The Fetal Genitourinary System

. If the kidneys fail to ascend into the normal position, the result is an

ectopic kidney (renal ectopica), most often located within the pelvis (pelvic kidney)

The most common renal anomaly is the

duplex collecting system, also referred to as a duplicated, duplex, or double collecting system

duplex collecting system consists of

two separate collecting systems, divided into what is termed an upper pole moiety and a lower pole moiety.

Horseshoe kidneys are kidneys that are attached at their

lower poles.

Initially , the bladder is continuous with the allantois, although eventually this channel closes and develops into a fibrous cord referred to as the

urachus

the urachus is located between the

apex of the bladder and the umbilicus.

The kidneys can be sonographically identified as early as

11 weeks with endovaginal imaging and by 12 weeks with transabdominal imaging

The fetal bladder can be seen as early as

12 weeks and should always be seen by 15 weeks and beyond

It is important to note that the fetal urinary bladder normally fills and empties once in every

30 to 45 minutes

Sonographic image of kidneys

Sonographic image of bladder

Sonographic image of adrenal gland

VACTERL stands for

vertebral anomalies, anal atresia, cardiac anomalies, tracheoesophageal fistula or esophageal atresia, renal anomalies, and limb anomalies; Patients are considered to have this association if three of the organ systems listed have abnormalities

Renal abnormalities are the most frequent cause of

oligohydramnios (after 9 weeks)

In circumstances in which the fetus has a renal abnormality, specifically those that are linked with bilateral renal agenesis, inadequately functioning kidneys, or obstruction of the urinary tract, oligohydramnios will be present, and, in some cases,

anhydramnios may occur

The most worrisome consequence of oligohydramnios is

pulmonary hypoplasia, or underdevelopment of the lungs.

Failure of a kidney to form is referred to as

renal agenesis

Bilateral renal agenesis, which results in

Potter syndrome or Potter sequence, is a fatal condition

Features of Potter syndrome or Potter sequence

Bilateral renal agenesis

Abnormal facial features (Potter facies)

Pulmonary hypoplasia (small chest)

Limb abnormalities (e.g., clubfeet)

Intrauterine growth restriction

Low-set ears

Oligohydramnios

Potter sequence is caused by any condition in which there is a significant lack of

amniotic fluid around the fetus as it develops

. Though bilateral renal agenesis can cause the typical Potter syndrome features, other conditions, such as an

obstructive defect of the urinary tract or amnion rupture, can cause the same issues.

Bilateral renal agenesis may be seen in conjunction with

sirenomelia and various cardiovascular malformations.

In the presence of unilateral renal agenesis, the contralateral kidney will enlarge, a condition known as

compensatory hypertrophy.

Sonographic Findings of Bilateral Renal Agenesis

Absent kidneys

Absent urinary bladder

Severe oligohydramnios or anhydramnios

Bilateral lying-down adrenal signs

Undetectable renal artery branches with color Doppler (bilateral)

Sonographic Findings of Unilateral Renal Agenesis

Absent kidney

Compensatory hypertrophy of the contralateral kidney

Visible urinary bladder

Normal amniotic fluid volume

Unilateral lying-down adrenal sign

Undetectable renal artery branch with color Doppler (unilateral)

Most often, with unilateral renal agenesis, there is an

average amount of amniotic fluid, and the prognosis is good.

There are several distinct categories of fetal renal cystic disease that were formerly described by Potter

autosomal recessive polycystic kidney disease (ARPKD), autosomal dominant polycystic kidney disease (ADPKD), multicystic dysplastic kidney (MCDK) disease, and obstructive cystic dysplasia.

In order for an autosomal recessive disease to be passed to the fetus, both parents must be carriers of the disease. Each offspring of parents, who are both carriers of an autosomal recessive disorder, has a

25% chance of being affected and a 50% chance of being a carrier.

In the case of an autosomal dominant disease, at least one of the parents has to be the carrier of the disease, and the gene must be dominant. That means, the dominant gene is capable of overriding the normal gene from the parent who is not a carrier. Each offspring of a parent who is a carrier of an autosomal dominant disease has a

50% chance of receiving the gene from their parents

ARPKD may also be referred to as

autosomal recessive polycystic renal disease or infantile polycystic kidney disease

One condition associated with ARPKD is

Meckel–Gruber syndrome, which is a fatal disorder that includes renal cystic disease, occipital encephalocele, and polydactyly

. Fetuses with trisomy 13 and trisomy 18 may also have

polycystic kidney disease

It is significant to appreciate the differences in the sonographic appearance of ARPKD and MCDK disease. Cysts are typically not identifiable in

ARPKD but are evident with MCDK (multicystic dysplastic kidney)

Sonographic Findings of Autosomal Recessive (Infantile) Polycystic Kidney Disease (ARPKD)

Bilateral, enlarged echogenic kidneys

Absent urinary bladder

Oligohydramnios

ADPKD may also be referred to as

autosomal dominant polycystic renal disease

If the kidneys do appear enlarged and echogenic, a distinguishing difference between the two diseases is that in the fetus with ADPKD, the urinary bladder is

often present and there is a normal amniotic fluid volume, whereas with ARPKD, the bladder is absent and there is oligohydramnios

Adult renal cystic disease is also associated with the development of

cysts within the liver, pancreas, and spleen (around 4th-5th decade of life)

Sonographic Findings of Autosomal Dominant (Adult) Polycystic Kidney Disease (ADPKD)

Normal-appearing or bilateral, enlarged echogenic kidneys

Visible urinary bladder

Normal amniotic fluid volume

Cysts often do not manifest until approximately the fifth decade of life

Multicystic dysplastic renal disease may also be referred to as

multicystic dysplastic kidney (MCDK) disease and multicystic renal dysplasia.

MCDK disease is thought to be caused by an

early, first-trimester obstruction of the ureter

There is typically no normal functioning renal tissue present in the kidney affected by MCDK disease. Therefore, MCDK disease is

fatal if bilateral (in most cases, it is unilateral)

Fetuses with MCDK disease can also have additional related anomalies, such as abnormalities of the

gastrointestinal tract and central nervous system, limb anomalies, and further renal abnormalities.

Sonographic Findings of Bilateral Multicystic Dysplastic Renal Disease

Bilateral, smooth-walled, noncommunicating cysts of varying sizes located within the renal fossae

Absent urinary bladder

Oligohydramnios

Sonographic Findings of Unilateral Multicystic Dysplastic Renal Disease

Unilateral, smooth-walled, noncommunicating cysts of varying sizes located within the renal fossae

Compensatory hypertrophy of the contralateral kidney

Visible urinary bladder

Normal amniotic fluid volume

Obstructive cystic dysplasia, like MCDK disease, is caused by an

early renal obstruction. It can be unilateral or bilateral

A ureterocele, or a severe bladder outlet obstruction, early in gestation, can lead to

bilateral obstructive cystic dysplasia, in which case oligohydramnios will be present.

Unilateral obstructive cystic dysplasia is most often caused by a

pelviureteral junction or vesicoureteral junction obstruction

. Bilateral cystic dysplasia may be associated with urethral atresia or

posterior urethral valves

Sonographic Findings of Bilateral Obstructive Cystic Dysplasia

Small, echogenic kidneys

Peripheral renal cysts

Bilateral hydronephrosis

Thick-walled urinary bladder

Oligohydramnios

An obstruction of the fetal urinary tract can lead to distension of the

urethra, bladder, ureters, and renal collecting system, depending upon the level of obstruction

Urine is produced by the kidney; exits the kidney by means of the

renal pelvis; travels down the ureter, into the bladder; and exits the body via the urethra

if there is an obstruction at the region where the ureter meets the bladder, the ureterovesical junction (UVJ),

then those structures that are positioned proximal to the obstruction will be dilated ( entire ureter, the renal pelvis, and the renal calices will be eventually dilated and filled with urine.)

Conversely, if the obstruction level lies at the point at which the renal pelvis meets the ureter, the ureteropelvic junction (UPJ), t

then the ipsilateral renal pelvis and renal calices will be dilated, whereas the ureter and bladder will most likely remain normal, provided that contralateral urine flow is not obstructed in any way

what is the most common fetal abnormality noted during an obstetric sonogram

Hydronephrosis

Hydronephrosis, or pelvocaliectasis, may be described as

pelviectasis (pyelectasis) or caliectasis, depending on which part of the collecting system is dilated

Enlargement of the bladder is called

megacystis

whereas dilation of the ureter may be referred to as

megaureter or hydroureter.

Fetal pelviectasis, or dilation of the renal pelvis, can be established and measured with sonography by taking a

renal pelvic diameter

The measurement of the renal pelvis is made in the anteroposterior plane and should not exceed

7 mm before 20 weeks’ or 10 mm after 20 weeks’ gestation

what are the three most common areas where obstruction occurs.

The UPJ, the UVJ, and the urethra

It is also important to note that less common causes of hydronephrosis in the fetus include

ureterocele, ectopic ureter, vesicoureteral reflux, and urethral atresia.

UreteroPelvic junction obstruction, or UPJ obstruction, is the most common cause of

hydronephrosis in the neonate and the most common form of fetal renal obstruction (located at junction of renal pelvis and renal calices)

UPJ is usually

unilateral and more common in males

Sonographic Findings of UreteroPelvic Junction Obstruction

Hydronephrosis (dilated renal pelvis and calices)

Normal ureters (nonvisualization)

Normal bladder

A bladder outlet obstruction describes the condition in which there is a

blockage of the flow of urine out of the urinary bladder.

posterior urethral valves are a common cause of

bladder outlet obstructions in male fetuses.

Sonographic Findings of Posterior Urethral Valves

“Keyhole” sign (dilated bladder and urethra)

Bilateral hydroureter

Bilateral hydronephrosis

Oligohydramnios

Thickened bladder wall

Prune belly syndrome (most seen in males) is typically caused by

megacystis, a massively dilated urinary bladder.

Sonographic Findings of Prune Belly Syndrome

Dilated bladder and, possibly, urethra (“keyhole” sign)

Absent abdominal musculature

Undescended testis

Urinary tract abnormalities (megacystis and hydronephrosis)

UreteroVesical junction obstruction, or UVJ obstruction, is the least

common cause of hydronephrosis in the fetus.

Sonographic Findings of Ureterovesical Junction Obstruction

Hydronephrosis

Dilated ureter

Normal bladder

Normal amniotic fluid (if unilateral)

Bladder exstrophy is an anomaly wherein the bladder is

located outside of the fetal pelvis.

After an extended amount of investigation, nonvisualization of the bladder in the presence of a normal amniotic fluid volume and normal kidneys should warrant a search for

bladder exstrophy

The cloaca is the embryonic structure that develops into the

rectum and urogenital sinus

With cloacal exstrophy, also referred to OEIS complex

there is an Omphalocele, bladder Exstrophy, Imperforate anus, and Spina bifida.

Sonographic Findings of Bladder Exstrophy

Lower abdominal wall mass inferior to the umbilicus

Absent urinary bladder

Normal kidneys

The most common solid fetal renal mass is the

mesoblastic nephroma (a hamartoma of the kidney. )

Sonographic Findings of The Mesoblastic Nephroma

Solid, homogeneous mass within the renal fossa and may completely replace the kidney.

Ambiguous genitalia is a birth defect in which the

sex of the fetus cannot be determined.

Findings of abnormal external genitalia in the male are

micropenis, hypospadias (opening on underside), hypospadias with chordee ((curvature of penis)), epispadias (opening on topside), and undescended testicles.

The most common female finding is

clitoromegaly

Fetal ovarian cysts may be noted in the fetal pelvis, secondary to

maternal hormone stimulation. These cysts are most often benign and resolve spontaneously, although if they continue to grow, they can lead to hemorrhage and, possibly, ovarian torsion.

The most common malignant adrenal pediatric tumor is the

neuroblastoma