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Prenatal Hydronephrosis

Sergio Fefer, MDa, Pamela Ellsworth, MDb,T

a

Division of Urology, University of Massachusetts Memorial Hospital, 55 Lake Avenue North,Worcester, MA 01655, USA

bBrown University and University Urological Associates, Providence, RI 02905, USA

A 22-year-old pregnant woman presented to the obstetrics and gynecology

clinic for her first obstetric examination accompanied by her husband and her

5-year-old daughter. A prenatal ultrasound for dates was obtained, and it revealed

an 8-week embryo well implanted in the uterus. She returned for a repeat

ultrasound at 20 weeks. The fetus appeared appropriate size for gestational age.

The placenta was well developed, as was the cranium, and the thoracic-abdominal ratio was normal. The right kidney appeared normal, but the left

kidney was abnormal. The left renal pelvis was dilated and measured 20 mm. The

amniotic fluid volume was normal. A follow-up ultrasound obtained 6 weeks

later demonstrated that the left renal pelvis was 25 mm and the sex of the fetus

was male. The parents were referred to a pediatric urologist for prenatal con-

sultation. The pediatric urologist discussed the recommended postnatal evalua-

tion with the parents, which decreased their anxiety.

The use of prenatal ultrasound has increased significantly over the past

20 years. In 1980, prenatal ultrasound was performed in 33% of pregnancies,whereas prenatal ultrasound was performed in 78% of pregnancies in 1987. The

incidence of a significant structural abnormality detected by prenatal ultrasound

is 1% [1]. The rate of prenatal abnormalities detected by screening ultrasound

varies with the timing of fetal imaging, however. Detection rates increase when

ultrasound is performed at midtrimester compared with earlier scanning [24].

Abnormalities of the genitourinary tract rank second in frequency of structural

abnormalities on screening ultrasound. Approximately 50% of the structural

abnormalities involve the central nervous system, 20% involve the genitourinary

tract, 15% involve the gastrointestinal tract, and 8% involve the cardiopulmonary

0031-3955/06/$ see front matterD 2006 Elsevier Inc. All rights reserved.

doi:10.1016/j.pcl.2006.02.012 pediatric.theclinics.com

T Corresponding author.

E-mail address: [email protected] (P. Ellsworth).

Pediatr Clin N Am 53 (2006) 429447
http://dx.doi.org/10.1016/j.pcl.2006.02.012http://pediatric.theclinics.com/mailto:[email protected]:[email protected]://pediatric.theclinics.com/http://dx.doi.org/10.1016/j.pcl.2006.02.012http://-/?-http://-/?-

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system [5]. Hydronephrosis is the most common genitourinary tract anomaly

detected on prenatal ultrasound studies.

Not all cases of prenatally detected hydronephrosis are clinically significant.Several studies have assessed the threshold for diagnosing fetal hydronephrosis

associated with persistent renal anomalies [6,7]. In most of these studies,

persistent postnatal renal abnormalities are noted when the anteroposterior

diameter (APD) of the fetal renal pelvis measures N6 mm atb20 weeks, N8 mm at

20 to 30 weeks, and N10 mm atN30 weeks gestation. To further characterize the

dilatation of the collecting system and correlate fetal hydronephrosis with

postnatal clinical relevance, a grading scale was developed for fetuses older than

20 weeks gestation

Grade I: pelvic APD is 1 cm and the calyces are normal

Grade II: pelvic APD is 1 to 1.5 cm but the calyces remain normal

Grade III: pelvic APD is N1.5 cm and there is slight caliectasis

Grade IV: pelvic APD N1.5 cm with moderate caliectasis

Grade V: APD N1.5 cm with severe caliectasis and thinning of the renal cortex

(b2 mm thick) (Figs. 14) [8,9].

The grade of hydronephrosis has been demonstrated to correlate with the

potential for resolution of the hydronephrosis. Grade I hydronephrosis resolves inapproximately 50% of patients, whereas grades II, III, and IV hydronephrosis

resolve in 36%, 16%, and 3% of cases, respectively [10].

Fig. 1. Grade 1 hydronephrosis: renal pelvis is dilated without dilatation of the renal calices. (From

Shimada K, Kakizaki H, Kubota M, et al. Standard methodology for diagnosing dilatation of

the renal pelvis and ureter discovered in the fetus, neonate or infant. Int J Urol 2004;11(3):130;

with permission.)

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Although hydronephrosis may be a component of various congenital

syndromes, isolated unilateral dilatation of the collecting system is the most

frequent abnormality seen on prenatal ultrasound. Prenatal hydronephrosis is

associated with various conditions, which vary in severity and prognosis and

range from urethral atresia with complete urinary obstruction and fetal demise to

transient physiologic dilatation of the collecting system that resolves sponta-

neously without sequelae. In addition to an assessment of the kidneys, the

Fig. 2. Grade 2 hydronephrosis: dilation of the renal pelvis. Some of the calices are dilated.

(From Shimada K, Kakizaki H, Kubota M, et al. Standard methodology for diagnosing dilatation of

the renal pelvis and ureter discovered in the fetus, neonate or infant. Int J Urol 2004;11(3):131;

with permission.)

Fig. 3. Grade 3 hydronephrosis: dilatation of the renal pelvis. All of calices are dilated.

(From Shimada K, Kakizaki H, Kubota M, et al. Standard methodology for diagnosing dilatation

of the renal pelvis and ureter discovered in the fetus, neonate or infant. Int J Urol 2004;11(3):131;

with permission.)

prenatal hydronephrosis 431

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composition [12,13]. The amniotic fluid volume reflects renal function and

patency of the genitourinary tract. Oligohydramnios may have a significant

impact on fetal survival. Pulmonary hypoplasia is the most common cause for

mortality in neonates with obstructive uropathy. The most predictive factor inassessing the risk of pulmonary hypoplasia is the presence of mid-gestational

oligohydramnios. Nakayami and colleagues [14] noted that in neonates with

posterior urethral valves there is a 45% mortality rate, mostly because of pul-

monary insufficiency. Early prenatal detection of urinary tract malformations

associated with oligohydramnios affords the opportunity for prenatal intervention

in select cases. Currently, fetal treatment programs recommend treatment only for

fetuses at risk for neonatal death [15]. Before intervention for oligohydramnios

it is important to assess the likelihood of salvageable renal function and document

a normal karyotype. Currently, renal ultrasound and urine electrolytes are usedto determine the likelihood of salvageable renal function. Urine electrolyte values

associated with a good outcome include a urine sodium b100 mmol/L, a chloride

b90 mmol/L and osm b210 mOsm/L [16]. The sensitivity of the urine electrolytes

may be enhanced by sequential aspiration and analysis. Other new markers of

renal function include beta-2 microglobulin, alpha-microglobulin, and retinal

binding protein [16]. The vesicoamniotic shunt is the primary treatment modality

for severe oligohydramnios associated with bladder outlet obstruction. It is a

small, hollow catheter in which one end is placed into the bladder and the other

into the amniotic cavity, which allows fetal urine to drain into the amniotic space.Initial results with vesicoamniotic shunts were disappointing; there was a 4.6%

procedure-related mortality rate and overall survival rate of only 41% [17].

Refinements in technique and the use of antibiotics have improved the morbidity

associated with the procedure and increased postnatal survival rates to 67% [17].

Intrauterine follow-up of fetuses with unilateral hydronephrosis is controver-

sial. Although a dynamic, longitudinal evaluation of the urinary tract with serial

Table 1

Causes of antenatal hydronephrosis and ultrasound characteristics

Ipsilateral ureter Bladder UPJO Normal Normal

Vesicoureteral reflux Dilated or normal Dilated or normal

Ureterocele Dilated Dilated or normal

(cystic massureterocele)

Ectopic ureter Often dilated Normal

Posterior urethral valves Often dilated (bilateral) Thick wall, increased

postvoid residual

Multicystic kidney Normal Normal

Primary obstructive or nonrefluxing

nonobstructing mega-ureter

Dilated Normal

Urethral atresia Dilated (bilateral) Thick wall, not emptying

(oligohydramnios)

Retrocaval ureter Dilated proximal and

normal distal

Normal

Prune belly syndrome Dilated Dilated

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ultrasound is important in cases of bilateral hydronephrosis, the role of third

trimester ultrasound in cases of unilateral hydronephrosis is less clear. In the

setting of unilateral hydronephrosis, if the hydronephrosis increases in sub-sequent ultrasound studies, in utero intervention or early delivery still would not

be indicated.

Postnatal assessment

Physical examination of newborns with unilateral antenatal hydronephrosis is

usually normal. A palpable, transilluminating abdominal mass occasionally may

be present and is associated with cases of severe UPJO or multicystic kidneydisease. A distended bladder might be identified as a palpable mass in the

suprapubic area in infants and can lead to the diagnosis of bladder outlet ob-

struction by posterior urethral valves in boys or obstructing ectopic ureterocele in

girls. The observation of spontaneous voiding with normal urinary stream within

the first 24 hours of life does not rule out an obstructive process. On the contrary,

failure to void within the first 48 hours of life favors the diagnosis of obstructive

uropathy, such as posterior urethral valves or urethral atresia. Urethral atresia is

usually not compatible with life because of the associated severe oligohydram-

nios present in utero.Postnatal serum creatinine levels are rarely obtained with unilateral hydro-

nephrosis and a normal contralateral kidney but are indicated when there are

abnormalities of both kidneys. Interpretation of the serum creatinine obtained

during the first day or two of life is limited because the value reflects the mothers

creatinine. If the serum creatinine is elevated at the time of initial evaluation,

serial creatinine levels should be obtained until the levels normalize or plateau.

Newborns delivered at term should have serum creatinine levels at approximately

0.4 mg/dL at the end of their first week of life. A serum creatinine of N0.8 at

1 year of life is associated with an increased risk of renal insufficiency [18,19].

Postnatal management

Newborns with antenatal diagnosis of hydronephrosis should be started

on prophylactic antibiotics after birth until follow-up radiographic studies

are obtained. Traditionally, amoxicillin is used as the prophylactic antibiotic

of choice in newborns. At 8 weeks of life, when an infants liver is mature,

trimethoprim-sulfamethoxazole or nitrofurantoin may be used if continued pro-phylaxis is warranted.

All infants with prenatally detected hydronephrosis should undergo a postnatal

renal/bladder ultrasound study (Fig. 5). Concern has been raised regarding the

timing of the postnatal renal/bladder ultrasound. It was initially believed that in

the absence of suspicion of potential life-threatening anomalies (eg, posterior

urethral valves), a postnatal renal ultrasound should not be performed until after

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Prenatalhydroneph

rosis

Girls

Boys

VUR

NegativeVC

UG

UnilateralorBilateralHydro

Mildtomoderate

Continue

prophylaxis

RepeatrenalUS

Moderatetosevere

Prophylaxis

PostnatalUS

VCUG

VCUGand

USat1yr

Lasix

Mag3renalscan

Prophylaxis

Po

stnatalUS

VCUG

VUR

NegativeVCUG

M

ildtomoderate

RepeatrenalUS

Severe

LasixMag3Renalscan

at1month

RepeatUS

Ifhighgrade,considerDMSAto

assessfordysplasia

Considercircumcision

VCUGandUSat1yr

Fig.5.

Postnatalmanagementschemeforprenatalhydronephrosis.


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48 hours of life. The rationale for this decision was the premise that an initial low

glomerular filtration rate coupled with relative dehydration caused by poor

feeding could lead to oliguria during the first 48 hours of life and underestimatethe degree of renal dilatation in a partially obstructed system. Docimo and Silver

[20] reviewed the records of 101 neonates with prenatally detected hydro-

nephrosis who underwent sonography within 48 hours of birth. Thirty-three had

a normal postnatal study (either no or mild hydronephrosis) and documented

follow-up studies. None of the children had a significant obstructive renal lesion

within the first year of life, and 1 had an obstructive pattern on diuretic renog-

raphy at 18 months of age after previous studies were unremarkable. Wiener and

OHara [21] performed a prospective study that compared prenatal ultrasound

findings at 48 hours of birth to those at 7 to 10 days of life. The authors noted thatthe grade of hydronephrosis changed between the initial sonogram in the first

48 hours of life and the second sonogram at 7 to 10 days in most evaluable renal

units. In those renal units with significant uropathy, however, there was no sig-

nificant difference in the grade of hydronephrosis between the two ultrasounds.

Although it is ideal to obtain the postnatal renal ultrasound at approximately

7 days of life, in individuals in whom compliance or other factors may prevent

this, a renal ultrasound obtained at 48 hours of life is acceptable.

Postnatal persistence of prenatally diagnosed hydronephrosis requires further

evaluation. The Society for Fetal Urology developed a grading scale to assess theseverity of postnatal urinary tract dilatation (Table 2). The degree of dilatation of

the collecting system and thickness of renal parenchyma are the cornerstones of

this grading system. There is a strong correlation between the grade of hydro-

nephrosis and the likelihood of surgical intervention being required. Similar to

the prenatal scenario, ultrasound examination of the remainder of the genito-

urinary tract, including ureters, bladder, and urethra, is important in establishing

the final diagnosis.

The presence of persistent unilateral hydronephrosis on postnatal ultrasound

requires further evaluation to determine the cause (Fig. 5.) In these cases, pro-phylactic antibiotic are continued until further radiologic evaluation is completed.

A voiding cystourethrogram is obtained to evaluate for ipsilateral VUR and, in

boys, posterior urethral valves. Further evaluation with a furosemide 99mTc

mercaptoacetyltri-glycine (lasix Mag3) renal scan is determined by the grade of

hydronephrosis and the presence/absence of VUR. Infants with postnatal mild to

moderate hydronephrosis should undergo a repeat ultrasound in lieu of a diuretic

Table 2

Society for Fetal Urology grading system of congenital hydronephrosis

Grade Central renal complex Renal parenchyma

0 Intact Normal

1 Slight splitting of the pelvis Normal

2 Evident splitting of pelvis and calices Normal

3 Wide splitting of pelvis and calices Normal

4 Further splitting of pelvis and calices Reduced

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renal scan. In the setting of postnatal moderate to severe hydronephrosis, a lasix

Mag3 renal scan is obtained typically at 1 month of age when the kidneys are

more mature.Two parameters are evaluated on the lasix Mag3 renal scan: (1) the split renal

function and (2) the half time (tO), the time it takes for half of the radionuclide

to leave the renal collecting system. Normal differential renal function is believed

to be 45 to 50/55 to 50. If the renal function of the hydronephrotic kidney is

b40%, compromised function is present [22,23]. A normal half-time is less than

10 minutes, and a half-time that indicates some element of obstruction is more

than 20 minutes. The area between 10 and 20 minutes is an indeterminate region

and warrants continued observation. There are limitations in the assessment of

half-time, including the state of hydration, the renal function, the volume andcontractility of the renal pelvis, patient position, bladder filling, and timing and

dose of diuretic administration.

A combination of split renal function and half-time is often used to determine

if a significant obstruction is present. Careful review of the postnatal ultrasound

and the lasix Mag3 renal scan is important to assess the location of the obstruc-

tion. The absence of an ipsilateral dilated ureter confirms a UPJO, whereas

the presence of ipsilateral ureteral dilatation suggests a mega-ureter, obstructive

or nonobstructive.

The subsequent evaluation of an infant with prenatally detected hydro-nephrosis whose postnatal ultrasound is normal is controversial. The primary area

of controversy is the role of postnatal VCUG in this setting. Recent publications

showed that routine use of VCUG to evaluate all newborns with prenatal diag-

nosis of hydronephrosis resulted in detection of VUR in only 12% to 21% of the

cases [24,25]. Although VCUG is commonly performed, it is an invasive test that

exposes infants to ionizing radiation and carries the risk of new onset of urinary

tract infection (UTI) [2628]. In the setting of a normal postnatal ultrasound, the

pros and cons of a VCUG should be discussed with the family.

Several attempts have been made to identify infants with the highest chance ofhaving VUR by carefully evaluating the prenatal ultrasound, with the goal of

reducing unnecessary postnatal invasive testing. Herndon and colleagues [29]

noted that the prenatal ultrasound characteristics that support the presence of

VUR include bilateral mild to moderate renal pelvic dilation, dilatation of the

collecting system that increases with voiding during gestation, visualization of a

ureter, and family history of reflux.

Causes of prenatal hydronephrosis

Ureteropelvic junction obstruction

UPJO accounts for 44% to 65% of the cases of prenatal hydronephrosis [10].

UPJO occurs in 1 in 2000 live births, boys are more commonly affected, and 90%

of cases are unilateral [30]. The most common cause of UPJO in the pediatric

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population is an adynamic ureteral segment at the junction between the ureter and

the renal pelvis, the ureteropelvic junction. This nonfunctional ureteral segment

creates a resistance that compromises urine passage from the renal pelvis into theproximal ureter. Extrinsic compression of the proximal ureter by the presence of

accessory lower pole renal vessels may cause UPJO in children, but it is more

commonly seen in adults [31]. Rarely, hydronephrosis may be the result of in-

trinsic anomalies, such as ureteral valves or polyps or extrinsic bands.

Historically, a child with a UPJO presented with a palpable abdominal mass

or UTI during the first and second year of life or gastrointestinal complaints in

older children. In utero identification is currently the most common presenta-

tion of UPJO. Concerns have been raised that in utero identification and early

postnatal confirmation will lead to an increased number of surgical proceduresbeing performed in children with asymptomatic urinary tract dilatation. A

hospital-based study by Brown and colleagues [32] supported this concern.

Wiener and colleagues [33] examined the annual rate of pyeloplasty in the

population before the advent of maternal ultrasound and compared it to the rate

after the introduction of maternal ultrasound, however, and concluded that

maternal ultrasound did not lead to an overdiagnosis of UPJO but rather the

detection of the disease at an earlier age. This finding suggests that prenatally and

Fig. 6. Postnatal Lasix Mag 3 renal scan demonstrates decreased renal function. Percent renal function

at 2 minutes is 33.8% left and 66.2% right.

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postnatally detected hydronephrosis represents a continuous spectrum of the

same disease entity.

A corollary of early detection is the question of timing of intervention. Is itbetter to intervene earlier or observe and intervene when the obstruction is noted

to compromise renal function? With the advent of diuretic renography the initial

emphasis was placed on the drainage time (tO) and drainage curve. In the 1980s,

Ransley and colleagues [22] proposed that the emphasis should be placed on the

renal function instead of the drainage curve and half-time drainage (Figs. 6 and 7).

The critical value of renal function suggestive of obstruction is controversial.

Recommendations were made by several authors that hydronephrosis with

ipsilateral differential renal function more than 30% to 40% should be treated

conservatively with periodic renal ultrasound studies and diuretic renography[22,23]. Several authors have demonstrated that in most children with UPJO

conservative management is safe. Only 10% to 25% of children followed

conservatively ultimately require surgical intervention, and most children who

require surgical intervention do so within the first 2 years of life [22,34]. In

children in whom the hydronephrosis does not resolve during follow-up, it takes

approximately 30 months for maximal ultrasound improvement in the hydro-

nephrosis [34].

Fig. 7. Postnatal Lasix Mag 3 renal scan in same patient demonstrates abnormal drainage curve for

left kidney.

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In children without a significant obstruction, the optimal timing for subsequent

studies is not well established. The timing of studies often varies with the degree

of dilatation on ultrasound and the split renal function and half-time on renalscan. Dhillon [35] recommends earlier and more frequent isotope scans in neo-

nates with a severe degree of dilatation (APD N20 mm) or calyceal involvement

or infants with more than 40% renal function at 3 months of age whose dilata-

tion persists on subsequent renal ultrasounds. The duration and follow-up for

children with persistent hydronephrosis remains unclear and varies with the

degree of dilatation.

Surgical intervention

Currently, the presence of symptoms, declining renal function on renal scan,

and increasing hydronephrosis on ultrasound are clear indications for surgical

correction. A decrease in renal function of 10% or more on subsequent renal scan

is believed to indicate high-grade obstruction and warrants surgical intervention

[22,23]. A study performed by the Society of Fetal Urology in infants and

children with high-grade obstructive hydronephrosis concluded that children

b6 months of age with high-grade obstructive unilateral hydronephrosis with

good renal function were better served by pyeloplasty than observation [36].

Surgical correction of UPJO involves excision of the adynamic portion,

tailoring of the redundant renal pelvis, and reapproximation of the ureter in a

dependent fashion to the renal pelvis. This procedure is traditionally performed

through a retroperitoneal approach, either by an incision on the back (dorsal

lumbotomy) or, more commonly, a transverse incision on the lateral aspect of the

abdomen. More recently, pediatric urologists with advanced laparoscopic skills

have performed the procedure laparoscopically [37].

Vesicoureteral reflux

VUR is often believed to be a benign condition in the absence of UTIs. The

big bang theory of renal scarring suggests that first febrile UTI often may be a

cause of renal scarring. Uncircumcised infant boys have a higher risk of UTIs in

the first year of life than girls. Infant boys with prenatally detected VUR (hydro-

nephrosis on prenatal ultrasound) tend to have higher grades of VUR, which

may be associated with renal dysplasia [38]. In infants with prenatally detected

hydronephrosis, postnatal management with prophylaxis and subsequent VCUGallows for earlier detection of infants at greater risk for UTIs and possible

scarring. Unfortunately, postnatal renal ultrasound has little value in the diagnosis

of VUR. Postnatal ultrasound results are frequently normal in most cases of VUR

identified by prenatal ultrasound.

Some authors have argued that VUR detected in the context of a normal

postnatal ultrasound is a self-limiting condition that could be left alone. Others

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have demonstrated no correlation between the degree of prenatal or postnatal

grade of hydronephrosis and the grade of VUR. Of the children with prenatal

hydronephrosis in one study, there was no postnatal hydronephrosis in 27% ofthe grade 25 refluxing units [24]. One should consider performing a postnatal

VCUG to evaluate for reflux even in infants with a normal postnatal ultrasound,

particularly infants with prenatal ultrasound findings that suggested VUR [29].

Children with prenatally detected VUR are managed similarly to children with

UTI-related reflux. They are placed on antibiotic prophylaxis and followed with

sequential renal ultrasound and VCUG to assess renal growth and resolution of

VUR. The indications for surgical correction of prenatally detected VUR are the

same as those for UTI-related VUR, including breakthrough UTIs, persistence of

reflux, and poor compliance.

Posterior urethral valves

Posterior urethral valves represent a congenital valvular obstruction caused by

a mucosal membrane in the posterior urethra that results in different grades of

bladder outlet obstruction and proximal urinary tract dilatation. The incidence of

posterior urethral valves is generally accepted to be between 1 in 5000 and 1 in

8000 live male births [39]. Posterior urethral valves represents 3% to 9% of

all prenatally diagnosed cases of hydronephrosis [40,41]. Prenatal ultrasoundfindings that suggest posterior urethral valves include enlarged bladder, thickened

bladder wall, posterior urethral dilation, unilateral or bilateral hydronephrosis,

increased renal echogenicity, and oligohydramnios (Fig. 8) [42]. Such ultrasound

anomalies suggestbut are not definitive forposterior urethral valves. El

Ghoneimi and colleagues [43] noted that only 53% of male fetuses with mega-

cystis and bilateral hydronephrosis had posterior urethral valves.

The detection of posterior urethral valves after 24 weeks gestation is asso-

ciated with a better prognosis than cases detected before 24 weeks [42]. Second

trimester findings that portend a poor postnatal outcome include moderate orsevere upper tract dilation, renal pelvic APD N10 mm, and increased echogenicity

or cystic changes in the renal parenchyma.

In male infants with oligohydramnios and salvageable renal function, early

detection and management via placement of a vesicoamniotic shunt may enhance

survival by improving pulmonary function. Currently limited data are available to

demonstrate that prenatal detection and intervention with vesicoamniotic shunt in

high-risk neonates improve renal function. Early identification and intervention

decrease the complications of postnatal septicemia and uremia, however.

Male newborns with severe bilateral hydronephrosis and oligohydramniosrequire emergent postnatal medical management for correction of pulmonary

dysfunction and electrolyte disturbances. A catheter should be placed immedi-

ately and urine output should be monitored. Once stabilized, a newborn should

undergo a VCUG to confirm the presence of posterior urethral valves. If valves

are detected, transurethral surgical ablation of the posterior urethral valves is

performed. Follow-up imaging is required to ensure that the obstruction is

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relieved and to evaluate bladder emptying and upper tract dilatation. Further

evaluation and management of infants with posterior urethral valves are dictated

by their renal function, bladder function, and the presence/absence of other

anomalies, such as high-grade reflux or a nonfunctioning kidney. A nadir serum

creatinine of N0.8 mg/dL at 1 year of age indicates a long-term risk of renal

insufficiency [18,19].

Ureterocele

A ureterocele is a cystic dilatation of the distal portion of the ureter. Although

most ureteroceles present in girls (female:male ratio of 4:1) and in association

with ureteral duplication (80%), multiple anatomic variants and clinical pre-

sentations have been reported [44,45].

More frequently the ureterocele is associated with obstruction of the upper

pole moiety of a duplicated collecting system, and the postnatal ultrasound dem-onstrates unilateral upper pole hydroureteronephrosis. The upper pole moiety is

often abnormal in appearance with little, if any, parenchyma. With large ure-

teroceles, bladder outlet obstruction may be present and bilateral hydronephrosis

may be seen on ultrasound.

Historically, the diagnosis of a ureterocele was made during the evaluation

of a UTI in infancy and early childhood. More increasingly, ureteroceles are

Fig. 8. Prenatal ultrasound appearance of severe posterior urethral valves in a male fetus. The blad-

der is moderately distended and there is severe dilatation of the collecting system of both kid-

neys with normal appearing renal parenchyma. (From Peters CA. Perinatal urology. In: Walsh OC,

Retik AB, Vaughn ED, et al, editors. Campbells urology. 8th edition. Philadelphia: WB Saunders;

2002. p. 1787.)

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being detected on prenatal ultrasound evaluation. Ureteroceles have been de-

tected on prenatal ultrasounds as early as 17 weeks gestation. Kitagawa and

colleagues [41] were able to identify 62.5% of ureteroceles by 20 weeks ges-tation and the remainder at 21 to 23 weeks gestation. Although prenatal

detection of ureteroceles does not routinely alter the course of a pregnancy, in rare

cases in utero intervention may be indicated for ureteroceles associated with

bladder outlet obstruction and oligohydramnios [4648].

When a ureterocele is identified on prenatal ultrasound, serial ultrasound

studies are obtained to follow the amniotic fluid volume, bladder volume, degree

of hydronephrosis, and echogenicity of the kidneys. Current indication for in

utero intervention includes progressive bladder outlet obstruction with increasing

megacystis and oligohydramnios. In utero interventions are designed to decom-press the ureterocele and restore bladder emptying and amniotic fluid volume

[4648].

The impact of the prenatal diagnosis of ureterocele on the ultimate renal

function is controversial. A few series support better upper pole renal function

with prenatal diagnosis, yet others indicate that there is no difference in function

of the obstructed upper pole [4951]. Although controversy remains as to the

impact of prenatal ultrasound on the function of the affected upper pole moiety, it

is clear that prenatal detection of ureteroceles does impact the morbidity asso-

ciated with ureterocele [4951]. Prenatal diagnosis has allowed for early insti-tution of prophylactic antibiotics and has led to a decreased incidence of UTIs

from 70% to 80% historically to 3% to 15% currently [5153]. Upadhyay and

colleagues [53] demonstrated that prenatal diagnosis of ureterocele is associated

with a decreased rate of secondary procedures independent of the type of ure-

terocele. In infants who underwent partial nephrectomy there was a 16% reopera-

tion rate in the prenatally detected group compared with a 38% reoperation rate in

the postnatally detected group.

Mega-ureter

Mega-ureter is a term applied to the presence of ureteral diameter of more than

1 cm. Primary mega-ureter occurs three to four times more often in boys and is

two to three times more common on the left side [54]. Currently, because of the

widespread use of maternal screening ultrasound, most cases of mega-ureter are

diagnosed prenatally. Postnatal ultrasound, VCUG, and renal scan are helpful to

confirm the cause of the mega-ureter. Mega-ureter may be classified as primary or

secondary and as refluxing, obstructive (defined by lasix Mag 3 renal scan),refluxing obstructive, or nonrefluxing nonobstructive mega-ureter [55].

In the absence of documented obstruction, mega-ureters are followed con-

servatively with periodic radiologic evaluations and antibiotic prophylaxis until

the dilatation is deemed stable or resolved. Surgical management involves ex-

cision of the obstructive distal segment, tapering of the distal ureter (if needed),

and ureteral reimplantation.

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Ectopic ureter

Ectopic ureters are associated with ipsilateral hydronephrosis and ureteraldilation on prenatal and postnatal ultrasound. A dilated ureter is often seen

posterior to the bladder on pelvic ultrasound. As with ureteroceles, ectopic ureters

are often associated with the upper pole of a duplex kidney (80%) and poor upper

pole function [56]. Ectopic ureters may have various abnormal insertions, the site

varying with the childs sex. In girls, the ectopic ureter may insert distally to the

bladder neck or into the vagina, which leads to incontinence [57]. In boys, the

most common site of insertion is the posterior urethra. Prenatal detection leads

to early identification and management decreasing the morbidity associated with

ectopic ureters. Surgical intervention is indicated for ectopic ureters. The pro-cedure varies with the renal function and may involve excision of a non-

functioning upper pole or ureteral reimplantation or ureteroureterostomy.

Multicystic dysplastic kidney

A multicystic dysplastic kidney may be confused with a severe UPJO. Careful

review of the renal ultrasound and assessment of renal function differentiate

between the two. On ultrasound, the multicystic dysplastic kidney demonstrates acollecting of renal cysts of varying size with no larger central or medial cyst

(Fig. 9). Renal functional studies demonstrate b10% function of the multicystic

dysplastic kidney. They are more common on the left side, and contralateral

anomalies include UPJO (3%12%) and VUR (18%43%) [58]. A VCUG is

Fig. 9. Multicystic dysplastic kidney with multiple, variable-sized cysts without a central dominant

cyst. (From Peters CA. Perinatal urology. In: Walsh OC, Retik AB, Vaughn ED, et al, editors.

Campbells urology. 8th edition. Philadelphia: WB Saunders; 2002. p. 1787.)

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needed to rule out contralateral VUR. Management of multicystic dysplastic

kidneys is conservative, with periodic ultrasound performed because they tend to

involute. Observation is indicated until they are no longer visible because of rarereported cases of Wilms tumor arising in multicystic dysplastic kidneys. Indi-

cations for removal include increasing size, respiratory compromise, or suspicion

of Wilms tumor.

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