CHAPTER 13 • The Fetal Urogenital System. First Trimester Ultr

 CHAPTER 13 • The Fetal Urogenital System

INTRODUCTION

The first trimester examination of the fetal urogenital system primarily focuses on the

demonstration of a fluid-filled bladder. When technically feasible or in specific highrisk conditions, visualization of both kidneys and fetal gender is attempted. With

optimal imaging, and after the 12th week of gestation, evaluation of the fetal urogenital

system is possible, but a conclusive diagnosis of normality requires confirmation later

on in pregnancy, because some malformations are not visible until the second trimester

or beyond. Several major urogenital malformations can be detected or suspected in the

first trimester, however, and are discussed in this chapter. In a large prospective

screening study for aneuploidies, including basic examination of fetal anatomy

performed in 45,191 pregnancies, the detection of anomalies of the urogenital system in

the first trimester was reported among the lowest of fetal malformations.1

EMBRYOLOGY

Understanding the embryogenesis of the urogenital system is important as it relates to

the evaluation of normal and abnormal anatomy. The urogenital system develops from

the intermediate mesoderm, which forms a urogenital ridge on each side of the aorta.

The urogenital ridge develops cranially to caudally into the pronephros, mesonephros,

and metanephros, respectively, representing three sets of tubular nephric structures. The

pronephros, the most cranial set of tubules, develops in the third week of embryogenesis

and regresses a week later. The mesonephros, located in the midsection of the embryo,

gives rise to the mesonephric tubules and the mesonephric ducts (Wolffian duct). The

mesonephric tubules regress, but the mesonephric ducts persist bilaterally and open into

the cloaca. The mesonephric ducts give rise to the ureters, renal pelves, and bladder

trigone. In the male, the mesonephric ducts also give rise to the vasa deferens,

epididymis, and seminal vesicles. An outgrowth of the caudal portion of the

mesonephric duct on each side forms the ureteric bud, which grows toward the

metanephric blastema, a mesenchymal condensation of metanephros (Fig. 13.1). Thedefinitive adult kidney is formed by the ureteric bud, which gives rise to the renal

pelvis, infundibula, collecting ducts, and calyces, and the metanephric tubules, which

form the nephrons with capillary invagination. With the growth of the embryo, the

kidney ascends from the pelvis into the upper retroperitoneum, and failure of renal

migration results in a pelvic kidney.

At about the seventh week of embryogenesis, a urogenital membrane grows caudally,

dividing the cloaca into ventral (urogenital sinus) and dorsal (rectum) components. The

urethra is derived from the endoderm at the ventral urogenital sinus. An invagination of

ectoderm in the most distal part of the urethra in males joins with the endodermal

epithelium of the proximal urethra to create a continuous channel. Differentiation of the

external genitalia into male and female occurs between the 8th and 11th week of

embryogenesis. Detailed development of the gonads and external genitalia is beyond the

scope of this chapter.

Figure 13.1: Schematic drawing of the embryologic development of the

urogenital system at around the seventh menstrual week. See text for details.Figure 13.2: Midsagittal plane of the fetus at 13 weeks of gestation showing

the bladder. This represents the same plane used for crown-length

measurement in the first trimester.

NORMAL SONOGRAPHIC ANATOMY

Visualization of the fetal urogenital system in the first trimester is performed by the

identification of the bladder and when possible the kidneys, which can be seen on

ultrasound as early as 10 weeks of gestation with high-resolution transvaginal

transducers.

Urinary Bladder

The fetal bladder appears as an anechoic structure in the anterior lower pelvis. The

bladder is easily seen in the sagittal view of the fetus, in the same plane used for the

crown-rump length (CRL) measurement (Fig. 13.2). The axial plane of the fetal pelvis

also demonstrates the fetal bladder in a central–anterior location (Fi g . 13.3).

Visualization of the bladder in the first trimester is aided by color Doppler ultrasound,

with the identification of the surrounding umbilical arteries (Fig. 13.4). Although the

fetal stomach is almost always filled with fluid, the fetal bladder is occasionally empty

in the first trimester and thus maybe difficult to image. When the fetal bladder is not

clearly demonstrated in the first trimester, the ultrasound examiner should reassess for

the presence of a bladder few minutes later to allow for bladder filling. The authors

therefore recommend that visualization of the fetal bladder is performed at the beginning

of the first trimester ultrasound examination in order to allow time for bladder filling if

the bladder is not visible then. The longitudinal length of the normal bladder should be

less than 7 mm in the first trimester (Fig. 13.5).2,3 The fetal bladder is seen on

ultrasound in about 88% of fetuses at 12 weeks of gestation and in 92% to 100% offetuses at 13 weeks of gestation.3,4

Kidneys and Adrenal Glands

With transabdominal ultrasound, the fetal kidneys are generally difficult to visualize and

differentiate from the surrounding bowel in the first trimester. Visualization of the fetal

kidneys by the transabdominal approach in the first trimester is improved with the use of

high-resolution transducers along with optimal scanning conditions (Figs. 3.2, 3.4, 13.6,

and 13.7). The transvaginal approach substantially improves visualization of the fetal

kidneys in the first trimester because of the proximity of the transducer to the fetal

abdomen and increased resolution of the probe (Figs. 3.2 and 13.8).4 The fetal kidneys

appear in the first trimester as rounded, slightly bright structures in the posterior

abdomen lateral to the spine, with the renal pelves noted as anechoic circles, centrally

within the renal tissue (Figs. 13.7 and 13.8). Cranial to both kidneys, the slightly

hypoechoic and large adrenal glands are seen (Fig. 13.7). The length of the adrenal

gland is less than half the length of the kidney.5 Visualization of the fetal kidneys in the

first trimester can be achieved in the coronal, sagittal, or axial planes (Fig. 13.9) of the

fetal abdomen. The coronal plane of the fetal abdomen is the optimal plane for first

trimester imaging of the kidneys in our experience (Figs. 13.7, 13.8B, and 13.10). This

coronal plane is also helpful for the demonstration of unilateral or bilateral renal

agenesis, and a more anterior view can demonstrate the presence of a horseshoe kidney

(see below). Color Doppler can also be added to demonstrate the right and left renal

arteries arising from the descending aorta (Fig. 13.10). The fetal kidneys can be

identified in 86% to 99% of fetuses at 12 weeks of gestation and in 92% to 99% of

fetuses at 13 weeks of gestation.4,6

Figure 13.3: Axial views of the fetal lower pelvis in three fetuses (A–C) at 13,

13, and 12 weeks of gestation, respectively. Note that the bladder is seen invarious stages of filing; with more filling in fetus A as compared to fetuses B

and C. The bladder is best demonstrated in this axial view at the level of the

pelvis. The addition of color Doppler, as shown in Figure 13.4, improves

bladder visualization.

Figure 13.4: Axial views in color Doppler of the fetal lower pelvis in two fetuses

(A and B) at 12 weeks of gestation. Note that the addition of color Doppler

shows the umbilical arteries surrounding the bladder. This axial view is helpful

for bladder imaging and also for confirming the presence of a three-vessel

umbilical cord. Compare with Figures 3.10, 13.33A and 13.34A..Figure 13.5: Schematic drawing (A) and corresponding ultrasound image (B)

of the midsagittal plane of the fetus showing the bladder in the lower pelvis.

The fetus in B is at 12 weeks of gestation. This midsagittal plane is used for

measuring the longitudinal diameter of the bladder. A normal bladder in the first

trimester should have a longitudinal diameter of less than 7 mm.

Genitalia

Although genitalia can be well seen either in an axial view of the pelvis or in the

midsagittal view during the measurement of the CRL, reliable differentiation of fetal

gender is of limited diagnostic accuracy in the first trimester. Embryologically, sex

differentiation is not fully completed until about the 11th week of gestation, and thus, sex

determination on ultrasound is relatively inaccurate before the 12th week of gestation.The ability to identify fetal gender on ultrasound increases with advancing gestation,

and the accuracy is enhanced after the 13th week of gestation or with CRL

measurements greater than 70 mm. The midsagittal view of the fetus is most reliable for

the identification of gender in the first trimester because it shows a caudally directed

clitoris in females (Fig. 13.11A and B) and a cranially directed penis in males (Fig.

13.11C and D). Labia majora and minora appear as parallel lines in females when

compared to a nonseptated dome-shaped structure, corresponding to the scrotum in

males. Accuracy of fetal gender determination in the first trimester varies from 60% to

100%, being inaccurate before 12 weeks, and reaches >95% after 13 weeks of

gestation.7

Figure 13.6: Right (A) and left (B) parasagittal planes of a fetus at 13 weeks

of gestation obtained with a high-resolution transabdominal transducer showing

fetal kidneys. In the right parasagittal plane (A), the right kidney can be seen

and appears as echogenic as the lung and is separated from the diaphragm by

the hypoechoic adrenal gland. In the left parasagittal plane (B), the left kidney

is seen under the left adrenal gland and stomach. The kidneys can also be

imaged in the first trimester in a coronal plane of the abdomen and pelvis (see

Figs. 13.7 and 13.8).Figure 13.7: Coronal planes of the fetal chest and abdomen, slightly anterior

plane to the coronal plane of the spine, in two fetuses (A and B) at 13 weeks

of gestation. The coronal plane in A is obtained transabdominally using a

convex transducer and the coronal plane in B is obtained transabdominally

using a high-resolution linear transducer. Note the clear delineation of both

kidneys because of the slight increase in echogenicity of renal tissue. Note that

both adrenal glands appear as triangular hypoechoic structures on the cranial

poles of the kidneys.Figure 13.8: Parasagittal (A) and coronal (B) planes of the abdomen and

pelvis, obtained transvaginally in two fetuses at 13 (A) and 11 (B) weeks of

gestation, respectively. Note in A and B that the kidneys are better visualized

using the transvaginal approach. Fetal kidneys typically appear more echogenic

in the first trimester, especially with the transvaginal approach, and thus it is

difficult at times to differentiate normal from abnormal kidney echogenicity in

early gestation (see Fig. 13.28).Figure 13.9: Axial planes of the fetal abdomen obtained transvaginally in two

fetuses at 12 (A) and 13 (B) weeks of gestation. Note the presence of fetal

kidneys in the posterior aspect of the abdomen. The cross-sectional plane is

ideally suited for the assessment of the diameter of the renal pelvis, measured

as a vertical diameter (double headed arrow). It is much easier to see the

kidneys in a cross section of the abdomen using the transvaginal approach. The

fetus in A is in a dorsoposterior position and the fetus in B is in a dorsoanterior

position.Figure 13.10: Coronal plane of the fetal abdomen and pelvis with color Doppler

in two fetuses at 13 (A) and 12 (B) weeks of gestation. Image in A is obtained

transabdominally and image in B is obtained transvaginally. The use of color

Doppler in a coronal plane of the abdomen and pelvis, as shown here in A and

B, demonstrates the two renal arteries arising from the aorta. This approach is

helpful in the presence of suspected unilateral or bilateral renal agenesis as the

absence of a kidney is associated with an absence of the corresponding renal

artery (see Figs. 13.33 and 13.34).Figure 13.11: In some clinical situations, it may be important to determine the

fetal gender in the first trimester. The anatomic orientation of the genitalia in

relation to the spine (white arrow) in the first trimester is helpful in that regard.

In female fetuses (A and B), the developing labia and clitoris have an

orientation that is parallel (pink arrow) to the longitudinal spine. In male fetuses

(C and D), the developing penis has an orientation that is almost perpendicular

(blue arrow) to the spine. Sex determination is more reliable after the 12th

weeks of gestation, when the crown-rump length is >65 mm.Figure 13.12: Schematic drawing (A) and corresponding ultrasound image (B)

of the midsagittal plane of the fetus, showing a dilated bladder with a bladder

longitudinal diameter of greater than 7 mm. Dilation of the bladder in the first

trimester fetus is defined by a longitudinal diameter of 7 mm or greater and is

referred to as megacystis or megavesica (see text for details). The presence

of megacystis with bladder longitudinal diameter between 7 and 15 mm is

associated with fetal aneuploidy, renal abnormalities, albeit a large number of

fetuses with bladder diameter between 7 and 15 mm are normal.Figure 13.13: Schematic drawing (A) and corresponding ultrasound image (B)

of the midsagittal plane of the fetus, showing a dilated bladder (megacystis)

with a bladder longitudinal diameter of greater than 15 mm. The presence of

megacystis with bladder longitudinal diameter of greater than 15 mm is

associated with fetal aneuploidy and renal abnormalities, along with distension

of the anterior abdominal wall. See text for details.

UROGENITAL SYSTEM ABNORMALITIES

Megacystis and Lower Urinary Tract Obstruction

Definition

The term megacystis is used to describe an unusually dilated bladder (Figs. 13.12 and13.13). Megacystis is defined in the first trimester by a longitudinal bladder diameter of

7 mm or more obtained on a midline sagittal plane of the fetus.2,3 Spontaneous

resolution of megacystis has been described when the longitudinal bladder length is less

than 15 mm and in the absence of associated chromosomal abnormalities.8 In the first

large study on megacystis between 10 and 14 weeks,3 145 fetuses with a bladder length

≥7 mm were evaluated: In the group with bladder length between 7 and 15 mm (Fig.

13.12), the incidence of chromosomal defects was 23.6% versus 11.4% for a bladder

diameter >15 mm (Figs. 13.13 and 13.14).3 In the remaining group with bladder

diameter between 7 and 15 mm and normal chromosomes, 90% showed spontaneous

resolution and 10% developed renal problems. In contrast, in all fetuses with a bladder

diameter >15 mm and normal chromosomes, megacystis progressed into obstructive

uropathy (Fig. 13.14).3

Figure 13.14: Axial (A) and sagittal (B) planes of the fetal pelvis, obtained

transvaginally in a fetus at 12 weeks of gestation with significant megacystis.

Megacystis occurs more commonly in male fetuses. See text for details.Figure 13.15: A: A midline sagittal plane of a fetus at 12 weeks of gestation

with megacystis, with a longitudinal bladder diameter of 12 mm. B: The

corresponding axial plane at the level of the pelvis at 12 weeks of gestation

showing the presence of a keyhole sign, suggesting a posterior urethral valves.

The fetus had no additional anatomic or chromosomal abnormalities. C: The

follow-up ultrasound at 14 weeks of gestation showing resolution of the

megacystis with a longitudinal bladder diameter of 6 mm. D: An axial plane of

the pelvis in color Doppler at 18 weeks of gestation showing normal bladder

and umbilical arteries with no bladder wall hypertrophy, as evidenced by the

proximity of the umbilical arteries to the internal bladder wall (arrows).

Resolution of first trimester megacystis is a common event. Compare with

Figure 13.16.

As noted, megacystis in the first trimester can be transient (Figs. 13.15 and 13.16),

but can also be a sign of a lower urinary tract obstruction (LUTO). LUTO, previously

referred to as bladder outlet obstruction, is an abnormality involving an obstruction of

the lower urinary tract at the level of the urethra, resulting from either a membrane-like

structure (valves) in the posterior urethra or urethral atresia. LUTO is usually sporadic,

and when severe, it is associated with oligohydramnios, pulmonary hypoplasia, andrenal damage. Posterior urethral valves (PUV), which represent the most common form

of LUTO, affect males almost exclusively with varying degrees of obstruction. Urethral

atresia on the other hand occurs in males and females and is extremely rare.

PUV occurs in about 1:8,000 to 1:25,000 of males,9,10 and its etiology is thought to

result from either an exaggerated development of the urethral folds (type 1 and 2) or

failure to create a continuous channel within the urethra with the persistence of an

obstructive urogenital membrane (type 3).10 Prenatal therapeutic interventions with

placement of a vesicoamniotic shunt or ablation of the obstructive tissue through

cystoscopy is reserved to the second trimester of pregnancy. Transient megacystis and

PUV will be the primary focus of discussion in this segment.

Ultrasound Findings

Megacystis is probably the easiest and most commonly diagnosed abnormality of the

genitourinary system in the first trimester. It is based on the identification of a large

bladder, measuring 7 mm or more in sagittal view (Figs. 13.12 to 13.15). In some cases

of resolving megacystis, a thickened bladder wall may still be observed (Fig. 13.16C

a nd D). The presence of progressive obstructive uropathy is common when the

longitudinal bladder length measures greater than 15 mm (Figs. 13.13 and 13.17).3Figure 13.16: A: A parasagittal plane of a fetus at 12 weeks of gestation with

megacystis, with a longitudinal bladder diameter of 11 mm. B: A parasagittal

plane of the same fetus at 13 weeks of gestation demonstrating a normal

bladder size and echogenic bladder wall. Chorionic villous sampling in this male

fetus showed no aneuploidy. C: An axial plane of the pelvis at 13 weeks of

gestation showing bladder wall hypertrophy, with bladder wall thickness of 1.8

mm. D: An axial plane of the pelvis in color Doppler at 13 weeks of gestation

confirming the presence of bladder wall hypertrophy as evidenced by the

distance between the umbilical arteries and the internal bladder wall (double

headed arrow).Figure 13.17: Sagittal planes of the fetal abdomen and pelvis in the first

trimester, in four fetuses (A–D) with megacystis (asterisks), exceeding 15 mm

in longitudinal diameter. This finding is associated with significant risk for

aneuploidy and renal abnormalities. Amniotic fluid appears normal in all fetuses,

as expected in the first trimester in the presence of significant uropathy, and

oligohydramnios is not expected before 16 weeks of gestation. Note the

presence of keyhole sign in D (arrow). Follow-up ultrasound examinations often

demonstrate the presence of renal abnormalities and underdeveloped lungs,

expected here in fetuses B, C, and D because of significant megacystis with

abdominal wall distention.Figure 13.18: Three-dimensional ultrasound in surface mode in a fetus with

megacystis and trisomy 13 at 13 weeks of gestation. Note the presence of

normal amniotic fluid volume surrounding the fetus (A–C). Also note the

presence of distended abdominal wall (arrows) in A. In B, the anterior

abdominal wall and bladder were opened digitally using postprocessing volume

cutting tools to provide an insight into the dilated bladder. C: Postprocessing

with transparency tool (silhouette ®), thus facilitating the visualization of the

megacystis.

The sonographic identification of PUV is possible in the first trimester, especially in

severe cases (Figs. 13.17 and 13.18). In the first trimester, amniotic fluid is commonly

normal in PUV cases, and the diagnosis is typically suspected by the presence of an

enlarged bladder (megacystis) (Figs. 13.17 and 13.18). PUV in the first trimester is

often associated with hydronephrosis and renal dysplasia in severe cases (Figs. 13.19

and 13.20). PUV markers of poor prognosis, such as the presence of renal cortical cysts

and increased renal echogenicity, are already present in the first trimester (Fig. 13.19),

but their absence cannot predict a good prognosis. The keyhole sign, related to a dilated

proximal urethra, supports the diagnosis of PUV in the first trimester (Figs. 13.15B,

13.17D, 13.20B, and 13.21B).Figure 13.19: Axial plane of the fetal pelvis in a fetus at 13 weeks of gestation

with megacystis, posterior urethral valves, and trisomy 13. Note the presence

of urinary tract dilation (UTD) (double headed arrows) and increased renal

parenchyma echogenicity, suggesting the presence of renal dysplasia. In this

case, it is not feasible to relate the presence of increased renal parenchyma

echogenicity to urologic obstruction or trisomy 13.

Associated Malformations

Megacystis in the first trimester has been associated with chromosomal malformations,

primarily trisomy 13 and 18.3 Outcome of persistent megacystis in the first trimester is

poor compared with second and third trimesters.11,12 Associated malformations are seen

in about 40% of PUV fetuses, and chromosomal abnormalities occur in 10% to 24% of

cases.3 In chromosomally abnormal fetuses, thickened nuchal translucency and

intracerebral, facial, or cardiac anomalies are common. In a recently published large

study on 108,982 first trimester fetuses including 870 fetuses with abnormal karyotypes,

megacystis was found in 81 fetuses for a prevalence of 1:1,345.13 Of all fetuses with

megacystis, 63/81 (77.7%) had a bladder length between 7 and 15 mm, with the

remainder (18/81; 22.3%) having a bladder larger than 15 mm. The rate of aneuploidy

in megacystis was 18% (15/81) and, in this study, was similar in both subgroups.13

Interestingly, aneuploidies in megacystis were almost equally distributed between

trisomy 18 (33%), trisomy 13 (27%), trisomy 21 (27%), and others (20%).13

Differential diagnosis includes urethral atresia, megacystis microcolon intestinalhypoperistalsis syndrome, which occurs in 75% in female fetuses, cloacal

malformation, and other cystic anomalies in the pelvis (Figs. 13.22 and 13.23).14

Figure 13.20: Axial view of the upper (A) and lower (B) pelvis in a fetus with

megacystis because of posterior urethral valves at 14 weeks of gestation. Note

the presence of a massively distended bladder (megacystis) in A and B and a

keyhole sign (circle in B) typical for the presence of urethral obstruction.

Urinary Tract Dilation

Definition

Urinary tract (UT) dilation is a term used to describe the presence of dilation of the

renal pelvis and occasionally the ureter. Terms such as pyelectasis, renal pelvis

dilation, and hydronephrosis have been used to describe dilation of the UT system. With

the apparent confusion associated with all these terms, a multidisciplinary consensus

panel recently recommended avoiding the use of nonspecific terms in describing UT

dilation, and proposed the consistent use of the term urinary tract dilation, or “UT

dilation,”15,16 which can also be used in the first trimester. The renal pelvis is

considered normal when it measures <4 mm at <28 weeks gestation and <7 mm at >28

weeks gestation.16 Although there are no specific measurements of the renal pelvis in

the first trimester, a cutoff of 1.5 mm was suggested in one study17 (Fig. 13.24). When

UT dilation is noted, additional sonographic features should be evaluated to include the

presence of calyceal dilation, renal parenchymal appearance and thickness, ureteral

dilation, and bladder abnormalities (see previous section). The evaluation for the

presence of many of these additional sonographic features is important in order to

further classify the severity of the UT dilation. It is important to note, however, that

these features are difficult to assess in the first trimester, and several may not be evident

until the second or third trimester of pregnancy. UT dilation is present in 1% to 5% ofpregnancies,15,18,19 with a 2:1 male-to-female prevalence.19

The presence of UT dilation in the first trimester is commonly a transient finding,

with resolution noted in a significant number of cases upon follow-up into the second

and third trimesters of pregnancy.18 The presence of UT dilation in the first trimester has

been associated with a slight increase in the risk for chromosomal anomalies (Figs.

13.25 and 13.26)17; it can also be a transient finding or can be associated with the

presence of UT dilation later in gestation (Fig. 13.27). A close follow-up in the second

trimester is thus recommended to document any progression or resolution. When UT

dilation persists into the neonatal period, ureteropelvic junction obstruction is the most

common associated abnormality followed by vesicoureteral reflux (VUR).15,16

Figure 13.21: Three-dimensional ultrasound in surface mode in two fetuses

with megacystis at 14 (A) and 13 (B) weeks of gestation. Postprocessing

volume cutting is performed in A and B to display the dilated bladders

(asterisks). Note the keyhole sign in fetus B, suggesting the presence of

posterior urethral valves.Figure 13.22: Sagittal views (A and B) of a fetus at 12 weeks of gestation

demonstrating the presence of suspected megacystis (asterisks) with a

longitudinal “bladder” diameter of 13 mm (B). Nuchal translucency (NT) was

thickened (3 mm) and tricuspid regurgitation was demonstrated (not shown).

Transvaginal ultrasound was performed (C and D) to better assess the

urogenital organs. Neither a keyhole sign nor abnormal kidneys were found,

and the cystic structure was noted to be located in the middle right abdomen

under the liver and cranial to a small bladder (C). Color Doppler confirmed the

presence of a small filled bladder, normally located between the two umbilical

arteries, as shown in D. The cystic structure was classified as a “cyst of

unknown origin.” Chorionic villous sampling revealed trisomy 21. Etiology of

abdominal cyst was not revealed because of pregnancy termination. L, Left; R,

right. See Figure 13.23.Figure 13.23: Three-dimensional ultrasound at 12 weeks of gestation, obtained

transvaginally of the same fetus (trisomy 21) as in Figure 13.22. A and B:

Multiplanar displays and C represents display in surface mode. A: A midsagittal

view with a large cyst (asterisk) mimicking megacystis. The corresponding

orthogonal coronal view in B shows that the cystic structure (asterisk) is

located laterally in the right abdominal cavity and not midline as expected in

megacystis. In C, postprocessing volume cutting tools are used to display the

cyst (asterisk) and visualize its proximity to the right abdominal wall (double

headed arrow). NT, nuchal translucency; L, Left; R, right.Figure 13.24: Axial planes of the fetal abdomen in two fetuses with urinary

tract dilation (UTD) at 12 (A) and 13 (B) weeks of gestation. The assessment

for the presence of UTD is obtained in an axial plane of the pelvis (A and B) by

measuring the renal pelvis in an anterior to posterior diameter as shown in B

(double headed arrow). A clear cutoff for UTD in the first trimester has not

been established yet and some suggested a cutoff of greater than 1.5 mm.

UTD in the first trimester can resolve spontaneously or be a marker of urinary

tract abnormalities or aneuploidy.Figure 13.25: Midsagittal plane of the fetal head (A) and axial plane of the

abdomen (B) in a fetus at 13 weeks of gestation with trisomy 21. Note in A the

presence of thickened nuchal translucency (3.3 mm) (asterisk) and absent

nasal bone (circle) and in B, urinary tract dilation (UTD) with an anterioposterior

diameter of 3.6 mm. (Measurement not shown).Figure 13.26: Coronal (A) and axial (B) planes, obtained transvaginally, in a

fetus at 13 weeks of gestation with urinary tract dilation (UTD) (arrows). This

patient was referred for diagnostic testing because of maternal balanced

translocation. The patient decided to wait for amniocentesis. Follow-up

transabdominal ultrasound at 17 weeks of gestation (C and D) shows the

persistence of UTD (arrows). Amniocentesis revealed the presence of an

unbalanced translocation in the fetus. Asterisk points to the stomach in A and

C.Figure 13.27: Axial planes of the fetal abdomen in the same fetus at 13 (A)

and 22 (B) weeks of gestation with fluid accumulation in the renal pelves

(arrows). The presence of fluid in the renal pelves helps to identify kidneys in

the first trimester on transabdominal ultrasound (A). No other associated

abnormalities were seen, and isolated urinary tract dilation was confirmed

postnatally.

Ultrasound Findings

Using the transvaginal approach, the renal pelvis can be demonstrated in the first

trimester as an anechoic center, surrounded by renal parenchyma. When UT dilation is

present in early gestation, it can be recognized on abdominal ultrasound as well (Fig.

13.26). The ideal technique for the measurement of the renal pelvis is based on images

of the kidney obtained from an axial plane of the fetus in an anterior–posterior

orientation, with optimal measurements obtained with the fetal spine at the 12 or 6

o’clock positions (Figs. 13.9 and 13.24). In addition, the measurement should be taken

in an anterior to posterior orientation of the pelvis at the maximal diameter of the

intrarenal pelvis dilation.16 The calipers should be placed on the inner border of the

fluid collection. Evaluating the fetal kidneys in the coronal and parasagittal approach

enhances visualization, especially when the fetal spine shadows a posterior kidney (Fig.

13.26). Ureteral dilation is rarely seen in the first trimester, and its presence should

suspect LUTO. Grading of the renal pelvis dilation is not applicable in the first

trimester because most noted dilations are mild and are not associated with calyceal

abnormalities. Amniotic fluid volume is commonly normal in association with renal

pelvis dilation in the first trimester.

Associated MalformationsAssociated malformations typically involve chromosomal anomalies and abnormalities

of the urogenital system. The presence of renal pelvis dilation in the first trimester of

pregnancy has been described as a soft marker for trisomy 21, similar to the second

trimester.17,20 When UT dilation is noted in the first trimester, further assessment of

aneuploidy risk with nuchal translucency, biochemical markers, or cell-free DNA along

with a comprehensive anatomic survey is an important step in pregnancy management.

Follow-up ultrasound examination in the second trimester is essential to assess fetal

anatomy in more detail. Differential diagnosis of UT dilation includes transient finding,

ureteral–pelvic or vesicoureteral junction obstruction, vesicoureteral reflux, PUV, or

other urogenital malformations.

Hyperechogenic Kidneys

Definition

The term “hyperechogenic kidneys” is used in the second trimester to describe

increased echogenicity of the renal parenchyma, typically with renal tissue appearing

more echogenic than the surrounding liver. As stated in the section on normal anatomy,

the kidneys appear slightly more echogenic in the first trimester than later on in

pregnancy. There is currently no objective definition on what represents hyperechogenic

kidneys in the first trimester, and the diagnosis is based on subjective assessment of

experienced operators (Fig. 13.28). Indeed, improvement in ultrasound technology has

resulted in improved tissue characterization in the first trimester and, in some cases, in

increased echogenicity of kidneys. The suspicion of hyperechogenic kidneys is

particularly relevant in pregnancies at high risk for renal disease because of the

presence of additional ultrasound signs (Figs. 13.28 to 13.30) or to a prior family

history (Figs. 13.30 to 13.32). As in the second trimester, hyperechogenic kidneys can

be a transient finding, but may also be a marker for renal abnormalities. Detailed

sonographic evaluation of the fetus and follow-up examinations are recommended when

hyperechogenic kidneys are noted in the first trimester of pregnancy.Figure 13.28: As noted previously, the normal fetal kidneys appear slightly

hyperechogenic in the first trimester, especially on transvaginal ultrasound (see

Figs. 13.6 to 13.8). Increased echogenicity of fetal kidneys in the first trimester

can be a sign of associated renal dysplasia, aneuploidy, or cystic renal

disease. A and B: Hyperechogenic kidneys (arrows) in the first trimester in

association with posterior urethral valves. C and D: Hyperechogenic kidneys

(arrows) in the first trimester in association with trisomy 13. See also Figures

13.29 to 13.32.Figure 13.29: Axial plane of the head (A) and coronal plane of the abdomen in

a fetus with trisomy 13 at 12 weeks of gestation. Note the presence of

holoprosencephaly in A. Facial dysmorphism, cardiac anomaly, and other

abnormalities were also seen on ultrasound (not shown). Note in B, the

presence of hyperechogenic kidneys, a common finding in trisomy 13.Figure 13.30: Meckel–Gruber syndrome in a fetus at 13 weeks of gestation.

Note the presence of bilaterally enlarged polycystic kidneys, seen

transabdominally in A and C and transvaginally in B. The large kidneys lead to

the distension of the abdomen (A–C). D: An axial plane of the lower pelvis in

color Doppler shows the two umbilical arteries with no bladder seen in

between. Amniotic fluid is still normal at this gestation and typically disappears

around 16 weeks. This pregnancy was the result of consanguineous couple

with recurrence risk of 25%.Figure 13.31: Midsagittal plane (A) and coronal plane (B) of a fetus with

Meckel–Gruber syndrome at 13 weeks of gestation. Note in A the presence of

an occipital encephalocele and in B the presence of bilateral polycystic kidneys

(arrows). Similar to the pregnancy in Figure 13.30, amniotic fluid is still present.

Figure 13.32: A: A parasagittal plane of the abdomen at 25 weeks of gestation

in a fetus with autosomal recessive polycystic kidney disease (ARPKD),

showing one of the two enlarged hyperechogenic kidneys with the typical

texture of microcystic dysplasia (arrows). The baby died shortly after birth and

ARPKD was confirmed genetically with carrier status in both parents. B: A

coronal plane of the abdomen in the next pregnancy at 12 weeks of gestation,

showing normal size kidneys (one shown—arrow) with mild hyperechogenicity:within the echogenicity range of normal kidneys in early gestation (compare

with Fig. 13.8). Genetic testing confirmed ARPKD and the pregnancy was

terminated.

Ultrasound Findings

Ideally, the kidneys should be visualized in a sagittal or coronal view in order to

demonstrate large segments of renal parenchyma and enable a comparison with the

surrounding lung, liver, and bowel. Enlarged hyperechogenic kidneys in the first

trimester are particularly concerning because of the possibility of polycystic kidney

disease or the association with aneuploidies (Fig . 13.29). The association of

hyperechogenic kidneys with UT dilation warrants follow-up in the second trimester

and can be seen with megacystis or PUV (Figs. 13.28 A and B).

Associated Malformations

Hyperechogenic kidneys in the first trimester have been described as a marker for the

presence of inherited autosomal recessive polycystic kidney disease (ARPKD).21 We

have also seen hyperechogenic, enlarged kidneys at 13 weeks of gestation in an affected

fetus of a mother with autosomal dominant polycystic kidney disease (ADPKD). It is

important to note, however, that the presence of ARPKD or ADPKD is not commonly

associated with hyperechogenic or enlarged kidneys in the first trimester. Figure 13.32

presents a case of ARPKD where the fetal kidneys appeared “normal” at 12 weeks of

gestation, but molecular genetics confirmed ARPKD, given a previously affected

sibling. Interestingly, other polycystic kidneys, such as in Meckel–Gruber syndrome

(Figs. 13.30 and 13.31), can be detected in the first trimester by the presence of

enlarged hypoechoic renal parenchyma with cysts. Hyperechogenic kidneys can also be

noted in the first trimester in the presence of renal dysplasia in association with PUV,

trisomy 13, or trisomy 18 (Figs. 13.28 and 13.29). Hyperechogenic kidneys are an

isolated finding in association with HNF1B (or TCF2) gene mutation, but the earliest

suspected case to date was reported at 18 weeks of gestation.22

Autosomal Recessive Polycystic Kidney Disease

Definition

ARPKD, also referred to as infantile polycystic kidney disease, is an autosomal

recessive disease involving cystic dilation of the renal collecting tubules with

associated congenital hepatic fibrosis. ARPKD is caused by mutation of the PKHD1

gene, located on the short arm of chromosome 6, with complete penetrance and variable

phenotypic expressivity, given the large size of the gene. The prevalence of ARPKD is

around 1:20,000 births.23 Disease manifestation in childhood or in adulthood is the most

common presentation.24,25 ARPKD is thus generally diagnosed prenatally after 20

weeks of gestation or in the neonatal period in only 30% of cases.24,25 ARPKD can be

isolated, but is also found in association with syndromic diseases of the group ofciliopathies. Out of the ciliopathies group is Meckel–Gruber syndrome, with the triad of

polycystic kidneys, encephalocele, and polydactyly (Figs. 13.30 and 13.31).

Ultrasound Findings

The classic ultrasound findings in ARPKD in late second trimester are symmetrically

enlarged hyperechogenic kidneys (Fig. 13.32A) that fill the fetal abdomen and in some

conditions in association with oligohydramnios and absent bladder. The prenatal

diagnosis of ARPKD has been observed in early gestation around 14 weeks,21 owing to

increased hyperechogenicity, but most cases become apparent only after 25 weeks when

kidney enlargement occurs (Fig. 13.32A). The presence of normal appearing kidneys in

early gestation, however, does not rule out ARPKD even in previously affected families

(Fig. 13.32B). When normal or mildly hyperechogenic kidneys are noted in the first

trimester in at-risk families, follow-up ultrasound examinations into the second and

third trimester is important because progression of ultrasound findings tend to occur

after mid-gestation. An empty bladder on repeated ultrasound examinations in the first

trimester was also reported as an important sign for ARPKD, with follow-up

examination in the second trimester revealing the diagnosis.1 In fetuses with Meckel–

Gruber syndrome, enlarged cystic kidneys are commonly seen in the first trimester along

with the presence of a posterior encephalocele and polydactyly21 (Figs. 13.30 and

13.31). Given the lack of morphologic manifestation of ARPKD before the second

trimester of pregnancy, along with its variable expressivity, the overall detection of

ARPKD in early gestation remains low.1

Associated Findings

Differential diagnosis of enlarged echogenic kidneys in the first trimester includes

normal variant, trisomy 13, trisomy 18, adult-onset polycystic kidney disease, Meckel–

Gruber syndrome, and/or other ciliopathies.

Autosomal Dominant Polycystic Kidney Disease

ADPKD is characterized by the presence of enlarged kidneys with multiple cysts of

variable size. ADPKD is one of the most common genetic disorders with recurrence

risk of 50% and is a common cause of renal dysfunction. The disease manifests itself in

adulthood, and the prenatal diagnosis of ADPKD is typically performed when a family

history of ADPKD is present. The presence of enlarged hyperechogenic kidneys can

occasionally be seen in early gestation, typically in the presence of a family history. The

presence of normal appearing kidneys in the first and second trimester of pregnancy,

however, is not uncommon in ADPKD.

Multicystic Dysplastic Kidney

Multicystic dysplastic kidney (MCDK) is a severe nonfunctioning renal malformation in

which the kidney contains multiple noncommunicating cysts of varying size, dense

central stroma, and an atretic ureter. The pathogenesis of MCDK is unknown. To our

knowledge, MCDK has not yet been diagnosed in the first trimester. Bilateral MCDK,which occurs in 25% of cases, is associated with oligohydramnios after about the 16th

week of gestation. The presence in the first trimester of an absent bladder on repeated

examinations is also possible, given the lack of renal function. The presence of

discrepancy in echogenicity of renal parenchyma between the right and left kidney on

transvaginal ultrasound is another marker for the possible presence of a unilateral

MCKD in early gestation. Unilateral MCDK is associated with contralateral renal

anomalies in 30% to 40% of cases and nonrenal anomalies in about 25% of cases.26

Extrarenal anomalies include central nervous system, cardiac, and gastrointestinal.26

The risk of aneuploidy is high when MCDK is associated with multiple extrarenal

malformations.

Bilateral Renal Agenesis

Definition

Bilateral renal agenesis is defined by the congenital absence of both kidneys and

ureters, and results from a developmental failure of the ureteric bud and/or the

metanephric mesenchyme. Bilateral renal agenesis has a prevalence of 1:4,000 to

1:7,000 pregnancies at the routine obstetric ultrasound examination.27 The absence of

both kidneys results in anhydramnios, which is typically first noted after 16 weeks of

gestation. Anhydramnios leads to Potter sequence, which is a constellation of findings

including pulmonary hypoplasia, facial abnormalities, and deformities of extremities.

Bilateral renal agenesis is more common in males and is a uniformly lethal

malformation.

Ultrasound Findings

The prenatal diagnosis of bilateral renal agenesis is a straightforward diagnosis after 16

weeks, because of associated oligohydramnios, as a leading ultrasound clue. The onset

of oligo- or anhydramnios starts between 15 and 16 weeks of gestation when amniotic

fluid production is primarily renal in origin. Therefore, the suspicion of bilateral renal

agenesis in the first trimester is a challenge and primarily relies on the identification of

an absent bladder and kidneys (Figs. 13.33 and 13.34). Absent bladder in the pelvis on

repeated ultrasound examinations may alert the examiner to the presence of bilateral

renal agenesis in the first trimester.28 Color Doppler applied on an axial view of the

pelvis will identify the two umbilical arteries and help to localize the anatomic site of

the bladder (Figs. 13.4, 13.33, and 13.34). On rare occasions, a small “bladder” maybe

visible in the pelvis in early gestation despite the presence of bilateral renal agenesis.

Although the exact etiology of this finding is currently unclear, possibilities include

retrograde filling of the bladder or the presence of a midline urachal cyst mimicking the

bladder.28 A coronal plane of the abdomen and pelvis in color Doppler will identify the

descending aorta and the absence of renal arteries (Figs. 13.33 and 13.34). The “lying

down” or “flat” adrenal sign, an important second trimester sign showing the flattened

adrenal gland on the psoas muscle, is not easily seen in the first trimester (Fig. 13.35).When bilateral renal agenesis is suspected in the first trimester, follow-up ultrasound in

the early second trimester is recommended to confirm the diagnosis by the onset of

anhydramnios.

Associated Malformations

Associated malformations have been frequently reported and include gastrointestinal,

vascular, and laterality defects. Several syndromes are associated with bilateral renal

aplasia to include VACTERL association, Fraser syndrome, and sirenomelia, to name a

few. Chromosomal aneuploidy is present in about 7% of prenatal cases,27 and several

causative gene mutations have been described. The absence of a bladder on ultrasound

in the first trimester should also alert the examiner to the presence of other urogenital

malformations such as bladder exstrophy or bilateral cystic renal dysplasia.1

Figure 13.33: Axial plane of the pelvis (A) and coronal plane of the abdomen

(B) in color Doppler in a fetus at 13 weeks of gestation with renal agenesis

diagnosed on routine first trimester ultrasound. Note in A the absence of a

bladder between the two umbilical arteries. In B, renal arteries could not be

imaged with empty renal fossa and absence of renal arteries bilaterally.

Amniotic fluid is normal. The presence of a pelvic kidney could not be ruled out,

and the patient had a follow-up ultrasound at 16 weeks of gestation (notdemonstrated) showing anhydramnios and confirming the diagnosis of bilateral

renal agenesis.

Figure 13.34: Axial plane of the pelvis (A) and coronal plane of the abdomen

(B) in color Doppler in a fetus at 13 weeks of gestation with renal agenesis.

Similar to Figure 13.33, note the absent bladder in A and empty renal fossa

with absence of renal arteries in B. This fetus also had radial aplasia (not

shown).Figure 13.35: Parasagittal plane of the fetal abdomen in two fetuses (A and B)

with empty renal fossa, diagnosed at 12 weeks of gestation in both fetuses.

Note the presence of the typical flat adrenal gland (labeled) in A and B and

compare with the normal shape of the adrenal gland in Figure 13.7. Fetus in A

also had a single umbilical artery, which led us to perform a transvaginal

detailed ultrasound. Unilateral renal agenesis was confirmed in fetus A at 17

weeks of gestation. Fetus in B had a cardiac defect, diagnosed at 12 weeks of

gestation and detailed first trimester ultrasound revealed the presence of an

empty renal fossa with flat adrenal gland (asterisk). The final diagnosis of a

pelvic kidney was made and is shown in Figure 13.36.

Unilateral Renal Agenesis

Unilateral renal agenesis results when one kidney fails to develop and is absent. This is

primarily because of failure of development of the ureteric bud or failure of induction of

the metanephric mesenchyme. The prenatal diagnosis in the first trimester is initially

suspected when one kidney is not seen in the renal fossa (Fig. 13.35). A search for a

pelvic kidney or crossed ectopia should be performed before the diagnosis of unilateral

renal agenesis is confirmed. Color Doppler of the abdominal aorta, obtained in a

coronal plane of the abdomen and pelvis, is helpful to confirm the diagnosis because it

shows the absence of a renal artery on the suspected renal agenesis side. In highresolution ultrasound, visualization of the renal fossa can reveal the presence of the

horizontal flat (lying down) adrenal gland instead of the kidney (Fig. 13.35). Follow-up

in the second trimester is important in order to confirm the diagnosis. Compensatoryhypertrophy of the contralateral kidney is present in the second and third trimester of

pregnancy. The diagnosis of a single umbilical artery in the first trimester presents an

increased risk for renal malformations.

Pelvic Kidney, Crossed Renal Ectopia, and Horseshoe Kidney

Abnormal kidney location, also referred to as renal ectopia, encompasses three types of

abnormalities: pelvic kidney, crossed renal ectopia, and horseshoe kidney. Abnormal

kidney location results from failure of proper migration of the metanephros from the

pelvis to the abdomen during embryogenesis. Pelvic kidney refers to a kidney that is

located in the pelvis below the aortic bifurcation (Fig. 13.36). Crossed renal ectopia

refers to two kidneys on one side of the abdomen, with fusion of the kidneys. Horseshoe

kidney, the most common form of renal ectopia, refers to fusion of the lower poles of the

kidneys in the midline abdomen, typically below the origin of the inferior mesenteric

artery (Fig. 13.37). Other renal abnormalities are common in association with renal

ectopia and include UT dilation. In the first trimester, the slightly bright appearance of

kidneys helps in the identification of kidney location in the pelvis when the renal fossa

appears empty (Fig. 13.36). Bridging of renal tissue over the fetal spine helps in the

identification of a horseshoe kidney in the first trimester (Fig. 13.37). In our experience,

the presence of trisomy 18, Turner syndrome, and single umbilical artery increases the

risk for an association with horseshoe kidneys (Fig. 13.37). Careful evaluation of fetal

anatomy in the first trimester is important when renal ectopia is suspected, given a high

association with other fetal malformations as VACTERL association, open and closed

spina bifida, and chromosomal abnormalities.

Duplex Kidney

Duplex kidney, also referred to as duplicated collecting system, occurs when a kidney is

divided into two separate moieties, an upper moiety and a lower moiety. Duplex kidney

is thought to occur during embryogenesis when an additional ureteric bud arises from

the mesonephric duct and fuses with the metanephric mesenchyme. The ureter arising

from the upper renal moiety is commonly dilated and may form an ureterocele in the

bladder, which is a common sign leading to its prenatal diagnosis. The renal pelvis of

the upper moiety is also commonly dilated and has a “cyst-like” appearance on prenatal

sonography.29 VUR is commonly seen in the lower moiety. Duplex kidney is more

common in females and is present bilaterally in about 15% to 20% of cases. The

suspicion of duplex kidney in the first trimester is rare, and the diagnosis is, however,

feasible when alerted by family history. The presence of two renal pelves in one kidney

on coronal view suggests the diagnosis.Figure 13.36: Coronal plane of the fetal abdomen, obtained with the

transabdominal linear probe, in a fetus with a left pelvic kidney diagnosed at 12

weeks of gestation (same fetus as in Fig. 13.35). Note the presence in A of a

left pelvic kidney (arrow) and a flat adrenal gland (asterisk). B: The same

figure as in A, with annotations to display both kidneys and adrenals. The

kidneys are encircled and the adrenal glands are highlighted in red. Note the

normal triangular shape of the adrenal on the right (R) side and the flat left (L)

adrenal. The left pelvic kidney is shown in the pelvis as opposed to the

abdominal location of the right kidney.Figure 13.37: Coronal planes of the fetal abdomen in two fetuses with

horseshoe kidneys (arrows) at 13 weeks of gestation. Because of the

increased echogenicity in the kidneys in the first trimester, the renal bridge

between the right and left kidney across the midline can be well appreciated.

The fetus in A had other anomalies and trisomy 18 was confirmed. Fetus in B

also had cystic hygroma and body edema (double headed arrow) and the

diagnosis of monosomy X was confirmed.

Bladder Exstrophy and Cloacal Abnormalities

Bladder exstrophy is a defect of the anterior lower abdominal wall, inferior to the

insertion of the umbilical cord, and involving the protrusion of the urinary bladder.

Typically, the umbilical cord inserts low on the abdominal wall, and the bladder

mucosa is eventrated directly below the umbilical cord. Bladder exstrophy occurs more

commonly in males than in females, and is associated with abnormalities in fetal gender

with bifid clitoris or penis or with epispadia. In addition, pelvic and pubic bones are

widened. Bladder exstrophy can be isolated or can be part of cloacal malformation, as

discussed in detail in Chapter 12. The diagnosis of isolated cases of bladder exstrophy

can be easily missed on ultrasound. As reported in a literature review of 10 cases,

typical clues to the presence of bladder exstrophy include a nonvisible fetal bladderduring the first trimester ultrasound examination, along with the presence of normal

kidneys and low umbilical cord insertion.30 In the presence of bladder exstrophy, axial

plane of the pelvis in color Doppler will show an absent bladder along with the

presence of a “mass of tissue,” resulting from bladder exteriorization. The presence of

other fluid-filled structures in the pelvis, including urachal remnant, may be misleading

in cases of bladder exstrophy.31 Figure 13.38A is a midsagittal plane of a normal fetus,

and Figure 13.38B is a fetus with bladder exstrophy showing the presence of a low

insertion of the umbilical cord along with abnormal tissue inferior to the cord insertion.

During the first trimester ultrasound, the diagnosis of bladder exstrophy can be easily

missed if imaging of the lower anterior wall of the abdomen and the bladder with the

surrounding umbilical arteries is not performed. Bladder exstrophy is a sporadic

anomaly, which could be part of syndromic conditions and other more complex

malformations, thus making fetal counseling difficult,30,31 especially in the first

trimester. We recommend a close follow-up ultrasound examination at 16 weeks of

gestation if the diagnosis of bladder exstrophy is suspected in the first trimester. This is

important to confirm the diagnosis and to exclude additional urogenital, gastrointestinal,

and other anomalies.

Figure 13.38: Midsagittal plane in a normal fetus (A) at 12 weeks of gestation

and in a fetus with bladder exstrophy (B) at 13 weeks of gestation. The bladder

could not be visualized in fetus B during the detailed ultrasound examination.

When compared with the normal fetus A, note the presence of a low abdominal

cord insertion (short arrow) in B. Also note the presence of irregular tissue

inferior to the cord insertion in B, which represents bladder exstrophy. Fetal

gender could not be well identified in B.

Cloacal abnormalities refer to a spectrum of anomalies where the gastrointestinal,

urinary, and genital tracts share a common cavity for discharge. Embryologically, a

cloaca persists beyond the fourth to sixth week of gestation when the partition of the

cloaca into the urogenital sinus and the rectum fails to occur. The diagnosis of cloacal

abnormalities is possible in the first trimester, especially in its severe forms. The

presence of a cystic structure in the mid- or lower abdomen in the first trimester should

alert for the possible presence of cloacal abnormalities, because the cystic structure

may represent a communication between the bladder and bowel (Figs. 12.44 to 12.46).Association of cloacal abnormalities with enlarged nuchal translucencies has been

reported.32 In its severe form, bladder exstrophy can be part of cloacal exstrophy, and

include an omphalocele, bladder exstrophy, imperforate anus, and spinal defects: a

constellation of malformations referred to as OEIS (see Chapter 12). The presence of

ambiguous genitalia is a common association.

Abnormal Genitalia

There are currently no comprehensive studies or reports on the diagnosis of abnormal

genitalia in the first trimester. As described earlier in this chapter, the reliable

assessment of the normal genitalia can be achieved from 12 weeks onward in optimal

imaging. It is, however, difficult to achieve a definitive diagnosis on any gender

malformation in the first trimester, with the exception of cloacal abnormalities. Once a

renal malformation is suspected in the first trimester, however, ultrasound assessment of

the genitalia should be performed because this may help in confirming the diagnosis.

For instance, PUV is typically found in males, whereas megacystis microcolon

peristalsis syndrome is found more commonly in females. The absence of one kidney, in

combination with a single umbilical artery and abnormal genitalia, may raise the

suspicion for a syndromic condition. Gender discrepancy between chorionic villous

sampling and ultrasound in a male fetus could suspect the presence of sexual reversal,

as in Smith–Lemli–Opitz syndrome, campomelic dysplasia, chodrodysplasia punctata,

and others. Figure 13.39 shows a case of a thickened nuchal translucency in a male

fetus with suspected aortic coarctation, where chorionic villous sampling revealed

Turner syndrome mosaic.

Abnormal Adrenal Gland

The adrenal gland appears as an anechoic structure between the kidney and diaphragm,

with an adrenal length about half the length of the kidney.5,18 In the second and third

trimester of pregnancy, the adrenal glands are commonly abnormal in association with

neuroblastoma or hemorrhage, conditions that are not existent in the first trimester. On

the other hand, a flat adrenal gland can be a marker for the presence of an empty renal

fossa (Figs. 13.35 and 13.36), in renal agenesis or a pelvic kidney. In addition, we

reported on enlarged adrenal glands5 in a fetus with congenital adrenal hyperplasia and

found the adrenals to be larger than the kidneys (Fig. 13.40). It is important to note that

most cases of congenital adrenal hyperplasia do not have significantly enlarged adrenal

glands and remain undetected in utero.Figure 13.39: Axial plane of the chest at the level of the four-chamber view (A),

the three-vessel-trachea view (B), and nuchal translucency (C) in a fetus at 12

weeks of gestation. Note the presence of ventricular (A) and great vessel (B)

disproportion, suggesting the diagnosis of an aortic coarctation. Also note in C

the presence of a thickened nuchal translucency of 4 mm (asterisk). The

combination of a thickened NT with left ventricular outflow obstruction suggests

the diagnosis of monosomy X. The fetal gender was male, however, as shown

in C (circle). The diagnosis of mosaic 46 XY and 45 XO was confirmed on

invasive testing. PA, pulmonary artery; LV, left ventricle; RV, right ventricle; Ao,

aorta.1.

2.

3.

4.

5.

6.

7.

8.

Figure 13.40: Parasagittal (A) and coronal (B) planes of the abdomen in a

fetus at 14 weeks of gestation with congenital adrenal hyperplasia (CAH). Note

the enlarged size of the adrenal glands bilaterally (arrows) and compare with

normal first trimester adrenal glands, shown in Figure 13.7. In the previous

pregnancy, the diagnosis of CAH was performed,