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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_32_библиотеки_им_акад_М_И_Перельмана
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Prenatal Diagnosis
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SARAH L HECHT and VIJAYA M VEMULAKONDA
Topics covered
4
Prenatal imaging
Hydronephrotic anomalies
Classication
Diagnoses
INTRODUCTION
Since its inception in the 1970s, prenatal screening with fetal ultrasonography has become nearly
ubiquitous. Abnormalities of the urogenital system are among the most commonly prenatally
detected congenital anomalies because of their
relatively high incidence and the fact that dilatation of the fetal urinary tract (hydronephrosis) is
readily detected on ultrasound. e overwhelming majority of prenatally detected urologic
abnormalities are associated with some degree of
hydronephrosis. In most cases, prenatally detected
hydronephrosis is a mild and/or transient ultrasound nding. While most infants with prenatally
detected hydronephrosis have a very favorable outcome, a small but signicant minority will prove
to have signicant renal disease. Depending on
prevailing attitudes to termination of pregnancy
a small proportion may survive to term but then
die shortly aer birth. Researchers and consensus
panels have invested substantial eort into trying
Initial management
Non-hydronephrotic anomalies
Fetal intervention
Counseling
to distinguish between those ultrasound ndings which denote clinically signicant urologic
disease and ultrasound appearances which are
essentially innocent ndings of little or no clinical
signicance. Many studies have been undertaken
with the aim of dening reliable criteria to guide
the postnatal investigation and management of
infants with prenatally detected hydronephrosis.
However, this remains a source of controversy.
PRENATAL IMAGING
Ultrasonography
Ultrasonography is the primary imaging modality during pregnancy. First trimester ultrasound
is frequently obtained to conrm a viable intrauterine pregnancy, estimate conception date, and
assess nuchal pad translucency to screen for aneuploidy. However, this is of limited value in screening
for most congenital anomalies. e World Health
43
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Organization recommends a single ultrasound
prior to 24 weeks gestation. In the United States,
the primary anatomic survey is obtained at 18–22
weeks gestational age, with additional scans being
performed in high risk pregnancies or if a congenital anomaly is suspected. e second trimester scan
usual ly provides sucient anatomica l detail to screen
for major congenital anomalies. Additional information includes the position, size and movement of
the fetus, heart rate, placental position, and the volume of amniotic uid. e sensitivity and specicity
of prenatal ultrasonography for the detection of congenital anomalies depends on many factors including maternal obesity, fetal position, sonographic
equipment, and experience of the person performing the scan. Most of the serious, potentially lethal
genitourinary anomalies, such as posterior urethral
valves and bilateral renal agenesis are detected in the
second trimester. However more common anomalies such as vesicoureteral reux, ectopic ureters, and
ureteroceles are not reliably detected at this stage in
gestation and may not be detected prenatally unless
further scans are performed later in pregnancy.
Magnetic Resonance Imaging
During the last two decades, prenatal magnetic
resonance imaging (MRI) has been gaining popularity as a means of providing more detailed
information on fetal abnormalities detected by
prenatal ultrasound. MRI has higher so tissue
contrast resolution and is not limited by maternal
habitus, fetal position, ossied structures or oligohydramnios. MRI does not use ionizing radiation
and poses no known risk to the fetus. Common
applications in urological diagnosis include distinguishing hydronephrosis from cystic abnormalities, delineating ureteral anatomy including
duplication, ectopia, and ureteroceles, and clarifying the anatomy of complex anomalies such as cloacal anomalies and exstrophy-epispadias complex.
e reported incidence of fetal hydronephrosis
ranges from 0.5% to 5% but this gure varies
according to the gestational age at which scans
are performed. Mild prenatally detected hydronephrosis is usually an innocent ultrasound nding which represents a transient physiologic state
of no clinical signicance. e overall incidence
of antenatally detected hydronephrosis associated with a clinically signicant uropathy is
approximately 0.2%. It is important to minimize
unnecessary investigation and repeated scans so
as not to exacerbate parental anxiety. ere is a
broad correlation between the degree of hydronephrosis and the probable severity of the abnormality aecting the kidneys and/or urinary tract.
Several classication systems have been developed to grade the severity of fetal hydronephrosis
and guide further investigation but there is no
consensus on which is the best for this purpose.
Classication Systems
Anterior-posterior renal
pelvic diameter
is system classies the severity of hydronephrosis based solely on the degree of dilatation of
the renal pelvis. It is based on measurements of
the anterior-posterior (AP) diameter of the renal
pelvis in the transverse plane at the level of the
renal hilum (within the connes of the parenchyma). e AP renal pelvic diameter varies
according to gestational age. erefore, the value
chosen as the upper limit of normality strongly
inuences the specicity and sensitivity of AP
diameter as a predictor of genitourinary pathology at dierent stages in pregnancy. Although
there is no universal consensus, a renal pelvic
diameter of greater than 10 mm in the second
trimester is generally regarded as a signicant
nding, with an AP diameter of greater than
15mm being regarded as the upper threshold in
the third trimester.
HYDRONEPHROSIS
Dilatation of the fetal urinary tract (fetal hydronephrosis) is the most common genitourinary
abnormality identied on antenatal screening.
Society for Fetal Urology (SFU)
classication
e SFU developed a grading system for neonatal
and infant hydronephrosis based on a combination
Hydronephrosis / Classication Systems 45
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of dilatation of the renal pelvis, calyceal dilatation
and a subjective assessment of parenchymal thickness. ough originally devised for grading hydronephrosis postnatally, the SFU classication is also
commonly applied to antenatal hydronephrosis.
e SFU grading is based on the following criteria:
Grade 0: Normal ultrasound ndings with no
dilatation
Grade I: Dilatation conned to the renal pelvis
Grade II: Dilatation of the renal pelvis accompa-
nied by dilatation of the major calyces
Grade III: Dilatation of the renal pelvis accom-
panied by dilatation of the major and minor
calyces
Grade IV: As for Grade III plus thinning of the
renal cortex (Figure 4.1)
Urinary Tract Dilation (UTD)
classication
e UTD classication was devised by a multidisciplinary consensus panel with the aims of
unifying dierent grading systems, introducing consistency into the terminology applied to
antenatal and postnatal classication of hydronephrosis and correlating the antenatal grading
with the clinical signicance of the underlying
genitourinary abnormality. e classication
encompasses the following ultrasound ndings:
1. Anterior-posterior renal pelvic diameter
2. Calyceal dilation
3. Renal parenchymal thickness
4. Renal parenchymal appearance (echo-
genicity, corticomedullary dierentiation,
cortical cysts)
5. Ureteral dilation
6. Bladder pathology (ureterocele, wall thicken-
ing, dilated posterior urethra)
7. Oligohydramnios (antenatal classication
only)
is is the only classication to take account
of ureteral and lower urinary tract abnormalities and the only one to oer clinical guidance
according to risk. Patients are allocated to different risk categories by a combination of ultrasound ndings (with the most severe ndings
taking precedence) and gestational or postnatal
age. Antenatal and postnatal risk categories are
denoted by A or P, respectively. ere are two
antenatal risk categories: A1 (low risk) and A2-3
(intermediate/high risk) and three postnatal risk
categories: P1 (low risk), P2 (intermediate risk),
and P3 (high risk). (Figure 4.2)
Each risk category has associated clinical recommendations to guide the clinician
(Figure 4.3). e physiological reduction in urine
output which normally occurs during the rst
48 hours aer birth may reduce the sensitivity
of ultrasound for the detection of hydronephrosis during this period. Decision-making should
therefore be based on ultrasound ndings aer
48 hours.
Figure 4.1 (a) Unilateral SFU grade 4 hydronephrosis with blunted calyces and thinned, echogenic
renal cortex at 22/40 weeks. (b) Bilateral SFU grade 4 hydronephrosis at 22/40 weeks.
46 Prenatal Diagnosis
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Figure 4.2 UTD risk-based sonographic classication of hydronephrosis. (A) Prenatal classication.
Central and peripheral calyceal dilation may be difcult to evaluate early in gestation. Oligohydramnios
must be suspected to result from a genitourinary cause. (B) Postnatal sonographic classication of
hydronephrosis.
Postnatal investigation
Prenatally detected hydronephrosis is a nonspecic nding and, where appropriate, further
imaging investigations are required to establish
the urological diagnosis. Postnatal diagnostic
imaging always begins with a renal and bladder
ultrasound. Depending on the initial ultrasound
ndings and other factors, further investigations
typically comprise a voiding cystourethrogram
(VCUG) and functional isotope renography.
Mild hydronephrosis
Dilatation of the renal pelvis corresponding to
Grade I on the SFU scale is a common nding
which is present in 1:100 pregnancies. It is oen
a self-limiting physiological phenomenon –
which resolves spontaneously by the third trimester in more than 50% of cases. ere is now
general agreement that this nding can usually
be disregarded if the dilatation is conned to
the renal pelvis and the AP diameter is less than
10mm. Follow up studies of children born with
mild hydronephrosis have found that their incidence of UTIs and bladder symptoms in childhood is no higher than in age matched normal
controls. Nevertheless, the discovery of mild
hydronephrosis on routine antenatal ultrasonography can cause considerable parental anxiety and it is important that parents are given
appropriate reassurance. It is also important
that newborn infants with mild hydronephrosis are not submitted to unnecessary, invasive
investigations. Mild hydronephrosis may be a
marker of underlying VUR but when this is the
case it usually low grade and of doubtful clinical signicance. SFU and AUA guidelines do not
advocate routine VCUG in infants with mild
(SFU Grade I) prenatally detected hydronephrosis but recommend that VCUG is used more
selectively on the basis of additional ultrasonographic criteria.
Ureteropelvic junction (UPJ)
obstruction
e most common underlying cause of clinically signicant hydronephrosis is UPJ obstruction, which occurs in approximately 1 in 500 live
births. UPJ obstruction is characterized by partial
or intermittent occlusion of the lumen of the UPJ.
Dilatation is conned to the renal collecting systems unless the UPJ obstruction is associated w ith
other urinary tract abnormalities – in which case
ureteral dilatation and/or bladder abnormalities
Hydronephrosis / Classication Systems 47
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Figure 4.3 UTD risk-based guidelines for management of hydronephrosis. (A) Follow-up
recommendations for prenatally diagnosed hydronephrosis. (B) Management recommendations
based on postnatal ultrasound.
may also be present. Boys are aected more commonly than girls, and approximately 10% of cases
are bilateral. ere is usually a good correlation between the degree of hydronephrosis and
the severity of obstruction and impact on renal
function (as demonstrated by isotope renography). e indications for pyeloplasty and the
arguments surrounding conservative or surgical
management of prenatally detected UPJ obstruction are reviewed in greater detail in Chapter 7.
In brief, it is generally agreed that early pyeloplasty is indicated for infants with severe hydronephrosis and/or reduced dierential function.
Pyeloplasty remains the surgical “gold standard”
and has a very high success rate for the correction
of UPJ obstruction.
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Vesicoureteral reux
As noted already, VUR is one of the conditions
which may give rise to prenatal hydronephrosis.
However, there are no pathognomonic ultrasonographic features and the diagnosis of VUR can
only be reliably established on a postnatal VCUG.
At one time this was performed routinely in all
infants with prenatally detected hydronephrosis,
regardless of severity. However, current SFU and
AUA guidelines recommend that VCUG should
be limited to infants with higher grades of hydronephrosis (III–IV on the SFU scale) and/or those
with ureteral dilatation (hydroureter) or bladder
abnormalities. is is considered in more detail
in Chapter 6.
Other urological conditions
Primary megaureter accounts for around 5–10%
of cases of fetal hydronephrosis. On ultrasound,
the degree of ureteral dilatation may be disproportionally greater than the degree of renal dilatation. Aer 30 weeks gestation a ureteral diameter
of greater than 7 mm is regarded as an abnormal
nding constituting a diagnosis of megaureter.
e postnatal investigation, classication, and
management of megaureters are considered in
Chapter 7. Ureteroceles may be detected pre-
natally and are characterized by appearances
of a thin septum or thin walled cystic structure
within the bladder. is nding may be accompanied by upper tract dilatation and bilateral
hydronephrosis if the ureterocele has prolapsed
into bladder outlet or urethra to cause outow
obstruction. Similarly, ureteroceles which are
associated with an ectopic ureter associated
with the upper pole of a duplex kidney may be
accompanied by ureteral dilatation and abnormal
ultrasound appearances of the kidney itself. e
postnatal assessment and management of ureteroceles and upper tract duplication is addressed
in Chapter 8.
Figure 4.4 Prenatal ultrasound showing a
distended bladder and dilated posterior
urethra (arrow) in a fetus with posterior
urethral valves.
ultrasound ndings such as a distended, thick
walled bladder and dilated posterior urethra
(keyhole sign) (Figure 4.4). Other ultrasound
ndings may include changes in the renal parenchyma denoting dysplasia, bladder diverticula,
patent urachus, or rupture of a renal fornix or
calyx with a perinephric urinoma or urinary
ascites. Oligohydramnios and pulmonary hypoplasia are indicative of severe renal dysplasia and
predictors of a poor prognosis. e role of fetal
intervention is described later in this chapter and
the postnatal investigation and management of
PUV is reviewed in Chapter 9.
Postnatal Management: General
Considerations
e UTD guidelines leave much to the discretion
of the clinician. ere is signicant variation in
the empirical use of prophylactic antibiotics and
indications for VCUG and isotope renography.
Prophylactic antibiotics
Posterior urethral valves (PUV)
Bilateral hydronephrosis in a male fetus is highly
suggestive of posterior urethral valves and the
diagnosis is strongly supported by additional
e published evidence provides limited support
for the use of antibiotic prophylaxis in infants
born with prenatally detected hydronephrosis.
A randomized controlled trial comparing trimethoprim to placebo in infants with prenatally
Non-hydronephrotic anomalies 49
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detected SFU Grade III–IV hydronephrosis is
ongoing. e antibiotics used most commonly for
urinary prophylaxis in neonates include amoxicillin (10–20 mg/kg/day), cephalexin (10 mg/kg/day),
and trimethoprim (2 mg/kg/day). Trimethoprimsulfamethoxazole and nitrofurantoin are contraindicated because of the risks of kernicterus and
hemolytic anemia, respectively. e following prenatally detected urological conditions are generally regarded as indications for postnatal antibiotic
prophylaxis:
●
Lower urinary tract obstruction (e.g. posterior urethral valves, urethral atresia)
●
Ureterovesical junction obstruction (e.g.
obstructing megaureter, ectopic ureter, or
ureterocele)
●
Moderate to high grades of vesicoureteral
reux in girls
Voiding cystourethrogram (VCUG)
e generally accepted indications for postnatal
VCUG include:
●
Abnormal bladder (e.g. thick wall, keyhole
sign, diverticula)
●
Bilateral hydronephrosis in boys (a VCUG
should always be performed prior to discharge from the hospital to investigate for
posterior urethral valves)
●
Multicystic dysplastic kidney with an abnormal contralateral kidney
●
Ureteral dilation
●
Duplex kidney with hydronephrosis in either
moiety
●
Large ureterocele (to investigate possible
prolapse)
Renography
e most widely used radionuclide scan is the
technetium-99 m-mercaptoacetyltriglycine (MAG-3)
diuretic renogram. is has the advantage of combining information on drainage with an assessment of dierential renal function. e technical
aspects are detailed in Chapter 3. Radionuclide
scans are less reliable and the results are more
dicult to interpret in neonates because of the
functional immaturity of their kidneys. For this
reason radionuclide scans should be deferred until
6–8 weeks. of age. e indications for diuretic
renography include:
●
Moderate to severe hydronephrosis (anterior-
posterior renal pelvic diameter >10mm, SFU
Grade III–IV) with absence of vesicoureteral
reux
●
Establishing baseline function prior to sur-
gery to relieve obstruction (e.g. UPJ obstruc-
tion, UVJ obstruction)
●
Conrming poor function in a kidney prior
to nephrectomy
NON-HYDRONEPHROTIC
ANOMALIES
Urological abnormalities which are associated
with hydronephrosis are more readily detected
on prenatal ultrasonography than those which
are not. Nevertheless, other urologic abnormalities can be identied by prenatal ultrasound – and genital anomalies are occasionally
diagnosed prenatally. e nding of a urological anomaly may also lead to the diagnosis of a
more severe, complex congenital abnormality,
or syndrome.
e anatomical features and clinical aspects
of abnormalities of ascent and fusion are
described in Chapter 14. Renal ectopia is frequently associated with other congenital anomalies and may be a component of more complex
syndromes such as VACTERL and agenesis of
the corpus callosum.
A simple ectopic kidney may be located anywhere along the embryological path of ascent
to the lumbar renal fossa. Pelvic kidneys are
the most common form of simple ectopiaaccounting for 60% of all cases. In addition to its
abnormal location, a pelvic kidney is frequently
malrotated, hypoplastic, and irregular in shape.
A horseshoe kidney is formed by fusion of
the le and right kidneys which, in the majority of cases are joined at their lower poles by an
isthmus of renal parenchyma or dysplastic or
50 Prenatal Diagnosis
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brous tissue. Horseshoe kidneys are commonly
found in association with other abnormalities
or syndromes, notably Turner’s syndrome and
abnormalities of the central nervous system, the
gastrointestinal tract, and the skeletal and cardiovascular systems. Crossed renal ectopia is a
rare form of renal ectopia in which both kidneys
are located on the same side of midline. In most
cases the kidneys are fused but the kidney which
is abnormally located retains its vessels and ureters from the contralateral side. e abnormality may either be visualized directly by prenatal
ultrasonography or may be identied indirectly
when a kidney cannot be visualized in the contralateral renal fossa. Further investigation is
usually indicated aer birth because of the relatively high incidence of VUR and other abnormalities. Unilateral renal agenesis occurs in 1 in
around 1300 pregnancies and is more common
in twins. On ultrasound, the lumbar fossa is
empty and the adrenal gland appears elongated.
e contralateral kidney may demonstrate compensatory hypertrophy. Unilateral renal agenesis
is typically a sporadic anomaly but can occur in
association with chromosomal or developmental defects such as DiGeorge syndrome or the
VACTERL complex. It may also occur in conjunction with genital anomalies, notably absence
of the vas deferens in males and Müllerian anomalies in girls. Bilateral renal agenesis occurs in
around 1 in 4000 pregnancies. Ultrasound features comprise absence of both kidneys (empty
lumbar fossae) early anhydramnios, and lack of
bladder lling. If the pregnancy proceeds to term,
bilateral renal agenesis generally results in the
early demise of the infant from pulmonary insufciency and renal failure.
Cystic renal disease is reviewed in detail in
Chapter 10. e form most commonly detected by
prenatal ultrasonography is autosomal recessive
polycystic kidney disease (ARPKD) which occurs
in 1 in 20,000 live births. On ultrasound, the
kidneys typically appear markedly enlarged and
echogenic with poor or even reversed corticomedullary dierentiation (Figure 4.5). However, the
kidneys may appear normal up to the 20th week
of gestation.
Unilateral multicystic dysplastic kidney
(MCDK) is one of the commonest prenatally
detected renal malformations (Figure 4.6). is
partly because of its relative frequency (between
1:2500 and 1:4000 pregnancies) and partly
Figure 4.5 Prenatal imaging at 33/40 weeks showed markedly enlarged, bright kidneys consistent
with infantile ARPKD. (A) Ultrasound shows echogenic kidneys. (B) MRI shows T2 hyperintense
kidneys. The fetal bladder is empty, and there is severe oligohydramnios.
Non-hydronephrotic anomalies / Syndromes, Genital Anomalies 51
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Fetal intervention
Fetal diagnosis prompts the question of fetal intervention. Of the currently available fetal interventions, decompression of an obstructed fetal urinary
tract and intrauterine closure of myelomeningocele
are those of greatest relevance to pediatric urology.
To date, the outcomes of both forms of intervention have been disappointing, with a signicant
incidence of perinatal complications and little evidence of benet for bladder and renal function.
Vesicoamniotic shunting
Figure 4.6 Multicystic dysplastic kidney at
22/40 weeks.
because of the ease with which the uid-lled
cysts can be visualized on ultrasound. Bilateral
MCDK has an incidence of around 1:20,000 and
is a lethal condition. e further investigation of
MCDKs and the controversies surrounding their
management are considered in Chapter 10.
Syndromes, Genital Anomalies
Many conditions involving the genitourinary
system are routinely diagnosed prenatally.
Among the commonest are myelomeningocele
and sacral agenesis – which almost invariably
give rise to neurogenic bladder dysfunction.
Cloacal anomalies may be suspected in fetuses
with a pelvic cystic structure (hydrocolpos),
poorly visualized bladder, and bilateral hydronephrosis. Although bladder exstrophy is associated with a number of diagnostic features these
are not always easy to detect with the result that
only 50% of cases are diagnosed prenatally. Bowel
distension may suggest an anorectal malformation, particularly if this is accompanied by other
features of VACTERL (vertebral, anorectal, cardiac, esophageal stula, renal, limb) anomalies.
Isolated genital anomalies can also be detected
prenatally – the most common being virilized
genitalia in a female with 46 XX DSD due to congenital adrenal hyperplasia. Other forms of DSD
may be identied because of discordance between
genotype and prenatal ultrasonography.
e aims of this form of prenatal intervention for
bladder outlet obstruction are:
1. To prevent pulmonary hypoplasia (the main
cause of neonatal death)
2. To improve the outcome for renal function
3. To improve the outlook for bladder function
e commonest indicat ion is to alleviate t he eects
of outow obstruction due to posterior urethral
valves. Although, fetal cystoscopic valve ablation
and open vesicostomy have been reported the
most commonly performed procedure consists
of decompressing the obstructed urinary tract by
use of a vesicoamniotic shunt. Under ultrasound
guidance a trocar is inserted through the maternal abdominal wall and uterus into the bladder. A
double-pigtail shunt is then introduced, with one
end in the fetal bladder and the other in the amniotic cavity. If there is oligohydramnios it may be
necessary to infuse uid into the amniotic cavity
to facilitate this maneuver (Figure 4.7).
Vesicoamniotic shunting is usually performed
before 26 weeks. When performed aer 26 weeks
it is unlikely to lead to any improvement in
pulmonary function. e selection criteria are
quite complex and include; recent onset of oligohydramnios, functioning kidneys capable of
urine output, normal karyotype and absence of
co-existing congenital abnormalities. Serial fetal
urine sampling is recommended to aid selection
for intervention. High urinary levels of sodium,
calcium, and β2-microglobulin are predictors of
poor renal function (Table 4 .1). e combination
of unfavorable fetal urine electrolyte markers
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