Diagnostic ultrasound ( PDFDrive )

1316 PART IV Obstetric and Fetal Sonography
echogenic bowel is unclear, but it has been attributed to the
presence of GI dysfunction and dysmotility. 113 Intestinal stasis,
for any reason, can lead to increased absorption of luid from
the bowel lumen, which can result in thick meconium and
therefore increased echogenicity of the bowel content. 114 Other
chromosomal abnormalities that have been associated with
echogenic bowel include trisomies 13 and 18, 45,X0, and
triploidies. 110,111,115
Cystic Fibrosis. Echogenic bowel, meconium ileus, and
meconium peritonitis are possible sonographic indings in fetuses
with cystic ibrosis. 116 he echogenic appearance of the bowel
in fetuses with cystic ibrosis is the result of the biochemical
alterations in the secretory-digestive-absorptive function of the
small intestinal mucosa, which can result in the meconium being
more viscous than normal and therefore more echogenic. 117 he
incidence of cystic ibrosis in fetuses with isolated echogenic
bowel varies from 1.3% to 5%. 106,118,119
Intraamniotic Bleeding. Echogenic bowel has been noted
in pregnancies complicated by vaginal bleeding, in those with
asymptomatic subchorionic hemorrhage, and following invasive
procedures such as chorionic villous sampling and amniocentesis.
Each of these conditions may result in intraamniotic bleeding,
and the blood-containing amniotic luid swallowed by the fetus
can be visible as echogenic debris in the fetal stomach or as
increased echogenicity of the bowel content (Fig. 38.16C). 114,120
In a case series of pregnant women undergoing amniocentesis,
there was evidence of blood in the amniotic luid on spectrophotometry
of 8 in 40 (20%) of those with echogenic bowel
compared to 3 in 64 (5%) of those without. 121 In one series, 19%
of fetuses with isolated echogenic bowel had sonographic evidence
of intrauterine bleeding, of which 70% were conirmed to have
intraamniotic bleeding on amniocentesis. 122 History of bleeding
during pregnancy, history of invasive procedure earlier in
pregnancy, sonographic evidence of retroplacental or subchorionic
hemorrhage, or evidence of debris in the fetal stomach provides
support for intraamniotic bleeding as the cause of echogenic
bowel.
Fetal Infection. Echogenic bowel is one of the manifestations
of fetal infection, including cytomegalovirus (CMV), parvovirus
B19, varicella, herpes simplex, and toxoplasmosis (Fig. 38.16B). 123
he incidence of infection in fetuses with echogenic bowel is in
the range of 0.5% to 6.3%. 122,124,125 he cause of the echogenic
bowel in fetuses with infection is not known but may be related
to inlammation and edema of the bowel wall as well as the
associated decreased peristalsis of the infected bowel.
Bowel Obstruction. As previously noted, bowel of obstruction
or stasis for any reason, including GI atresia or Hirschsprung
disease, 89 can result in thickening of the meconium and therefore
increase in the echogenicity of bowel content.
Fetal Growth Restriction and Fetal Demise. he risk of
both fetal growth restriction and fetal demise increases in the
second and third trimesters in fetuses with echogenic bowel.
he reported incidence is 10% to 20% for fetal growth restriction
102,118 and 6% to 15% for fetal demise. 73,118,126 In a recent study
of 188 fetuses with isolated echogenic bowel (i.e., ater the exclusion
of chromosomal abnormalities, major malformation, and
fetal infection), the rate of fetal growth restriction and fetal demise
were 19.5% and 7.3%, respectively (compared with 12.9% and
0.9% in the control group, respectively). Possible explanation
for these indings is the association between subchorionic bleeding
(which can result in echogenic bowel) with fetal growth restriction
and fetal demise. 127 In addition, in cases of severe fetal growth
restriction, it is believed that redistribution of cardiac output in
the compromised fetus to vital organs (i.e., brain, heart, and
adrenal gland) results in decreased splanchnic blood low, including
perfusion to the bowel, which can result in impaired peristalsis.
128 he association of echogenic bowel with fetal anemia,
which can also result in bowel hypoxia, provides support to this
hypothesis. 129
Summary. Given the associations described previously, the
inding of echogenic bowel requires careful investigation and
appropriate monitoring. he evaluation of pregnancies with
echogenic bowel typically includes (1) genetic counseling and
consideration of amniocentesis or cell-free fetal DNA testing;
(2) parental screening for cystic ibrosis; (3) maternal serology
for viral infections, including CMV and parvovirus B19; (4)
detailed sonographic assessment for associated structural
anomalies or sot markers, signs of bowel obstruction, assessment
of fetal biometry, placental morphology, and amniotic luid; and
(5) follow-up for growth. Information regarding episodes of
vaginal bleeding or invasive testing earlier in pregnancy should
be recorded. In cases where the investigation is negative, the
inding of “isolated” echogenic bowel may represent a normal
variant or a false-positive inding, and fetal outcome may be
normal.
Liver
he fetal liver is clearly visualized in the upper abdomen in the
second half of gestation, although earlier in gestation it has an
echogenicity similar to renal echoes.
Hepatomegaly
Given the asymmetrical shape of the liver, accurate determination
of its size is diicult and is associated with high interobserver
variability. herefore in many cases the diagnosis of hepatomegaly
is made subjectively. Hepatomegaly is associated with a variety
of conditions including fetal hemolytic anemia which results
in a compensatory increase in hematopoiesis within the liver, 130
metabolic and storage diseases, fetal infections 131 (Fig. 38.17),
liver masses, hepatic congestion secondary to cardiac failure,
and overgrowth syndromes such as Beckwith-Wiedemann
syndrome. 132,133 Hepatomegaly has also been associated with
trisomy 21, possibly because of the abnormal myelopoiesis in
these fetuses. 134
Hepatic Calciications
Hepatic calciications can be single or multiple (Fig. 38.18). In
one series, hepatic calciications were identiied in 14 of 24,600
consecutive pregnancies scanned between 15 and 26 weeks,
representing an incidence of 1 in 1750 pregnancies. 135 he
pathophysiology of hepatic calciications in otherwise normal
fetuses is unknown, and in the majority of cases, such calciications
represent an isolated inding and have no clinical consequence.
136 However, hepatic calciications are associated with