuroblasts from the neural crest to the bowel segments, which generally
occurs between the 6th and 12th weeks of gestation. Another theory suggests
that the disease is caused by degeneration of normally migrated neuroblasts
during either pre- or postnatal life.
disease occurs in about 1 in 3000 births.
is considered to be a sporadic disease, although in about 5% of cases there
is a familial inheritance. In a small number of cases, Hirschsprung’s disease
is associated with trisomy 21.
aganglionic segment is unable to transmit a peristaltic wave, and therefore
meconium accumulates and causes dilatation of the lumen of the bowel.
appearance is similar to that of anorectal atresia, when the affected segment
is colon or rectum. Polyhydramnios and dilatation of the loops are present
in the case of small bowel involvement; on this occasion, it is not different
from other types of obstruction.
surgery is aimed at removing the affected segment and this may be a two-stage
procedure with temporary colostomy. Neonatal mortality is approximately 20%.
perforation of the bowel may lead to a local sterile chemical peritonitis,
with the development of a dense calcified mass of fibrous tissue sealing off
the perforation. Bowel perforation usually occurs proximal to some form of
obstruction, although this cannot always be demonstrated.
stenosis or atresia and meconium ileus account for 65% of the cases. Other
causes include volvulus and Meckel’s diverticulum. Meconium ileus is the impaction
of abnormally thick and sticky meconium in the distal ileum, and, in the majority
of cases, this is due to cystic fibrosis.
peritonitis is found in about 1 in 3000 births.
the typical case, meconium peritonitis is featured b y the association of
intra-abdominal echogenic area, dilated bowel loops and ascites.
diagnosis should be considered if the fetal bowel is observed to be dilated
or whenever an area of fetal intra-abdominal hyperechogenicity is detected.
differential diagnosis of hyperechogenic bowel includes: intra-amniotic hemorrhage;
early ascites; fetal hypoxia; meconium peritonitis; and cystic fibrosis.
and hyperechogenic fetal bowel at 16–18 weeks of gestation may be present
in 75% of fetuses with cystic fibrosis. The prevalence of cystic fibrosis
in fetuses with prenatal diagnosis of intestinal obstruction may be about
10%. Therefore, when other causes of bowel hyperechogenicity have been excluded,
DNA studies for cystic fibrosis should be considered.
peritonitis is associated with a more than 50% mortality in the neonatal period.
fetal liver and spleen can be measured by ultrasonography. Causes of hepatosplenomegaly
include immune and non-immune hydrops, congenital infection and metabolic
disorders, and it is seen in Beckwith–Wiedemann and Zellweger syndromes. Hepatic
enlargement may also be caused by hemangioma, which is usually hypoechogenic,
or hepatoblastoma (the most frequent malignant tumor in fetal life), in which
there are areas of calcification.
calcifications are echogenic foci in the parenchyma or the capsule of the
calcifications are found at mid-trimester ultrasonography in about 1 per 2000
vast majority of cases are idiopathic but, in a few cases, hepatic calcifications
have been found in association with congenital infections and chromosomal
or multiple echogenic foci (1–2 mm in diameter) are observed within the substance
of the liver or in the capsule.
depends on the presence of associated infection or chromosomal defects. Isolated
foci are of no pathological significance.
cystic masses are frequent findings at ultrasound examination. Renal tract
anomalies or dilated bowel are the most common explanations, although cystic
structures may arise from the biliary tree, ovaries, mesentery or uterus.
The correct diagnosis of these abnormalities may not be possible by ultrasound
examination, but the most likely diagnosis is usually suggested by the position
of the cyst, its relationship with other structures and the normality of other
cysts represent cystic dilatation of the common biliary duct. They are uncommon
and their etiology is unknown. Prenatally, the diagnosis may be made ultrasonographically
by the demonstration of a cyst in the upper right side of the fetal abdomen.
The differential diagnosis includes enteric duplication cyst, liver cysts,
situs inversus or duodenal atresia. The absence of polyhydramnios or peristalsis
may help to differentiate the condition from bowel disorders. Postnatally,
early diagnosis and removal of the cyst may avoid the development of biliary
cirrhosis, portal hypertension, calculi formation or adenocarcinoma. The operative
mortality is about 10%.
cysts are common and they may be found in up to one-third of newborns at autopsy,
although they are usually small and asymptomatic. Fetal ovarian cysts are
hormone-sensitive (human chorionic gonadotropin from the placenta) and tend
to occur after 25 weeks of gestation; they more common in diabetic or rhesus
isoimmunized mothers as a result of placental hyperplasia. The majority of
cysts are benign and resolve spontaneously in the neonatal period. Potential
complications include development of ascites, torsion, infarction or rupture.
Prenatally, the cysts are usually unilateral and unilocular, although, if
the cyst undergoes torsion or hemorrhage, the appearance is complex or solid.
Large ovarian cysts can be found in association with polyhydramnios, possibly
as a consequence of compression of the bowel. Obstetric management should
not be changed, unless an enormous or rapidly enlarging cyst is detected or
there is associated polyhydramnios; in these cases, prenatal aspiration may
be considered. A difficult differential diagnosis is from hydrometrocolpos,
which also presents as a cystic or solid mass arising from the pelvis of a
female fetus. Other genitourinary or gastrointestinal anomalies are common
and include renal agenesis, polycystic kidneys, esophageal atresia, duodenal
atresia and imperforate anus. Most cases are sporadic, although a few cases
are genetic, such as the autosomal recessive McKusick–Kaufman syndrome with
hydrometrocolpos, polydactyly and congenital heart disease.
or omental cysts
or omental cysts may represent obstructed lymphatic drainage or lymphatic
hamartomas. The fluid contents may be serous, chylous or hemorrhagic. Antenatally,
the diagnosis is suggested by the finding of a multiseptate or unilocular,
usually mid-line, cystic lesion of variable size; a solid appearance may be
secondary to hemorrhage. Antenatal aspiration may be considered in cases of
massive cysts resulting in thoracic compression. Postnatal management is conservative
and surgery is reserved for cases with symptoms of bowel obstruction or acute
abdominal pain following torsion or hemorrhage into a cyst. Complete excision
of cysts may not be possible because of the proximity of major blood vessels
and in up to 20% of cases there is recurrence after surgery. Although malignant
change in mesenteric cysts has been described, this is rare.
cysts are typically located in the right lobe of the liver. They are quite
rare and result from obstruction of the hepatic biliary system. They appear
as unilocular, intrahepatic cysts, and they are usually asymptomatic, although
rarely may show complications such as infections or hemorrhages. In 30% of
the cases of polycystic kidneys (adult type), asymptomatic hepatic cysts may
are quite rare, and may be located along the entire gastrointestinal tract.
They sonographically appear as tubular or cystic structures of variable size.
They may be isolated or associated with other gastrointestinal malformations. Differential
diagnosis includes other intra-abdominal cystic structures and also bronchogenic
cysts, adenomatoid cystic malformation of the lung and pulmonary sequestration.
Thickness of the muscular wall of the cysts and presence of peristalsis may
facilitate the diagnosis. Postnatally, surgical removal is carried out.
of the umbilical vein
of the umbilical vein, which are very rare, can be divided in three groups:
(1) Persistence of the right umbilical vein
with ductus venosus and presence or absence of left umbical vein;
(2) Absence of the ductus venosus with extrahepatic
insertion of the umbilical vein; and
(3) Dilated umbilical vein with normal insertion.
the umbilical vein enters the abdomen almost centrally at the level of the
liver and courses on the left of the gallbladder. Persistence of the right
umbilical vein is demonstrated by the fact that it is localized on the right
of the gallbladder, bending towards the stomach. Color Doppler may help to
diagnose these anomalies and may allow the differential diagnosis with other
cystic abdominal lesions. Associated anomalies are frequent in anomalies of
the first two groups and this influences the prognosis. These anomalies include
cardiac, skeletal, gastrointestinal and urinary anomalies. The anomalies of
the third group are rarely associated with other anomalies, and prognosis
depends on the time at diagnosis and dimension of the varicosity.
© 2000 by Pilu, Nicolaides, Ximenes & Jeanty