overview of fetal hydronephrosis -...

Official reprint from UpToDatewww.uptodate.com ©2017 UpToDate

Overview of fetal hydronephrosis

Author: Laurence S Baskin, MD, FAAP

Section Editors: Tej K Mattoo, MD, DCH, FRCP, Louise Wilkins-Haug, MD, PhD, Duncan Wilcox, MD

Deputy Editor: Melanie S Kim, MD

All topics are updated as new evidence becomes available and our peer review process is complete.

Literature review current through: May 2017. | This topic last updated: Apr 25, 2017.

INTRODUCTION — Fetal hydronephrosis (dilation of the renal pelvis with or without dilation of the renal calyces) is a common finding on antenatal ultrasound [1,2]. In most cases, renal pelvic dilation is a transient physiologic state, however, congenital anomalies of the kidney and urinary tract (CAKUT) can present with fetal hydronephrosis due to urinary tract obstruction and vesicoureteral reflux (VUR). These conditions may be associated with impaired renal development and/or cause renal injury.

Nevertheless, the majority of cases of fetal hydronephrosis are not clinically significant, and therefore excessive concern may lead to unnecessary testing of the newborn infant and anxiety for parents and health care providers. The goal of prenatal management is to detect those cases of fetal hydronephrosis that may adversely affect the health of the infant and require antenatal and postnatal evaluation, timely referral to a pediatric urologist if required, and possible intervention to minimize adverse outcomes, while limiting testing in those cases that are due to a benign, transient condition.

The definition, etiology, and management of fetal hydronephrosis are reviewed here. Postnatal evaluation of fetal hydronephrosis and specific urologic conditions that may present as fetal hydronephrosis are discussed separately. (See "Postnatal management of fetal hydronephrosis" and "Congenital ureteropelvic junction obstruction" and "Primary megaureter in infants and children" and "Ectopic ureter" and "Clinical presentation and diagnosis of posterior urethral valves", section on 'Prenatal' and "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux".)

DEFINITION AND GRADING — Several systems have been developed to diagnose and grade the severity of fetal hydronephrosis [3]. There is no consensus on the most appropriate grading criteria for the diagnosis of fetal hydronephrosis [4]. In general, the likelihood of having a significant renal anomaly correlates with the severity of hydronephrosis.

Scoring systems differ based upon the fetal ultrasound criteria used and include:

Renal pelvic diameter (RPD) — The most generally accepted method to define and grade fetal hydronephrosis is measurement of the maximum anteroposterior diameter of the renal pelvis (APPD) in the transverse plane, also referred to as RPD [5]. Fetal hydronephrosis is graded according to the RPD during the second and/or third trimester of pregnancy. RPD is a measure of collecting system dilation and does not reflect the extent of hydronephrosis and parenchymal changes, such as increased echogenicity, thinning, or caliectasis. Varying the minimal RPD threshold for normal can significantly alter the positive predictive value of RPD as a measure of postnatal pathology. Lower cutoffs will be more sensitive in detecting postnatal pathology; however, the trade-off is in higher false-positive rates [6].

Several studies have established normative values for fetal renal size based upon gestational age (GA) [7-9]. However, there remains a lack of consensus on the threshold RPD that defines clinically significant fetal hydronephrosis, which necessitates postnatal follow-up and has a high likelihood for renal pathology:

Society of Fetal Urology (SFU) — The SFU developed criteria for the diagnosis and grading of fetal hydronephrosis based upon the degree of pelvic dilation, number of calyces seen, and the presence and severity of parenchymal atrophy (image 1) [20].

Urinary tract dilation (UTD) classification system — A multidisciplinary panel consisting of radiologists, nephrologists, and urologists has proposed a classification system that applies to UTD that presents either antenatally or postnatally (figure 1). It is based on six ultrasound findings (anterior and posterior RPD, calyceal dilation, renal parenchymal thickness, renal parenchymal appearance, bladder abnormalities, and urologic abnormalities) [21]. It is stratified based on GA and whether the detection is antenatal or postnatal. However, further evaluation is needed to establish the clinical accuracy and utility of this system. In the UTD system, the initial classification is based on antenatal and postnatal presentation (A versus P) [21]. It is based on assessing the six ultrasound features by transverse and sagittal views (anterior and posterior RPD,

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Renal pelvic diameter (RPD)●

Society of Fetal Urology (SFU) criteria●

Urinary tract dilation (UTD) classification system●

Most experts in the field use a value above 4 to 5 mm as the lowest cutoff for fetal hydronephrosis in the second trimester. GA, maternal hydronephrosis, maternal hydration, and the degree of bladder distention may affect the RPD [9-12].

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Mild renal pelvic dilation, also referred to as pyelectasia, is defined as an RPD of ≥4 to 10 mm in the second trimester [5,8,13,14]. Although most cases of mild renal pelvic dilation will resolve and not have a clinical impact on neonatal renal development, there are reports of persistent cases that require postnatal intervention [15-18].

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In general, RPD >10 mm in the second trimester is associated with an increased risk of significant congenital anomalies of the kidney and urinary tract (CAKUT) [5,8,13,16]. Fetuses with RPD >15 mm during the third trimester are at the greatest risk for CAKUT [5,8,13,16,19]. (See 'Congenital anomalies of the kidney and urinary tract (CAKUT)' below.)

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Grade 0 − Normal examination with no dilation of the renal pelvis●

Grade I − Mild dilation of the renal pelvis only (image 2)●

Grade II − Moderate dilation of the renal pelvis including a few calyces●

Grade III − Dilation of the renal pelvis with visualization of all the calyces, which are uniformly dilated, and normal renal parenchyma●

Grade IV − Similar appearance of the renal pelvis and calyces as grade III, plus thinning of the renal parenchyma (image 3)●

calyceal dilation, renal parenchymal thickness, renal parenchymal appearance, bladder abnormalities, and urologic abnormalities). The severity of findings is denoted by a numerical system (1 through 3, with 3 being the most severe grade) with grading based on the most severe finding. Because it is more challenging to visualize abnormalities in the fetus, there are only three antenatal categories (normal, A1 [mild abnormality], and A2-3 [more severe finding]) compared with four postnatal categories (normal, P1 [mild], P2 [moderate], and P3 [severe]) (figure 1).

EPIDEMIOLOGY — Hydronephrosis occurs approximately twice as often in males as in females. It is bilateral in 20 to 40 percent of cases [22]. The reported incidence of fetal hydronephrosis ranges from 0.6 to 4.5 percent of pregnancies. Differences in reported data may be due to different criteria used to define the disorder and the level of attention to the urinary system by the ultrasonographer [15,23-27].

ETIOLOGY — Fetal hydronephrosis may develop secondary to transient dilation of the collecting system, upper/lower urinary tract obstructive uropathy, and nonobstructive processes such as vesicoureteral reflux (VUR), megaureters, and prune-belly syndrome. The most common causes are transient hydronephrosis, ureteropelvic junction obstruction (UPJO), and VUR.

Transient hydronephrosis — Transient hydronephrosis is seen in 41 to 88 percent of cases and may be related to a transient narrowing of the ureteropelvic junction early in development that resolves as the fetus matures. Mild hydronephrosis with renal pelvic diameter (RPD) <6 mm in the second trimester or <8 mm in the third trimester is usually associated with transient hydronephrosis. However, the incidence is lower when all cases with RPD <10 to 12 mm are included [6].

Congenital anomalies of the kidney and urinary tract (CAKUT) — In a meta-analysis of 1678 infants diagnosed with fetal hydronephrosis, postnatal evaluation identified CAKUT as the underlying cause of fetal hydronephrosis in one-third of the patients [16]. UPJO (figure 2) was the most common diagnosis and increased in frequency with the severity of hydronephrosis. In contrast, VUR, the second most common diagnosis, was not associated with the severity of fetal hydronephrosis. However, moderate to severe reflux (grades III through V) appears to be associated with a greater degree of renal pelvic dilation (RPD >10 mm), both in utero and postnatally (figure 3) [28]. (See "Congenital ureteropelvic junction obstruction", section on 'Fetal and neonatal' and "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux".)

Other less common causes of fetal hydronephrosis due to CAKUT include:

Severity of hydronephrosis — The likelihood that an infant postnatally will have a significant CAKUT increases with the severity of persistent fetal hydronephrosis [16,29,30]. However, no criteria have been identified that can identify all neonates with significant pathology and exclude those infants with transient or physiologic hydronephrosis. Although a low threshold (eg, RPD >4 mm) in the second trimester will have a greater sensitivity of detecting infants with CAKUT, it would also include a large number of patients without renal disease who would undergo unnecessary testing. (See 'Definition and grading' above.)

The higher risk for CAKUT and postnatal surgical intervention with increasing severity of fetal hydronephrosis is demonstrated by the following:

In a meta-analysis that included 17 studies, fetal hydronephrosis was identified in 1678 fetuses of 104,572 women (1.6 percent) [16]. However, criteria for the diagnosis of hydronephrosis differed among the included studies.

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In one prospective Belgian study of 5643 unselected women, mild fetal hydronephrosis, defined as RPD ≥4 mm, was detected by ultrasonography during the second trimester in 4.5 percent of pregnancies [15].

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Megaureter (figure 4) (see "Primary megaureter in infants and children")●

Multicystic dysplastic kidney (MCDK) (see "Renal cystic diseases in children", section on 'Multicystic dysplastic kidney' and "Prenatal sonographic diagnosis of cystic renal disease", section on 'Multicystic dysplastic kidney')

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Ureterocele (image 4 and figure 5) (see "Ureterocele")●

Posterior urethral valves (PUV) (image 5) (see "Clinical presentation and diagnosis of posterior urethral valves")●

Ectopic ureter (see "Ectopic ureter")●

Prune-belly syndrome (see "Prune-belly syndrome")●

Urachal cyst●

Duplex collecting system (image 6)●

Urethral atresia●

In the previously mentioned meta-analysis of 1678 infants from 17 studies, the following incidence of renal/urinary tract pathology were noted based on fetal RPD measurements [16]:

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Mild hydronephrosis (≤7 mm in the second trimester and/or ≤9 mm in the third trimester) − 12 percent•

Moderate hydronephrosis (7 to 10 mm in the second trimester and/or 9 to 15 mm in the third trimester) − 45 percent•

Severe hydronephrosis (>10 mm in the second trimester and/or >15 mm in the third trimester) (image 3 and image 7) − 88 percent•

In a subsequently published review of single-center studies, prenatal resolution was noted in one-quarter of the 1034 cases [31]. Postnatal longitudinal evaluation for 440 of the remaining 742 cases demonstrated at the initial postnatal renal ultrasounds (mean age of 3.5 months) some degree of dilation in 80, 88, and 95 percent of mild, moderate, and severe cases of fetal hydronephrosis, respectively. At last follow-up (mean age 20.6 months), hydronephrosis persisted in 10, 25, and 72 percent of patients with mild, moderate, and severe fetal hydronephrosis, respectively. The incidence and causes of hydronephrosis in patients who underwent surgical intervention based on the severity of fetal hydronephrosis were as follows:

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Mild hydronephrosis – Surgical intervention performed in 26 of 267 cases (10 percent) for VUR (n = 14), UPJO (n = 7), PUV (n = 2), and 1 case each of cloaca, neurogenic bladder, and ectopic ureterocele.

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Timing and repeat ultrasound testing — The timing of prenatal ultrasonography is important for optimal detection of CAKUT. Ultrasonography performed before the 18 to 24 week of gestation can fail to detect significant disease [32,33]. Studies performed in the third trimester are more helpful in predicting postnatal outcome than screening earlier in the pregnancy [32,34-36].

However, fetal hydronephrosis is most commonly detected during routine fetal ultrasonography, which typically occurs in the second trimester (18 to 22 weeks gestation). We repeat testing for fetuses with hydronephrosis detected by ultrasound in the second trimester, as data from several studies demonstrate the utility of a repeat scan in the third trimester (28 to 34 weeks gestation) to identify those fetuses at risk for CAKUT and who may require postnatal intervention.

Down syndrome — Mild hydronephrosis is a common finding in fetuses with Down syndrome. Studies that defined hydronephrosis as RPD ≥4 mm in the second trimester demonstrated hydronephrosis is greater in Down syndrome compared with normal control fetuses (18 versus 0 to 3 percent, respectively) [26,39,40].

The finding of mild hydronephrosis should prompt a detailed assessment of fetal anatomy to identify other congenital anomalies. When pyelectasis is identified in an otherwise normal second trimester fetus and no previous maternal plasma or serum screening tests for trisomy 21 have been performed, the mother can be offered a cell-free DNA test to screen for trisomy 21. A normal result indicates a very low risk of an affected fetus and invasive diagnostic testing is typically avoided in these cases (see "Prenatal screening for common aneuploidies using cell-free DNA", section on 'Secondary screening'). A serum analyte test instead of a cell free DNA test is a reasonable alternative for screening. (See "Down syndrome: Overview of prenatal screening", section on 'Second trimester quadruple test'.)

If additional anomalies are noted, diagnostic testing for chromosomal abnormality (eg, Down syndrome) rather than a screening test is appropriate. Amniocentesis to obtain amniocytes for fetal karyotype or microarray will provide a definitive genetic diagnosis. (See "Down syndrome: Overview of prenatal screening", section on 'Diagnostic testing'.)

ULTRASOUND EXAMINATION

Renal and urologic examination — Detection of fetal hydronephrosis by ultrasound usually occurs in the second trimester with a renal pelvic diameter (RPD) cutoff of ≥4 mm when routine prenatal ultrasonography is performed. Mild hydronephrosis (RPD of 4 to 10 mm or Society of Fetal Urology [SFU] grade I or II) can be associated with Down syndrome or other chromosome anomalies. More severe dilation increases the risk of congenital anomalies of the kidney and urinary tract (CAKUT). (See 'Congenital anomalies of the kidney and urinary tract (CAKUT)' above.)

During the ultrasound examination, the appearance of the fetal renal system can vary in both normal fetuses without hydronephrosis and in those with hydronephrosis. Therefore, serial measurements should be taken during each examination [41].

If fetal hydronephrosis is detected, the following parameters need to be evaluated by ultrasonography, as they guide further need for evaluation and are helpful in determining the cause of hydronephrosis:

Moderate hydronephrosis – Surgical intervention performed in 11 of 43 cases (24 percent) for VUR (n = 3), UPJO (n = 5), PUV (n = 1), and unknown in 2 cases.

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Severe hydronephrosis – Surgical intervention performed in 13 of 19 cases (63 percent) for VUR (n = 2), UPJO (n = 8), and one case each of ureterovesical obstruction, prune-belly, and unknown.

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In a prospective French single center study of cases with severe prenatal hydronephrosis (defined as RPD >10 mm on first fetal examination), 33 of 70 (47 percent) patients had surgical intervention at a median age of five months [19]. Indications for surgery included recurrent febrile urinary tract infections and/or decrease of relative renal function more than 10 percent on serial renal scans. Dilation remained stable in 14 cases and decreased in 23 patients at a median follow-up of 42 months. A RPD >20 mm was the most accurate predictor for surgical intervention.

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A prospective study of 149 cases that performed serial ultrasounds prenatally at 20 and 30 weeks gestation and postnatally at 1, 6, and 12 months reported that thresholds of <6 mm at 20 weeks gestation and <10 mm at 30 weeks gestation accurately ruled out underlying obstructive uropathy that required surgical intervention [37].

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Results from a retrospective review of 280 infants who had two prenatal ultrasound examinations and a complete postnatal urological evaluation showed that the increasing or persistent dilation of fetal hydronephrosis (defined as an RPD between 5 and 10 mm on the first scan) was predictive of postnatal surgery [38]. The following is the total number of cases and those requiring surgery based upon RPD changes on the second compared with the first prenatal ultrasound.

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Complete resolution with normal RPD on second ultrasound − 5 cases (2 percent), of which 1 required surgery•

Reduced dilation but not complete resolution − 97 cases, of which 3 required surgery (3 percent)•

No change − 86 cases, of which 7 required surgery (8 percent)•

Increased dilation (RPD >10 mm on second scan) − 46 cases, of which 11 required surgery (24 percent)•

Severity and persistence of hydronephrosis (image 2 and image 3) – The likelihood of CAKUT increases with the severity of RPD (see 'Severity of hydronephrosis' above) [16,29,30]. Repeat ultrasound performed during the third trimester is more informative in predicting neonatal CAKUT, which may require surgical intervention. (See 'Definition and grading' above and 'Congenital anomalies of the kidney and urinary tract (CAKUT)' above.)

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Unilateral versus bilateral involvement – Bilateral involvement increases the risk of a significant renal abnormality and the risk of impaired postnatal renal function.

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Ureter − Dilation of the ureter can be consistent with vesicoureteral reflux (VUR) or obstructive uropathy distal to the ureteropelvic junction (eg, ureterocele (image 4 and figure 5), megaureter (figure 4), or posterior urethral valves [PUV] (image 7)). (See "Congenital ureteropelvic junction obstruction" and "Primary megaureter in infants and children" and "Ectopic ureter" and "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux".)

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Other anomalies — Other nonrenal/urinary tract congenital abnormalities are associated with fetal hydronephrosis [45-47]. Hydronephrosis has been reported as part of a multiple malformation syndrome in more than 60 genetic and sporadic malformation syndromes [45]. If other fetal structural abnormalities are identified, the fetus is at risk of having a chromosomal abnormality [46]. In this setting, a diagnostic test such as amniocentesis for fetal karyotype or microarray may provide a definitive genetic diagnosis. (See "Down syndrome: Overview of prenatal screening", section on 'Diagnostic testing'.)

MANAGEMENT

Overview — In our practice, further evaluation is performed for all fetuses noted to have renal dilation because of the potential risk for congenital anomalies of the kidney and urinary tract (CAKUT). We define fetal hydronephrosis as a renal pelvic diameter (RPD) >4 mm between 18 and 22 weeks gestation and >10 mm in the third trimester, or as Society of Fetal Urology (SFU) grade III or above. We believe this cutoff point of 10 mm provides a reasonable threshold to detect most fetuses at risk for CAKUT and to avoid unnecessary testing in cases with benign transient hydronephrosis [29] (algorithm 1).

Several factors are predictive of CAKUT including the increasing severity of fetal hydronephrosis, whether it is bilateral or unilateral, abnormally low amniotic fluid volume (eg, oligohydramnios), the presence of other anomalies (both renal and nonrenal abnormalities), maternal risk factors, and whether progression occurred. The presence of these findings directly impact management decisions, including need for further prenatal evaluation (eg, genetic testing and the timing and frequency of repeat ultrasounds) and postnatal evaluation (eg, imaging studies), and in some cases, surgical intervention.

We provide parents an explanation of all the ultrasound findings and their potential significance, the next steps of assessment, and if needed, prenatal and postnatal management options. In particular, if the fetal/neonatal prognosis is poor (ie, severe bilateral hydronephrosis, oligohydramnios, and evidence of thin or poorly developed renal parenchyma), legal termination, if possible, can be offered. (See "Postnatal management of fetal hydronephrosis".)

Further evaluation — The following is our evaluation approach for fetal hydronephrosis. Decisions are dependent on the presence and nature of associated renal and extrarenal anomalies, severity of hydronephrosis, unilateral versus bilateral involvement, gestational age (GA), and the amniotic fluid volume. In addition, decisions are made by a collaborative maternal-fetal team, consisting of a high-risk obstetrician, fetal ultrasonographer, and pediatric urologist.

Renal parenchyma − Thinning of the parenchyma and/or cortical cysts indicate injury or impaired development of the renal cortex. An echogenic renal cortex may indicate abnormal renal parenchymal development (dysplasia), which may be associated with VUR or obstruction.

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Bladder − Abnormalities of the bladder such as increased thickness and trabeculation of the bladder wall are consistent with obstructive uropathy distal to the bladder (eg, PUV). In addition, dilation of the proximal urethra (keyhole sign) may indicate PUV in male fetuses with a thickened bladder wall and hydronephrosis (image 7). Bladder enlargement can be defined as a sagittal diameter larger than the sum of gestational age (GA) in weeks (mm) + 2 mm [42,43].

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Ureteroceles may be visualized in the bladder and can cause bladder outlet obstruction if closely located to the urethra.

Amniotic fluid volume − Oligohydramnios is consistent with impaired renal function resulting in a decreased production of fetal urine (amniotic fluid). It is a consistent feature of severe renal disease, affecting either both kidneys or a solitary kidney. (See "Assessment of amniotic fluid volume" and "Oligohydramnios", section on 'Clinical manifestations and diagnosis'.)

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Presence of urinoma or urinary ascites:●

Urinoma is a fluid mass formed by extravasated urine encapsulated in the perirenal fascia. Urinomas are secondary to urinary obstruction such as PUV or ureteropelvic junction obstruction (UPJO). Although rare, the presence of a fetal urinoma is associated with a nonfunctional dysplastic ipsilateral kidney in 80 percent of cases [44].

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Urinary ascites can be secondary to spontaneous or iatrogenic rupture of the bladder and the renal calices due to lower obstruction and increased pressure, or rarely due to neurogenic bladder.

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Genetic counseling and testing – Genetic counseling and testing are offered if additional fetal anomalies are detected, in women of advanced maternal age, and in women with abnormal maternal serum screening tests during the first or second trimester. (See "Sonographic findings associated with fetal aneuploidy", section on 'Trisomy 21 (Down syndrome)' and "Genetic testing".)

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Management based on initial ultrasound findings (algorithm 1):●

For fetuses with unilateral hydronephrosis >4 mm in the second trimester, a follow-up ultrasound scan in the third trimester (32 to 34 weeks of gestation) is performed. Those with resolution (RPD <10 mm in the third trimester) have a low risk of clinically significant pathology, and do not need further antenatal or postnatal evaluation. Those with persistent hydronephrosis >10 mm require postnatal evaluation. Of note, some experts in the field do not repeat a third trimester ultrasound for fetuses with a RPD between 4 and 7 mm in the second trimester, but repeat a postnatal ultrasound at three to four weeks. (See 'Congenital anomalies of the kidney and urinary tract (CAKUT)' above and "Postnatal management of fetal hydronephrosis", section on 'Approach'.)

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Fetuses with bilateral hydronephrosis >4 mm and normal amniotic fluid volume have serial ultrasound examinations every two to three weeks after diagnosis to evaluate for progression of dilation and amniotic fluid volume. Follow-up examinations are determined according to the serial ultrasound results.

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Oligohydramnios – Management of oligohydramnios is dependent on the GA of the fetus, and is discussed separately. (See "Oligohydramnios".)

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Amniotic fluid analysis – Although oligohydramnios is the most reliable predictor of abnormal fetal renal function, its absence does not assure normal fetal renal function. Because amniotic fluid is predominantly composed of fetal urine, measurement of biochemical markers (ie, sodium and beta-2-microglobulin) contained in fetal urine can be used to assess fetal renal function. These tests are not clinically accurate enough to fully predict postnatal renal function, as discussed separately. (See "Evaluation of congenital anomalies of the kidney and urinary tract (CAKUT)", section on 'Amniotic fluid'.)

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Fetal surgery — Although there have been several prospective and retrospective studies of antenatal surgery in fetuses with sonographic findings consistent with lower urinary tract obstruction, there is no good evidence that fetal intervention improves renal outcome or long-term patient survival [47-54]. These procedures increase the amount of amniotic fluid, thus potentially improving lung development and survival rate. However, there remains a high rate of fetal demise and chronic renal disease in the survivors, necessitating renal replacement therapy (RRT) in almost two-thirds of cases [55]. In rare cases of post-bladder obstruction (primarily due to posterior urethral valves [PUV]), we would suggest contacting a tertiary referral center with experience with in utero intervention. In very rare cases with severe bilateral hydronephrosis due to post-bladder obstruction from PUV, we will consider serial fetal bladder taps for amniotic fluid analysis, and if the prognosis appears favorable, perform a vesicoamniotic shunt.

A randomized trial that aimed to determine if percutaneous vesicoamniotic shunting improves survival and renal outcome compared with conservative management could not be completed due to inability to recruit a sufficient number of cases, only enrolling 31 of the 150 planned pregnancies over a four-year period [56].

Although the authors suggest that shunting is associated with higher neonatal survival, the results from this study need to be interpreted carefully, as four of the fetuses who underwent shunting did not survive and the trial was limited by significantly too few cases and protocol deviation in a substantial number of the enrolled cases. Nevertheless, survival outcome in this study is consistent with the findings of observational studies that suggest the chance of postnatal normal renal function is low irrespective of whether or not vesicoamniotic shunting is performed.

If antenatal intervention is performed, it should only be performed in select centers with expertise after careful counseling of parents on the risk and benefits of the procedure, and available information on the neonatal survival and renal outcome.

The postnatal management of fetal hydronephrosis is discussed separately. (See "Postnatal management of fetal hydronephrosis".)

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SUMMARY AND RECOMMENDATIONS

However, because there are no other predictive tools, in our center we will perform bladder taps in some rare cases of post-bladder obstruction as part of the evaluation to predict renal prognosis for further intervention, including amnioinfusion and vesicoamniotic shunts. (See "Oligohydramnios", section on 'Amnioinfusion'.)

In an intention to treat analysis of the 31 enrolled women with singleton pregnancies (16 allocated to vesicoamniotic shunting versus 15 to conservative management), there was a trend for improved survival with shunting at 28 days (relative risk [RR] 1.88, 95% CI 0.71-4.96), one year (RR 2.19, 95% CI 0.69-6.94), and two years of age (RR 2.19, 95% CI 0.69-6.94). Outcomes for the 16 pregnancies allocated to vesicoamniotic shunting were 12 live births, one intrauterine death, and three terminated pregnancies; for the 15 pregnancies managed conservatively, there were 12 live births, one intrauterine death, and two terminated pregnancies. A significant number of cases did not receive the allocated intervention; 3 of the 16 pregnancies allocated to shunting were managed conservatively, and conversely, two cases randomized to conservative management had shunting.

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Due to large crossover, an analysis based on treatment was performed, which showed a larger beneficial effect of shunting on survival at 28 days (RR 3.2, 95% CI 1.06-9.62), one year (RR 4.27, 95% CI 1.07-16.96), and two years of age (RR 4.27, 95% CI 1.07-16.96). Only two offspring who survived to two years of age had normal renal function; both were in the shunt group. Seven complications occurred in six fetuses who were in the shunt group, and included spontaneous ruptured membrane, shunt blockage, and dislodgement, which resulted in four pregnancy losses. Postnatal diagnoses were made in all 12 perinatal survivors and in three neonates who died, and included nine cases of PUV (five in the shunt group and four in the conservative management group), five cases of urethral atresia (four in the shunt group and one in the conservative management group), and one case of urethral syrinx that caused obstruction (in the conservative management group). Diagnostic information was also available in three cases lost during pregnancy; two with urethral atresia, and one with PUV.

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Basics topics (see "Patient education: Prenatal hydronephrosis (The Basics)")●

Fetal hydronephrosis (fetal renal pelvic dilation) is a common finding on antenatal ultrasonography occurring in 0.6 to 4.5 percent of pregnancies. It can be detected as early as the 12 week of gestation. (See 'Epidemiology' above.)

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Although fetal hydronephrosis is most often transient or clinically insignificant, urinary tract obstruction or vesicoureteral reflux (VUR) are important causes that should be diagnosed soon after birth, because they are risk factors for pyelonephritis and renal impairment. (See 'Etiology' above.)

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Although there is lack of consensus with many different scoring systems for fetal hydronephrosis, renal pelvic diameter (RPD) is the most commonly used scoring system. Mild hydronephrosis is defined as an RPD of ≥4 to 10 mm and more severe hydronephrosis as an RPD >10 mm measured during the second trimester. Fetuses with RPD >15 mm during the third trimester are at the greatest risk for significant renal disease. In our practice we use a cutoff of >10 mm in the third trimester to determine the need for postnatal evaluation and intervention (algorithm 1). (See 'Ultrasound examination' above and 'Definition and grading' above.)

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In fetuses with increased RPD, ultrasonographic imaging should assess for the presence of caliectasis, parenchymal echogenicity, parenchymal thinning, presence of ureteromegaly, enlarged bladder size, and wall thickness, which if present, increase the risk of congenital anomalies of the kidney and urinary tract (CAKUT). (See 'Ultrasound examination' above.)

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Because fetuses with hydronephrosis are at increased risk for Down syndrome and CAKUT, a comprehensive prenatal evaluation is required for these conditions. (See 'Congenital anomalies of the kidney and urinary tract (CAKUT)' above and 'Down syndrome' above.)

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ACKNOWLEDGMENT — The editorial staff at UpToDate would like to acknowledge Tulin Ozcan, MD, who contributed to an earlier version of this topic review.

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13. Blachar A, Blachar Y, Livne PM, et al. Clinical outcome and follow-up of prenatal hydronephrosis. Pediatr Nephrol 1994; 8:30.

14. Pates JA, Dashe JS. Prenatal diagnosis and management of hydronephrosis. Early Hum Dev 2006; 82:3.

15. Ismaili K, Hall M, Donner C, et al. Results of systematic screening for minor degrees of fetal renal pelvis dilatation in an unselected

population. Am J Obstet Gynecol 2003; 188:242.

16. Lee RS, Cendron M, Kinnamon DD, Nguyen HT. Antenatal hydronephrosis as a predictor of postnatal outcome: a meta-analysis. Pediatrics

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The risk of renal and urinary tract abnormality increases with the severity of hydronephrosis, persistence of hydronephrosis into the third trimester, bilateral involvement, and the presence of oligohydramnios. (See 'Renal and urologic examination' above.)

●

Repeat antenatal ultrasound examinations are performed to help guide management decisions. The timing is dependent on findings on the initial examination. Fetuses with second trimester hydronephrosis (RPD >4 mm) should undergo repeat testing in the third trimester to assess progression and select those who will benefit most from postnatal testing (algorithm 1). In general, we perform a repeat examination two to three weeks later in fetuses with bilateral involvement (or an affected solitary kidney) and at 32 to 34 weeks gestation in those with unilateral involvement. (See 'Management' above.)

●

Data are limited on whether percutaneous vesicoamniotic shunting compared with conservative observation in fetuses with lower urinary tract obstruction improves survival and renal outcome. As a result, we do not suggest that percutaneous vesicoamniotic shunting be routinely performed in fetuses with lower urinary tract obstruction. If antenatal intervention is performed, it should only be performed in select centers with expertise after careful counseling of parents on the risk and benefits of the procedure, and available information on the neonatal survival and renal outcome. (See 'Fetal surgery' above.)

●

26. Havutcu AE, Nikolopoulos G, Adinkra P, Lamont RF. The association between fetal pyelectasis on second trimester ultrasound scan and

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natural history and referral pattern. Prenat Diagn 2012; 32:1242.

32. Anderson N, Clautice-Engle T, Allan R, et al. Detection of obstructive uropathy in the fetus: predictive value of sonographic measurements of

renal pelvic diameter at various gestational ages. AJR Am J Roentgenol 1995; 164:719.

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Obstet Gynecol Scand 1994; 73:290.

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2000; 16:60.

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postnatal pelviectasis. Tech Urol 1998; 4:198.

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postnatal referral. Ultrasound Obstet Gynecol 2005; 25:378.

37. Bassanese G, Travan L, D'Ottavio G, et al. Prenatal anteroposterior pelvic diameter cutoffs for postnatal referral for isolated pyelectasis and

hydronephrosis: more is not always better. J Urol 2013; 190:1858.

38. Signorelli M, Cerri V, Taddei F, et al. Prenatal diagnosis and management of mild fetal pyelectasis: implications for neonatal outcome and

follow-up. Eur J Obstet Gynecol Reprod Biol 2005; 118:154.

39. Coco C, Jeanty P. Isolated fetal pyelectasis and chromosomal abnormalities. Am J Obstet Gynecol 2005; 193:732.

40. Corteville JE, Dicke JM, Crane JP. Fetal pyelectasis and Down syndrome: is genetic amniocentesis warranted? Obstet Gynecol 1992;

79:770.

41. Persutte WH, Hussey M, Chyu J, Hobbins JC. Striking findings concerning the variability in the measurement of the fetal renal collecting

system. Ultrasound Obstet Gynecol 2000; 15:186.

42. The fetal genitourinary tract. In: Ultrasonography in Obstetrics and Gynecology, 5th ed, Callen PW (Ed), Saunders, Philadelphia 2007. p.647.

43. Maizels M, Alpert SA, Houston JT, et al. Fetal bladder sagittal length: a simple monitor to assess normal and enlarged fetal bladder size, and

forecast clinical outcome. J Urol 2004; 172:1995.

44. Gorincour G, Rypens F, Toiviainen-Salo S, et al. Fetal urinoma: two new cases and a review of the literature. Ultrasound Obstet Gynecol

2006; 28:848.

45. Limwongse C, Cassidy SB. Syndromes and malformations of the urinary tract. In: Pediatric Neprhology, 5th, Avner ED, Harmon WE, Niaudet

P (Eds), Lippincott Williams and Wilkins, Philadelphia 2004. p.93.

46. Damen-Elias HA, De Jong TP, Stigter RH, et al. Congenital renal tract anomalies: outcome and follow-up of 402 cases detected antenatally

between 1986 and 2001. Ultrasound Obstet Gynecol 2005; 25:134.

47. Harrison MR, Golbus MS, Filly RA, et al. Fetal hydronephrosis: selection and surgical repair. J Pediatr Surg 1987; 22:556.

48. Nassr AA, Shazly SA, Abdelmagied AM, et al. Effectiveness of vesico-amniotic shunt in fetuses with congenital lower urinary tract

obstruction: An updated systematic review and meta-analysis. Ultrasound Obstet Gynecol 2016.

49. Coplen DE. Prenatal intervention for hydronephrosis. J Urol 1997; 157:2270.

50. Crombleholme TM, Harrison MR, Golbus MS, et al. Fetal intervention in obstructive uropathy: prognostic indicators and efficacy of

intervention. Am J Obstet Gynecol 1990; 162:1239.

51. Holmes N, Harrison MR, Baskin LS. Fetal surgery for posterior urethral valves: long-term postnatal outcomes. Pediatrics 2001; 108:E7.

52. Morris RK, Malin GL, Khan KS, Kilby MD. Systematic review of the effectiveness of antenatal intervention for the treatment of congenital

lower urinary tract obstruction. BJOG 2010; 117:382.

53. Morris RK, Ruano R, Kilby MD. Effectiveness of fetal cystoscopy as a diagnostic and therapeutic intervention for lower urinary tract

obstruction: a systematic review. Ultrasound Obstet Gynecol 2011; 37:629.

54. Ruano R, Sananes N, Sangi-Haghpeykar H, et al. Fetal intervention for severe lower urinary tract obstruction: a multicenter case-control

study comparing fetal cystoscopy with vesicoamniotic shunting. Ultrasound Obstet Gynecol 2015; 45:452.

55. Aulbert W, Kemper MJ. Severe antenatally diagnosed renal disorders: background, prognosis and practical approach. Pediatr Nephrol 2016;

31:563.

56. Morris RK, Malin GL, Quinlan-Jones E, et al. Percutaneous vesicoamniotic shunting versus conservative management for fetal lower urinary

tract obstruction (PLUTO): a randomised trial. Lancet 2013; 382:1496.

Topic 6099 Version 30.0

GRAPHICS

Society of Fetal Urology grading system for hydronephrosis

Grade 0: no dilation (not shown). Grade 1: renal pelvis is only visualized. Grade 2: renal pelvis as well as a few, but not all, calyces are visualized. Grade 3: virtually all calyces are visualized. Grade 4: similar to Grade 3, but when compared with the normal centralateral kidney, there is parenchymal thinning.

Graphic 50549 Version 3.0

Bilateral pyelectasis measuring 4 mm on each side

Courtesy of Tulin Ozcan, MD.


Severe bilateral fetal hydronephrosis

Axial view of the fetal abdomen demonstrating spine and two kidneys with hydronephrosis in a second trimester fetus.

Courtesy of Thomas Shipp, MD.


Urinary tract dilation classification system for pediatric hydronephrosis

The Urinary Tract Dilation (UTD) Classification System describes the appearance of the urinary tract based on antenatal and postnatal presentation. The antenatal presentation (left column) is divided into normal, A1, and A2-3, and measurements between 16 and 27 weeks and ≥28 weeks gestation. A normal urinary tract is one with no urinary tract abnormalities and anterior posterior renal pelvic diameter (APRPD) measuring less than 4 mm between 16 and 27 weeks gestation and less than 7 mm ≥28 weeks gestation. A1 describes a normal urinary tract with 4 to <7 mm pelvic dilation at 16 to 27 weeks gestation or 7 to <10 mm ≥28 weeks gestation with or without central calyceal dilation. UTD A2-3 is for fetuses if there is APRPD ≥7 mm between 16 and 27 weeks gestation or ≥10 mm ≥28 weeks gestation, peripheral calyceal dilation, ureteral dilation, renal parenchymal, or bladder abnormalities. The postnatal presentation (right column) is divided into normal, P1, P2, and P3. Measurements are more reliable if taken 48 hours after birth or later. A normal urinary tract is one with no urinary tract abnormalities and APRPD <10 mm. P1 describes a normal urinary tract with APRPD 10 to <15 mm and/or central calyceal dilation. P2 describes APRPD ≥15 mm or peripheral calyceal dilation. P3 describes additional ureteral dilation, abnormal renal echogenicity or cysts, or bladder abnormalities regardless of APRPD measurement.

Pediatric Radiology, Multidisciplinary consensus on the classification of antenatal and postnatal urinary tract dilation (UTD classification system), Vol. 45, 2015, p. 787, Chow JS, Darge K, © Springer-Verlag Berlin Heidelberg 2015. With permission of Springer.


Ureteropelvic junction obstruction (UPJ)

Schematic diagram of ureteropelvic obstruction that demonstrates the location of a functional or anatomical abnormality resulting in renal pelvic dilatation.

Reproduced with permission from: Baskin LS, Kogan BA. Handbook of Pediatric Urology, 2nd ed, Lippincott Williams & Wilkins, Philadelphia 2005. Copyright © 2005 Lippincott Williams & Wilkins. www.lww.com.


International classification of vesicoureteral reflux (VUR)

Modified from: International Reflux Committee. Medical versus surgical treatment of primary vesicoureteral reflux. Pediatrics 1981; 67:392.


Primary megaureter

Schematic diagram of primary megaureter that demonstrates the location of a functional or anatomical abnormality at the ureterovesical junction.

Reproduced with permission from: Baskin LS, Kogan BA. Handbook of Pediatric Urology, 2nd ed, Lippincott Williams & Wilkins, Philadelphia 2005. Copyright © 2005 Lippincott Williams & Wilkins. www.lww.com.


Ureterocele



Ureteroceles in a right duplex collecting system

A ureterocele is a cystic dilation of a segment of the ureter contained within the bladder wall (ie, intravesical ureter). Intravesical ureteroceles are contained entirely within the bladder. Ectopic ureteroceles are partially situated at the bladder neck or urethra.


Voiding cystourethrogram of patient with posterior urethral valves

Arrows outline dilated urethra. Arrowheads outline dilated ureter with associated vesicoureteral reflux.

Courtesy of Nicholas Holmes, MD.


Left duplex collecting system



Thickened bladder wall and key hole sign with severe hydronephrosis in a 30 4/7 week old fetus with posterior urethral valves.

BL: bladder; RT: right kidney; LT: left kidney.



Contributor Disclosures

Laurence S Baskin, MD, FAAP Nothing to disclose Tej K Mattoo, MD, DCH, FRCP Nothing to disclose Louise Wilkins-Haug, MD,

PhD Nothing to disclose Duncan Wilcox, MD Nothing to disclose Melanie S Kim, MD Nothing to disclose

Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-

level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required

of all authors and must conform to UpToDate standards of evidence.

Conflict of interest policy

Overview evaluation of fetal hydronephrosis

Algorithm demonstrating an overview of the evaluation and management of fetal hydronephrosis detected in the second trimester of pregnancy.

RPD: renal pelvic diameter.* Refer to algorithm "Postnatal evaluation of unilateral hydronephrosis."¶ Refer to algorithm "Postnatal evaluation of bilateral hydronephrosis."


overview of fetal hydronephrosis -...

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