Diagnostic ultrasound ( PDFDrive )

CHAPTER 39 The Fetal Urogenital Tract 1363
hypoperistalsis, and microcolon. Diferentiating this condition
from the more common posterior urethral valves is important
because MMIHS carries a dismal prognosis and fetal bladder
shunting is not indicated. he key distinguishing features are
(1) the amniotic luid is normal or increased; (2) the fetus is
usually female; and (3) very rarely, a dilated small bowel may
be present. 203 MRI is a useful adjunct for diagnosis; it can conirm
the presence of microcolon when an enlarged bladder is visualized
on ultrasound. 204 In fetuses with LUTO, an abnormal amniotic
luid digestive enzyme proile has shown a sensitivity of 80%
and a speciicity of 89% for MMIHS. 205 he precise genetic etiology
of this syndrome remains unclear. Most occurrences are sporadic,
and case reports of familial consanguineous cases have been
described, suggesting an autosomal recessive inheritance
model. 206,207 Recently, genetic advances in whole-exome sequencing
have allowed the identiication of mutations, such as ACTG2,
encoding smooth-muscle actin, which may be implicated in the
etiology of the disease. 208,209
Cloacal malformation is very rare, with an incidence of
1 : 50,000 births. It results from failure of migration and/or fusion
of the urorectal septum with the cloacal membrane. 210 his in
turn causes persistence of the cloaca and cloacal membrane and
failure of normal diferentiation of external genitalia. here is a
wide spectrum of abnormalities, with the most severe being
cloacal dysgenesis (in which there is no perineal opening). In
some cases, there is a single perineal opening that serves as the
outlet for urine, genital secretions, and meconium. Lower UT
abnormalities (relux, ureteral ectopia, duplication of bladder)
and genital abnormalities (duplication or atresia of uterus and
vagina) are common, as are abnormalities of the kidneys and
spine. Additional complications are related to obstruction of
the urinary, genital, and gastrointestinal tracts. he usual
sonographic presentation is that of LUTO in a female fetus (Fig.
39.37, Video 39.10). One or more cystic structures are seen arising
from the pelvis, and their appearance depends on the anatomy
involved. here may be a dilated bladder, with associated bilateral
hydroureter and hydronephrosis. A septate cystic mass may be
seen due to hydrocolpos and associated müllerian duct anomalies.
he distal bowel may be dilated. If there is a communication
between the distal bowel and the urinary system, a cystic mass
containing calciications (meconium mixed with urine) may be
seen 211 (see Fig. 39.37B). Oligohydramnios, and in some cases,
anhydramnios, may be present. Other sonographic indings
include ascites, ambiguous genitalia, and vertebral anomalies. 212
Prenatal sonographic diagnosis of cloacal malformation is challenging.
Fetal MRI is useful for assessment of the anorectal and
pelvic anatomy. It can clarify cloacal malformations with high
position of the distal bowel and a long common cloacal channel. 213
In Utero Intervention: Fetal Vesicoamniotic
Shunting and Cystoscopy
For a carefully selected group of fetuses with severe LUTO,
permanent in utero bladder drainage may be a therapeutic option.
he objective of vesicoamniotic shunting is to allow free drainage
of urine from the bladder into the amniotic cavity. his decompresses
the UT and should correct oligohydramnios, may theoretically
prevent or stabilize renal dysplastic change, and allows
unimpeded lung development. his approach assumes that renal
function has not already been destroyed. Careful selection of
suitable cases is critical, and the goal is oten the identiication
and rigorous evaluation of reliable predictors of postnatal renal
function. 33,214-221
A detailed sonographic evaluation of the fetus is a prerequisite,
to deine the probable cause and evaluate prognosis. Intervention
is not indicated if the ultrasound examination suggests either
MMIHS or cloacal dysgenesis or if the fetus is female, because
of their uniformly dismal prognosis.
Fine-needle aspiration under ultrasound guidance (vesicocentesis)
allows for fetal renal function, karyotype, and microarray
to be evaluated. 33,216-218 If the urine reaccumulates rapidly (which
itself may indicate function) and the other prognostic factors
A
B
FIG. 39.37 Cloacal Dysgenesis. (A) Transverse view of the pelvis in a 17-week fetus shows a large bladder (B) and (B) sagittal view of the
left side of the abdomen shows a cystic mass (arrow) superior to the bladder, representing a dilated bowel loop with intraluminal calciications
(meconium mixed with urine), indicating a urinary-bowel istula. See also Video 39.10.