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Chapter 39 ■ The Fetal Urogenital Tract 1357
AMNIOTIC FLUID ASSESSMENT*
Vertical Depth
<2 cm
2-8 cm Normal
>
8 cm
*Largest single pocket method.
Oligohydramnios
Polyhydramnios
marked crowding of fetal parts, and poor definition of
fetal interfaces. The following classification has been proposed for the largest single pocket method: vertical depth
of the pocket less than 2 cm indicates moderate to severe
oligohydramnios, 2 to 8 cm is normal, and greater than
8 cm indicates polyhydramnios.
13
The AFI is obtained by measuring the vertical depth
(mm) of the largest cord-free amniotic fluid pocket in
the four quadrants of the uterus, and the sum of the four
measurements is the index.
14,15
AFI varies with gestational age (Table 39-2). Oligohydramnios should be
defined as more than two standard deviations (2 SD)
below the mean for the specific gestational age, although
the 5th centile value is recommended for screening. The
AFI is a reproducible, objective method for amniotic
fluid measurement.
15
It is useful for following AFV on
serial examinations, particularly by multiple examiners
of varying experience.
However, the semiquantitative methods have several
technical and interpretative limitations.
16
If the fetus is
active, fetal movement may rapidly change the size of
pockets. A large pocket may be replaced by multiple
small pockets between extremities. Measuring pockets
filled with cord, or pockets with large vertical dimensions
but small widths (<
1 cm), leads to overestimation. It is
recommended that when AFI is less than 10 cm, three
measurements should be averaged.15 The AFI is not a
substitute for experience in assessment of AFV. A metaanalysis comparing the use of AFI versus the single
deepest vertical pocket method as predictors of poor
perinatal outcome failed to show an advantage of one
method over the other.
17
URINARY TRACT ABNORMALITIES
The prevalence of urinary tract malformations varies
among studies, likely because of differences in study
population and methods of surveillance. In a recent
analysis of 709,030 births in 12 European countries, the
prevalence of congenital malformations of the urinary
tract was 1.6 per 1000 births.
detection rate was high: 82% and 88.5% in two
1,18
studies.
different centers.
However, it varied from 36% to 100% in
18
Many factors could account for the
variation of prenatal detection rates, including the study
18
The overall prenatal
TABLE 39-2. AMNIOTIC FLUID INDEX
(AFI) VALUES IN NORMAL PREGNANCY
AFI (MM)
WEEK 2.5th 5th 50th 95th 97.5th
16 73 79 121 185 201
17 77 83 127 194 211
18 80 87 133 202 220
19 83 90 137 207 225
20 86 93 141 212 230
21 88 95 143 214 233
22 89 97 145 216 235
23 90 98 146 218 237
24 90 98 147 219 238
25 89 97 147 221 240
26 89 97 147 223 242
27 85 95 146 226 245
28 86 94 146 228 249
29 84 92 145 231 254
30 82 90 145 234 258
31 79 88 144 238 263
32 77 86 144 242 269
33 74 83 143 245 274
34 72 81 142 248 278
35 70 79 140 249 279
36 68 77 138 249 279
37 66 75 135 244 275
38
39 64 72 127 226 255
40 63 71 123 214 240
41 63 70 116 194 216
42 63 69 110 175 192
From Moore TR, Cayle JE. The amniotic fluid index in normal human
pregnancy. Am J Obstet Gynecol 1990;162:1168-1173.
65 73 132 239 269
PRENATAL DIAGNOSIS OF URINARY
TRACT ABNORMALITIES
Assessment of amniotic fluid volume
Localization and characterization of urinary tract
abnormalities
Search for associated abnormalities
population (high risk vs. unselected), timing of the ultrasound scan, expertise of the operator, quality of the
ultrasound equipment, extent of follow-up, and ascertainment of congenital anomalies. For major urinary
tract anomalies, 57% were detected before 24 weeks.
Lethal urinary tract anomalies account for 10% of pregnancy terminations.
19
A systematic approach to the prenatal diagnosis of
urinary tract abnormalities includes assessment of amniotic fluid volume, localization and characterization of
urinary tract abnormalities, assessment of fetal gender,
and search for associated abnormalities.
Normal AFV in the second half of pregnancy implies
at least one functioning kidney and a patent urinary
conduit to the amniotic cavity. If oligohydramnios is
1
1358 PART IV ■ Obstetric Sonography
present without a history of ruptured membranes, maternal drug intake (e.g., ACE inhibitors,
receptor antagonists,
inhibitors,
cocaine
22
nonsteroidal anti-inflammatory drugs,23
24
), or evidence of intrauterine growth restriction
21
COX-2 selective and nonselective
20
angiotensin II
(IUGR), urinary tract anomalies must be strongly suspected. In the setting of a urinary tract abnormality,
normal AFV indicates a good prognosis. Oligohydramnios in the early second trimester carries a very poor
prognosis because of the associated pulmonary hypoplasia. Occasionally and paradoxically, polyhydramnios
may occur, especially with unilateral obstructive uropathy, with mesoblastic nephroma, or when there are concomitant abnormalities of the central nervous system
(CNS) or gastrointestinal (GI) tract.
The following questions are helpful in defining and
characterizing the urinary tract abnormality:
• Is the bladder identified and normal in appearance?
• Are kidneys present? Are they normal in position,
size, and echogenicity? Are renal cysts identified?
• Is the urinary tract dilated? If so, to what degree, at
which level, and what is the cause?
• Is the involvement unilateral or bilateral,
symmetrical or asymmetrical?
• What is the fetal gender?
It is important to perform a detailed anatomic scan to
search for associated abnormalities, which may indicate
the presence of a syndrome or chromosomal abnormality. Renal anomalies may be part of the VATER associa-
tion (vertebral defects, anal atresia, tracheoesophageal
fistula, radial defects and renal anomalies). An expansion
of this syndrome, VACTERL, includes cardiac and non-
radial limb defects. When there are additional malformations, the risk for fetal chromosomal abnormalities is
substantially increased compared to the maternal agerelated risk: 30 times higher for multiple defects versus
3 times higher for isolated renal defect.
25
In addition, renal ultrasound is recommended for
parents (and siblings) of fetuses suspected to have certain
renal abnormalities (polycystic kidney disease, renal
agenesis or severe dysgenesis), because it may help to
diagnose the type of polycystic kidney disease in the
fetus, detect asymptomatic renal pathology in parents
(and siblings), and counsel parents regarding the recurrence risk.
26,27
Bilateral Renal Agenesis
Bilateral renal agenesis is a lethal congenital anomaly
with an incidence of approximately 1 in 4000 births and
a 2.5:1 male preponderance.
28
The ureteric bud fails to
develop; nephrons do not form; no urine is produced;
and severe oligohydramnios results. Pulmonary hypoplasia is the major cause of neonatal death. Other features
of “Potter’s sequence” include typical facies (beaked
nose, low-set ears, prominent epicanthic folds, hypertelorism), limb deformities, and IUGR.
EVALUATION OF THE FETAL
URINARY TRACT
Bladder
Presence
Appearance and size
Kidneys
Presence
Number
Position
Appearance (echogenicity, cysts)
Unilateral or bilateral
Collecting System
Dilation
Level of obstruction
Cause of obstruction
Unilateral or bilateral
Fetal Gender
FIGURE 39-4. “Lying down” adrenal sign. Longitudi-
nal scan through the renal fossa shows absence of the kidney and
the flattened adrenal gland (arrows). The lying-down adrenal sign
is an indication of renal agenesis or ectopia.
The ultrasound findings include severe oligohydramnios and nonvisualization of the kidneys and bladder.
Before 16 weeks’ gestation, AFV is not dependent on
urine production and may be normal despite absent
renal function. The absence of fetal kidneys should
be the most specific finding, but this may be difficult
to document because of poor image quality associated
with oligohydramnios. In addition, bowel or adrenal
glands in the renal fossae may be mistaken for kidneys.
29
However, recognition of the distinctive, flattened appearance of the adrenal gland on longitudinal sonogram
(“lying down” adrenal sign) helps to confirm that the
kidney did not develop in the flank
30
(Fig. 39-4).
Repeated and consistent nonvisualization of the
urinary bladder (over 1 hour) is a secondary sign of
FIGURE 39-5. Absent renal arteries. Color Doppler
ultrasound shows no renal artery arising from the aorta (Ao) in a
fetus with bilateral renal agenesis.
Chapter 39 ■ The Fetal Urogenital Tract 1359
FIGURE 39-6. Normal renal arteries. Color Doppler
ultrasound maps out the renal arteries bilaterally (arrows) in a
20-week fetus, confirming the presence of kidneys, which are
poorly visualized on this image.
A
FIGURE 39-7. Normal kidneys. T2-weighted MR images at A, 21 weeks’ gestation, and B, 30 weeks. The renal parenchyma (arrows)
shows low to intermediate signal intensity. The renal collecting system and bladder (B) shows high signal intensity. (A courtesy Sophia
Pantazi, MD, Mount Sinai Hospital, Toronto; B courtesy Susan Blaser, MD, Hospital for Sick Children, Toronto.)
bilateral renal agenesis. Conversely, identification of a
normal bladder excludes this diagnosis. A small urachal
diverticulum may mimic the bladder, but its lack of
filling and emptying distinguishes it from the bladder.
Furosemide challenge is not a useful test because it does
not reliably distinguish between fetuses with renal agenesis and those with impaired renal function from other
causes (e.g., IUGR).
31
Other techniques have been proposed to improve
visualization of fetal structures: intra-amniotic and intraperitoneal infusion of isotonic saline,
ultrasound,
33
and color Doppler ultrasound imaging.
32
transvaginal
34,35
B
The transvaginal probe is particularly useful in the
second trimester and with breech presentation. Color
Doppler imaging can be used to diagnose absent renal
arteries, providing further evidence for the diagnosis of
bilateral renal agenesis (Fig. 39-5). More importantly, it
helps to map out the renal arteries in difficult cases of
oligohydramnios, thereby confirming the presence of
kidneys and avoiding confusion (Fig. 39-6).
Fetal magnetic resonance imaging (MRI) may
help to identify the kidneys when sonographic visualization is limited by anhydramnios (or severe oligohydramnios) and large maternal body habitus
36,37
(Fig. 39-7).
1360 PART IV ■ Obstetric Sonography
BILATERAL RENAL AGENESIS
SONOGRAPHIC FINDINGS
Severe oligohydramnios
Absent kidneys
“Lying down” adrenal sign
Absent renal arteries on color Doppler imaging
Nonvisualization of bladder (over 1 hour)
TECHNICAL LIMITATIONS
Poor image quality caused by oligohydramnios
Fetal position (breech presentation)
PITFALLS IN INTERPRETATION
Amniotic fluid volume may be normal before 16
weeks’ gestation.
Bowel or adrenal glands can be mistaken for
kidneys.
Urachal diverticulum may mimic the bladder.
Empty bladder may be caused by impaired renal
function from other causes.
However, the image quality of MRI is also affected
by patient size and oligohydramnios, although to a
lesser degree. Therefore, it may be difficult for MRI to
exclude renal agenesis, if the kidneys are not seen before
24 weeks’ gestation. Associated anomalies are quite
common, including genital, cardiac, skeletal, and GI
abnormalities.
In the majority of cases, bilateral renal agenesis is a
multifactorial disorder. Parents should be counseled
about two risks. First, the recurrence risk of having
another child with bilateral renal agenesis is approximately 4%.
26,38
Second, parents and “unaffected” siblings have an increased risk of having silent genitourinary
malformations; 9% of first-degree relatives have asymptomatic renal malformations, most often unilateral renal
agenesis. Therefore, screening family members with
renal ultrasound is recommended.
26
Unilateral Renal Agenesis
Unilateral renal agenesis is three to four times more
common than bilateral renal agenesis, occurring 1 in
1000 births.
2
It may be difficult to diagnose prenatally
because AFV is normal and the bladder appears normal.
A common pitfall is failure to image the renal fossa in
the far field because of acoustic shadowing from the
spine, especially in the transverse plane. Meticulous
attention to technique is necessary (rotating the transducer, changing the maternal position, or repeated
observations). If a kidney is not found in the renal fossa,
most are either congenitally absent or ectopic.
39,40
The
contralateral kidney may be enlarged because of compensatory hypertrophy.41 There is a high incidence of contralateral renal abnormalities, the most common being
vesicoureteral reflux (VUR).42 Unilateral renal agenesis
may be associated with genital, cardiac, skeletal and GI
abnormalities. Isolated unilateral renal agenesis has a
good prognosis. Neonatal urologic workup is necessary,
including a voiding cystourethrogram.
The recurrence risk to parents of a baby with isolated
unilateral renal agenesis is about 1% if the parents have
normal renal ultrasound. However, if one parent has a
congenital solitary kidney, the risks to offspring are 7%
for congenital solitary kidney and 1% for bilateral renal
agenesis.
43
Renal Ectopia
One or both kidneys may be in an abnormal position.
The incidence of renal ectopia varies between 1:500 and
1:1200 births, with pelvic kidney being the most
common form.
44
The ectopic kidney may be hypoplastic
or dysplastic. When the renal fossa is empty, careful
scanning may demonstrate the ectopic kidney adjacent
to the bladder or iliac wing. Less frequently, the ectopic
kidney is located on the opposite side of the abdomen
relative to its ureteral insertion into the bladder, resulting
in crossed renal ectopia with or without fusion. In most
cases the crossed kidney fuses with the normally located
kidney (cross-fused ectopia), and an enlarged bilobed
kidney is seen. Renal ectopia is associated with a high
incidence of urologic abnormalities, most often VUR.
It may be associated with genital, skeletal, and GI
abnormalities. Neonatal urologic workup is necessary,
including renal ultrasound, technetium-99m succimer
99m
Tc DMSA) scan and a voiding cystourethrogram (in
(
renal ectopia with pelvic dilation and in crossed renal
ectopia).
45
Horseshoe Kidney
Horseshoe kidney is the most common fusion anomaly
of the kidney, occurring 1:400 to 1:500 births.
2,44
Prenatal sonographic findings include abnormal longitudinal axis of both kidneys and a bridge of renal tissue
connecting the lower poles (Fig. 39-8). Despite its relative frequency, this disorder is seldom diagnosed because
the findings are subtle, and surrounding bowel can
obscure the fused isthmus. The majority of horseshoe
kidneys have an abnormal anterior orientation of the
renal pelvis bilaterally. Measurement of the renal pelvic
angle on a true axial image of both kidneys is useful for
diagnosis, and angles less than 140 degrees are highly
suggestive of horseshoe kidney.
46
A horseshoe kidney is
frequently associated with other anomalies (e.g., urogenital, cardiac, skeletal, CNS) and chromosomal abnormalities such as Turner syndrome, trisomy 18, and
trisomy 9. Isolated horseshoe kidney is a relatively
benign disorder that requires postnatal urologic followup because of higher prevalence of VUR, renal calculi,
urinary tract infections (UTIs), and hydronephrosis.
Chapter 39 ■ The Fetal Urogenital Tract 1361
Renal Cystic Disease
Renal cystic disease consists of a heterogeneous group
of hereditary, developmental, and acquired disorders.
Because of their diverse etiology, histology, and clinical
presentation, a widely accepted classification does not
exist. The Potter classification is based on histology and
does not take into account recent advances in molecular
biology and genetics.
47
A more recent approach is to
group the abnormalities based on underlying cell biology,
such as aberrant early development (with failure of
induction between ureteric bud and metanephric mesenchyme) or defects in terminal maturation.
48
The
aberrant early development group includes dysplastic
kidneys. Typical histopathologic changes characterize
renal dysplasia, including architectural distortion,
FIGURE 39-8. Horseshoe kidney. Coronal image shows
the bridge of renal parenchyma (arrows) connecting the lower
poles of the kidneys (RK, LK), anterior to the aorta (Ao).
metaplasia, and primitive glomeruli and tubules. Cystic
changes are not universal but can be found in most
forms of renal dysplasia.
49
Defects in terminal maturation are observed in polycystic kidney disease. Initial
nephron and collecting duct formation is unremarkable
in these kidneys, but cystic dilation of these structures
occurs later, causing secondary loss of adjacent normal
structures. We find the following classification simple
and practical:
1. Dysplastic cysts, including the isolated multicystic
dysplastic kidney and dysplastic kidney resulting
from early severe obstruction.
2. Hereditary cysts, including polycystic kidney
disease and the inherited syndromes.
3. Nondysplastic nonhereditary cysts, such as simple
cysts.
Multicystic Dysplastic Kidney
A multicystic dysplastic kidney (MCDK) is the most
common form of renal cystic disease in childhood and
represents one of the most common abdominal masses
in the neonate. The majority of cases are associated with
an atretic ureter and pelvoinfundibular atresia. The
kidney is replaced by multiple cysts of varying sizes.
Between the cysts is a dense stroma, but usually no
normal renal parenchyma. MCDK is almost always
nonfunctional, so the prognosis depends entirely on the
contralateral kidney. Multicystic renal dysplasia usually
affects the whole kidney. However, it can be segmental
and can occur in the portion of the duplex kidney
supplied by the atretic ureter.
The sonographic findings correlate with the gross
pathologic appearance. The malformed kidney is usually
enlarged but may be normal or small. There are multiple
cysts of varying sizes that do not communicate with each
other and are randomly distributed (Fig. 39-9). Large
peripheral cysts distort the reniform contour. The renal
A B
FIGURE 39-9. Unilateral multicystic dysplastic kidney. A, Image of the fetus at 20 weeks’ gestation demonstrates multiple
small cysts in a slightly enlarged kidney (calipers); B, bladder. B, Follow-up image at 28 weeks’ gestation demonstrates a greatly enlarged
kidney (calipers). Cysts have increased in size, do not communicate, and are randomly distributed.
1362 PART IV ■ Obstetric Sonography
pelvis and ureter are usually atretic and not visible. On
color Doppler evaluation, the renal artery is either absent
or very small. Occasionally, a MCDK with a large central
cyst and small peripheral cysts can mimic hydronephrosis from ureteropelvic junction (UPJ) obstruction (see
later discussion). In hydronephrosis, however, the dilated
calyces are of uniform size and anatomically aligned and
communicate with the dilated renal pelvis. The kidney
usually maintains the reniform contour, with renal
parenchyma present peripherally.
The appearance and size of the MCDK may change
markedly over time (Fig. 39-9). On serial examinations,
the kidney and its cysts may increase or decrease in size
or may initially enlarge and later involute.
50
This variable
appearance may result from residual renal function and
progressive fibrosis.
Assessment of the contralateral kidney is very important. In utero, multicystic renal dysplasia is bilateral in
19% to 24% of cases
51,52
(Fig. 39-10). In unilateral multicystic renal dysplasia, 13% to 26% is associated with
contralateral renal abnormalities, including renal agenesis and UPJ obstruction.
51,53
In fetuses with MCDK,
severe oligohydramnios, and nonvisualization of the
urinary bladder imply lethal renal disease, either bilateral
MCDK or contralateral renal agenesis. Normal AFV
is reassuring. If there is contralateral hydronephrosis,
follow-up ultrasound is necessary to monitor any progressive dilation or oligohydramnios that may affect
obstetric management. Unilateral MCDK, without associated renal or nonrenal abnormalities, is associated with
a favorable outcome.
54
Because the incidence of VUR in
the contralateral kidney can be up to 23%, prophylactic
antibiotic therapy should be initiated soon after birth.
A complete urologic workup is necessary, including a
voiding cystourethrogram in the first month of life.
52
The natural history of MCDK is toward spontaneous
involution. This has been well documented both before
and after birth.
50,52
The longer the duration of follow-up,
the higher is the likelihood that the dysplastic kidney
will disappear completely. The risk of developing hypertension and malignancy in MCDK is low.
there is still controversy regarding routine prophylactic
nephrectomy.
53,56
Increasing evidence shows that the
complication rates are similar between children who did
and did not undergo neonatal nephrectomy.
vative management (long-term follow-up with serial
ultrasound) is favored in most centers.
48,55,56
55
However,
56,57
Conser-
Most cases
of MCDK are sporadic, with a low recurrence risk.
Obstructive Cystic Renal Dysplasia
Experimental work in lambs has shown that urinary
obstruction in the first half of gestation produces renal
dysplasia.
58,59
Unilateral disease can be caused by ureteropelvic or vesicoureteral junction obstruction. Bilateral
disease is caused by severe bladder outlet obstruction,
usually urethral atresia or posterior urethral valves. The
severity of renal dysplasia is related to the timing and
severity of obstruction to urine flow. The size of the
kidneys varies from small, normal, to greatly enlarged.
In some cases the enlargement is caused partly by the
presence of cysts and partly by hydronephrosis. Cysts are
usually present in the subcapsular area of the cortex. In
a fetus with obstructive uropathy, the sonographic identification of cortical cysts is indicative of renal dysplasia
(i.e., irreversible renal damage)
60
(Fig. 39-11). Dysplastic
kidneys may also demonstrate increased echogenicity
relative to the surrounding fetal structures, presumably
from abundant fibrous tissue (Fig. 39-12). However,
FIGURE 39-10. Bilateral multicystic dysplastic
kidneys. Transvaginal image in a 16-week fetus demonstrates
numerous small bilateral cysts (arrows) and no normal renal parenchyma. Note anhydramnios due to nonfunctioning kidneys.
FIGURE 39-11. Obstructive cystic dysplasia. Coronal
scan of fetus at 23 weeks with ureteropelvic junction obstruction
shows increased echogenicity of the kidney (calipers) with small
cortical cysts (arrows), indicative of irreversible renal damage.
FIGURE 39-12. Echogenic dysplastic kidney. Longi-
tudinal scan of fetus at 32 weeks with urethral obstruction. The
kidney (calipers) demonstrates increased echogenicity, with no
visible cysts. There is loss of corticomedullary differentiation.
With severe chronic obstruction, the kidney becomes dysplastic
and ceases to function. Note lack of pelvicaliectasis. S, Stomach.
increased cortical echogenicity is not a specific
finding,
60,61
and a diagnosis of renal dysplasia cannot be
made on the basis of increased parenchymal echogenicity
alone. Furthermore, it is important to recognize that not
all dysplastic kidneys have sonographically visible cysts
or increased cortical echogenicity, so one cannot accurately predict the absence of renal dysplasia. Renal function relates directly to the degree of dysplasia, which
determines the prognosis of patients surviving the perinatal period.
In general, if the obstruction is early and complete,
the renal parenchymal findings will be predominantly
macroscopic cysts and will simulate multicystic renal
dysplasia. Sonographic distinction between MCDK and
obstructive cystic renal dysplasia may be difficult, especially in the absence of hydronephrosis. In obstructive
cystic renal dysplasia, recognizable parenchyma surrounds the relatively small cysts, whereas in MCDK, no
normal renal parenchyma can be identified between
cysts. Obstructive cystic renal dysplasia most often occurs
with urethral obstruction. Therefore, sonographic evidence of urethral obstruction is helpful in suggesting the
diagnosis. In addition, renal dysplasia from lower urinary
tract obstruction frequently involves both kidneys, but
bilateral MCDK occurs in only 19% to 24% of cases.
51,52
Autosomal Recessive (Infantile)
Polycystic Kidney Disease
Autosomal recessive polycystic kidney disease (ARPKD)
involves both the kidneys and the liver. There is a wide
clinical spectrum, which varies from the perinatal form,
with severe renal disease, minimal hepatic fibrosis, and
early death from pulmonary hypoplasia, to the juvenile
Chapter 39 ■ The Fetal Urogenital Tract 1363
form, with minimal renal disease, marked hepatic fibrosis, and longer survival. Diffuse dilation of the renal
collecting tubules produces numerous 1-mm to 2-mm
cysts, predominantly in the medulla. Both kidneys are
enlarged, but a smooth contour is maintained. The cut
surface has a spongelike appearance, with small cysts that
tend to be arranged perpendicular to the renal capsule
(Fig. 39-13).
Sonography reveals bilateral reniform enlargement
of the kidneys (Fig. 39-13). There is poor delineation of
the intrarenal structures. The numerous tiny cysts are
usually smaller than the limit of sonographic resolution,
but they create multiple acoustic interfaces, accounting
for the characteristic increased renal echogenicity and
loss of corticomedullary differentiation.
60,62
Sometimes,
a peripheral hypoechoic rim may be seen, surrounding
the centrally increased echogenicity. When renal function is abnormal, there is oligohydramnios, and the
bladder is small or absent.
Autosomal recessive PKD may be diagnosed by ultrasound in the early second trimester based on the characteristic renal abnormalities, especially if the fetus is at
63
However, because of the variability in expression
risk.
and gestational age at onset, the kidneys may appear
normal initially, only becoming abnormal later.
63,64
Thus, a normal sonogram in a fetus at risk for ARPKD
does not exclude this disease, and prenatal diagnosis
using sonography can be unreliable, especially in early
pregnancy. Usually, but not always, ultrasound shows
evidence of recurrent ARPKD by 24 to 26 weeks’ gesta-
63,65
tion.
Couples who have a child with ARPKD have a
25% risk of having another affected child with each
subsequent pregnancy. ARPKD is caused by mutation
in the PKHD1 gene, which has been mapped to chro-
mosome 6p, allowing first-trimester genetic diagnosis in
at-risk families.
66
Autosomal Dominant (Adult)
Polycystic Kidney Disease
Autosomal dominant polycystic kidney disease (ADPKD)
is the most common of the hereditary renal cystic diseases. It is characterized by cyst formation in the kidneys
and liver. Cysts may also be present in the pancreas,
spleen, and CNS. In the early stage of the disease, only
a small percentage of nephrons show cystic dilation. In
the established adult disease, the kidneys are enlarged
and contain multiple cysts of varying sizes.
Autosomal dominant PKD typically is not recognized
in the fetal period because the kidneys typically appear
normal. In rare cases, ADPKD can present during
the fetal or neonatal period with symmetrically enlarged
hyperechogenic kidneys, within which small cysts
may be identified67 (Fig. 39-14). The bladder is usually
present, and AFV is often normal. In contrast to
ARPKD, where corticomedullary differentiation is
62
absent,
increased corticomedullary differentiation has
1364 PART IV ■ Obstetric Sonography
A
B
C
FIGURE 39-13. Autosomal recessive polycystic kidney disease. A, Coronal scan of a 27-week fetus shows enlarged kidneys
with increased echogenicity (arrows). Note anhydramnios. B, Photograph of cut surface of kidney shows a spongelike appearance. The
small cysts are very difficult to see. C, Photograph of whole-mount section shows small cysts that tend to be arranged perpendicular to
the renal capsule (hematoxylin and eosin stain). (B and C courtesy Sarah Keating, MD, Department of Pathology and Laboratory Medicine,
Mount Sinai Hospital, Toronto.)
68
been reported in ADPKD (20 of 27 cases).
Only a few
cases showed absent or decreased corticomedullary differentiation, and one case had normal corticomedullary
differentiation. Since the kidneys may appear normal in
the second trimester, follow-up scans are necessary in
fetuses at risk for ADPKD.
A family history of ADPKD is critical in making the
diagnosis of ADPKD in the fetus, because the recurrence
risk is 50%. In one review, however, only 38% of the
affected parents were aware of their disease before the
diagnosis in the affected child.
67
Therefore, ultrasound of
the parents’ kidneys is necessary (Fig. 39-14, D). When
there is a positive family history, prenatal diagnosis is
possible.
69
ADPKD is caused by mutation in three genes,
PKD1, PKD2, and PKD3. In 90% of cases, the condition
is linked to the PKD1 gene on chromosome 16p.
The prognosis for the fetus with ADPKD diagnosed
by ultrasound is uncertain because of limited data on
prenatal ultrasound findings and postnatal renal evolu-
70
The most useful indicator is the outcome of a
tion.
previously affected sibling, because there is a high degree
of correlation.
69
In the absence of a previously affected
pregnancy, counseling may be based on the following
data. Of 83 reported cases of ADPKD presenting in
utero (excluding termination of pregnancy) or in the first
few months of life, 43% died before 1 year.
69
Longitudinal follow-up studies of 24 survivors for a mean of 5
years showed that 67% developed hypertension, three of
whom had end-stage renal failure at a mean age of 3
71,72
years.
More recently, a series of 26 consecutive cases
demonstrated good prognosis in childhood, with 73%
remaining asymptomatic, 19% with hypertension, and
Chapter 39 ■ The Fetal Urogenital Tract 1365
A
C
FIGURE 39-14. Autosomal dominant polycystic kidney disease. A and B, Coronal and transverse scans of 19-week fetus
show slightly enlarged, echogenic kidneys (cursors). Note normal amniotic fluid volume and bladder (arrow). C, Coronal scan at 35 weeks
shows greatly enlarged kidneys (cursors).
D, Maternal autosomal dominant polycystic kidney disease. Classic ultrasound appearance of large kidney (cursors) with multiple cysts.
of which only two developed chronic renal insufficiency
during the 5-year follow-up.
They measure 9 cm in length, and multiple small cortical cysts (curved arrow) can be seen.
73
B
D
large and echogenic. Small, discrete cysts may be visible.
The diagnosis of Meckel-Gruber syndrome is particularly important for counseling future pregnancies in
Syndromes Associated with Renal
Cystic Disease
A number of rare inherited syndromes and genetic and
chromosomal disorders are associated with renal cystic
74
disease.
Approximately 30% of fetuses with trisomy 13
and 10% of fetuses with trisomy 18 have cystic kidneys.
Meckel-Gruber syndrome is a lethal autosomal
families not previously known to be at risk.
Recent genetic studies reveal that individuals with
renal cystic disease, other than ARPKD and ADPKD,
have a high prevalence of TCF2 gene anomalies, which
code for the hepatocyte nuclear factor-1 beta (HNF-1β)
transcription factor.
77,78
Individuals with these TCF2
anomalies may also demonstrate abnormalities of the
liver, pancreas, intestine and genital organs.
recessive disorder that carries a 25% risk of recurrence.
It can be detected by sonography at 11 to 14 weeks’
gestation, particularly in families with prior affected
pregnancies.
75
Sonographic diagnosis requires identifica-
tion of at least two features of the classic triad: cystic
dysplastic kidneys (present in almost 100% of cases),
occipital encephalocele (60%-85%), and postaxial
polydactyly (55%)
76
(Fig. 39-15). During second-tri-
mester sonography, it can be difficult to detect the
encephalocele and polydactyly because of the presence of
oligohydramnios. Microcephaly can be a useful clue to
the presence of an encephalocele. The kidneys are usually
Hyperechogenic (Bright) Kidneys
Hyperechogenic or “bright” kidneys seen on prenatal
ultrasound represent a diagnostic dilemma, particularly
in the presence of normal AFV (Fig. 39-16). Fetal
kidneys are considered hyperechogenic when they
appear more echogenic than expected, compared with
the adjacent liver or spleen. There is a wide differential
diagnosis,
evaluation of hyperechogenic kidneys
48,74
and the proposed algorithm is useful for
79
(Fig. 39-17). A
detailed examination of the fetus is necessary to search
1366 PART IV ■ Obstetric Sonography
A
B C
D E F
FIGURE 39-15. Meckel-Gruber syndrome. A to C, Ultrasound images of a 12-week fetus show classic features of Meckel-
Gruber syndrome: an occipital encephalocele (thick arrow), large echogenic kidneys (cursors), and postaxial polydactyly (thin arrow).
D to F, Postmortem photographs of the fetus (at 18 weeks’ gestation) demonstrate occipital encephalocele, large kidneys, and postaxial
polydactyly.
indicated to exclude aneuploidy (especially trisomy 13).
SELECT SYNDROMES ASSOCIATED
WITH RENAL CYSTIC DISEASE
If the kidneys and the biometric measurements are above
the 95th centile, an overgrowth syndrome (BeckwithWiedemann syndrome, Perlman syndrome) should be
Autosomal Dominant
Tuberous sclerosis
Von Hippel–Lindau disease (hemangioblastomas)
Autosomal Recessive
Bardet-Biedl syndrome (blindness, obesity,
polydactyly)
Jeune syndrome (asphyxiating thoracic dystrophy)
Meckel-Gruber syndrome (encephalocele and
polydactyly)
Short-rib polydactyly syndromes
Zellweger (cerebrohepatorenal) syndrome
X-Linked
Orofaciodigital syndrome type 1
Chromosomal
Trisomy 13
Trisomy 18
considered. In both conditions, there is generalized
organomegaly. AFV may be normal or increased. In
Beckwith-Wiedemann syndrome there may be macroglossia and omphalocele. In Perlman syndrome there
may be micrognathia and depressed nasal bridge.
In recent prospective and retrospective series of
prenatally diagnosed, isolated, bilaterally enlarged hyperechogenic kidneys, the most common underlying diagnosis was ARPKD, followed by ADPKD.
and AFI were the best predictors of perinatal outcome.
80,81
Kidney size
80
A detailed family history and an ultrasound examination
of the parents’ kidneys are important. In ADPKD, one
parent has the disease, and sonography usually establishes the diagnosis. Normal AFV favors ADPKD. In
ARPKD there is usually oligohydramnios, and there may
be a previously affected sibling.
Other, less common causes of enlarged hyperechogenic kidneys include Finnish nephrosis (an autosomal
recessive disorder that may be associated with elevated
for associated abnormalities. If there is sonographic evidence of urinary tract obstruction, renal dysplasia is a
possibility, especially when the kidneys are small or
normal in size and there are peripheral cortical cysts.
61
When other malformations are detected, karyotyping is
maternal serum alpha-fetoprotein levels), renal vein
thrombosis (usually unilateral), cytomegalovirus
(CMV) infection, nephrocalcinosis, and bilateral renal
tumors. In many cases a definitive diagnosis will require
postnatal investigations, including histology. Bilateral
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