Antenatal Hydronephrosis David M. Kitchens, MD, and C.D. Anthony Herndon, MD

Corresponding author C.D. Anthony Herndon, MD University of Alabama at Birmingham, 1600 7th Avenue South, ACC #318, Birmingham, AL 35233, USA. E-mail: [email protected] Current Urology Reports 2009, 10:126–133 Current Medicine Group LLC ISSN 1527-2737 Copyright © 2009 by Current Medicine Group LLC

The diagnosis, workup, and management of prenatal hydronephrosis have undergone a swing from preemptive surgical treatment to a more conservative approach as the natural history of the differential diagnoses becomes more appreciated. We examine different radiologic tests for determining the diagnoses associated with antenatal hydronephrosis. A review of the more common differential diagnoses of prenatal hydronephrosis and current treatment options for ureteropelvic junction obstruction, vesicoureteral reflux, ureteroceles, ectopic ureters, and megaureters is undertaken.

Introduction Routine fetal sonography, typically carried out in the mid second trimester, has significantly changed the presentation, evaluation, and management of prenatal hydronephrosis. Fetal intervention is rarely indicated and only plays a small role in the management of any patient presenting with prenatal hydronephrosis. Ureteropelvic junction obstruction (UPJO) is by far the most common entity detected. The neonate with prenatal hydronephrosis should undergo a thorough evaluation of the upper and lower urinary tracts. A recent meta-analysis has reiterated the importance of the postnatal evaluation of antenatal hydronephrosis because 12% to 88% of these children will have demonstrable pathology depending on the degree (mild, moderate, severe) of prenatally detected hydronephrosis [1••]. If there is no evidence of bladder outlet obstruction, the infant may leave the hospital shortly after birth. Immediate intervention for most of the common diagnoses detected antenatally such as UPJO and primary obstructing megaureter has decreased over the past two decades. This review better clarifies these issues and demonstrates a contemporary algorithm to manage prenatal hydronephrosis.

Fetal Detection and Follow-Up Fetal ultrasound The accepted standard for anterior posterior (AP) pelvic dilation considered to be significant is based on the original work by Corteville et al. [2]. In their series, a renal pelvis AP diameter of greater than 4 mm at 33 weeks’ gestational age (GA) or greater than 7 mm at 40 weeks’ GA demonstrated a sensitivity of 100% for the identification of those patients with abnormal renal function or those who required subsequent intervention postnatally. With these data, Corteville et al. [2] identified an upper limit threshold of antenatal hydronephrosis that warrants postnatal evaluation. Other centers have offered an alternate view by identifying a lower limit threshold for patients with nonsignificant prenatal renal pelvis dilation. Siemens et al. [3] demonstrated prenatal renal pelvis AP thresholds of less than 6 mm (< 20 weeks’ GA), less than 8 mm (20–30 weeks’ GA), and less than 10 mm (> 30 weeks’ GA) to be predictive of those patients who did not manifest postnatal urologic disease. In addition to characterizing hydronephrosis, the antenatal ultrasound should document the level of amniotic fluid, cycling of the urinary bladder, an attempt at visualization of a ureter, the presence of a contralateral kidney, characterization of renal cysts, and the presence of other organ system abnormalities. When a severe abnormality is detected, the general recommendation is to follow this with 2- to 4-week interval ultrasound. If a deterioration of the clinical setting occurs (eg, worsening oligohydramnios), then antenatal intervention with fetal shunting may be indicated. Fluctuations in fetal renal and ureteral biometrics may occur during serial gestational imaging. Bobrowski et al. [4] reported that minimal pelvic dilation progressed to hydronephrosis defi ned as greater than 10 mm in 11% of fetuses. Bilateral dilation was more predictive of progression in their population, representing 80% of the entire cohort that progressed. Additionally, severe antenatal hydronephrosis (> 20 mm) may be underrepresented on initial postnatal imaging and subsequently return to prenatal levels, necessitating delayed surgical intervention [5]. Some have reported that renal pelvis fluctuations associated with fetal voiding, the presence of ureteral dilation, and progression to hydronephrosis may be predictors of vesicoureteral reflux (VUR) [6].

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Table 1. Society for Fetal Urology hydronephrosis grading system Grade 1

Renal pelvis splitting

Grade 2

Moderate renal pelvis splitting confined to renal border

Grade 3

Significant renal pelvis distention outside of renal border, uniform calyceal distention, renal parenchyma normal

Grade 4

Significant renal pelvis distention, significant calyceal distention, renal parenchyma demonstrates thinning

(Adapted from Fernbach et al. [8].)

When using the accepted standards set forth by the Corteville group, antenatal hydronephrosis has been seen in up to 4.5% of all pregnancies. The report from the Brussels Free University Perinatal Nephrology study group revealed that 62% of infants with antenatal hydronephrosis demonstrated a renal anomaly, but only 39% were significant uropathies. Of this group, a minority required actual surgical intervention. Furthermore, with the identification limited to only the second trimester, the detection rate of significant renal disease fell to 12% [7]. The Society for Fetal Urology (SFU) developed a standardized evaluation system designed in part to help predict patients who may need surgical intervention postnatally [8]. This classification system incorporates collecting system dilation in addition to parenchymal integrity. The system is a spectrum, with grade 1 demonstrating normal parenchymal thickness and only renal pelvis splitting, and grade 4 revealing distention of the renal pelvis and calyces in addition to parenchymal thinning (Table 1). Limitations exist with the SFU classification scheme; variables such as renal length in relation to GA may improve the predictive value of this system.

Maternal/fetal MRI Maternal/fetal MRI is still in its infancy. Widespread application is limited by cost and access. To date, only a handful of case reports are available in the literature [9]. However, MRI remains an attractive imaging modality because of the absence of fetal radiation exposure and superior resolution when compared with maternal ultrasound.

and low amniotic fluid will exist in the patient with urethral valves, but this is not absolute. The clinician should have a high index of suspicion when evaluating any male with a history of bilateral hydronephrosis. The pediatric urologist should be involved as soon as possible, ideally in the antenatal period. After delivery, a 5 French feeding tube should be placed in the urinary bladder. A renal ultrasound should be performed on the fi rst day of life and the child placed on prophylactic antibiotics. The VCU should be performed to confi rm the diagnosis, and the child should be transferred to a tertiary center with the feeding tube decompressing the urinary bladder.

Normal initial postnatal ultrasound In the presence of a normal postnatal ultrasound, a repeat study is recommended at 4 weeks of age. If the second study is also normal, in the absence of VUR, then no further imaging is necessary. The Brussels Free University Perinatal Nephrology Study Group reported a prospective review of patients with mild to moderate antenatal hydronephrosis. In this review, 213 infants (139 boys, 74 girls) with antenatal mild to moderate hydronephrosis were followed at day 5, and months 1, 3, 6, 12, and 24. Eighty-one infants (38%) demonstrated a normal evaluation at birth. In all cases, the examination remained normal throughout the 24-month follow-up period [10]. However, delayed presentations of UPJOs with normal postnatal ultrasounds have been reported, and parents should be advised of this [11].

Abnormal initial postnatal ultrasound

Postnatal Evaluation The postnatal evaluation of antenatal hydronephrosis should include a thorough evaluation of the upper and lower urinary tract. Until the etiology of antenatal hydronephrosis is determined, amoxicillin prophylaxis is recommended. A number of imaging modalities, including renal ultrasound, voiding cystourethrogram (VCU), and radionuclide renal scan imaging, may be required.

Evaluation of bilateral hydronephrosis in a male Any male fetus with antenatal bilateral hydronephrosis and a dilated bladder should be presumed to have posterior urethral valves. Typically, SFU grade 3 or 4 hydronephrosis, hydroureter, renal dysplasia, a thickened bladder wall,

If the initial ultrasound is abnormal, then a repeat ultrasound is recommended at 1 month. A contemporary standard does not exist for follow-up of SFU grades 1 and 2 hydronephrosis. Also, a controversy exists in the literature concerning the need for long-term follow-up of mild hydronephrosis. Interpretation of the literature is limited by the lack of agreement in terminology of hydronephrosis before implementation of the SFU grading system. In 2001, Sairam et al. [12] evaluated the natural history of midtrimester hydronephrosis. In their review of 268 women, mild (4–10 mm) hydronephrosis was seen in 80% of the fetuses. Of this group, none required surgical intervention postnatally. Furthermore, 88% of this cohort resolved the hydronephrosis in the antenatal or neonatal period. In contrast,

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Figure 1. Postnatal evaluation of antenatal hydronephrosis. AP—anterior posterior; BOO—bladder outlet obstruction; DMSA—dimercaptosuccinic acid renal scan; Nml—normal; PBS—prune belly syndrome; PUV—posterior urethral valves; qd—every day; RBS—renal/bladder ultrasound; SFU—Society for Fetal Urology; US—ultrasound; VCU—voiding cystourethrogram. (From Herndon [42]; with permission.)

some reports raise question to the benign nature of mild pelvic dilation. Looking at the Brussels study of 213 infants with mild to moderate antenatal hydronephrosis, significant uropathies were seen in 39% of the infants, although intervention was not required in most patients [7]. A recent report by Signorelli et al. [13] demonstrated that up to 24% of patients with worsening of mild fetal pelvis dilation may require subsequent intervention. In contrast, Odibo et al. [14] reported an AP renal pelvis diameter threshold of 7 mm as predictive of normalization of postnatal studies. Currently, most children with SFU grade 1 and 2 hydronephrosis are followed until they are mature enough to verbalize signs of distress. The ideal follow-up protocol for mild forms of hydronephrosis can only be resolved with a multicenter prospective trial. For SFU grade 3 or 4 hydronephrosis, a radionuclide renal scan may be needed. In the setting of bilateral hydronephrosis, the threshold for obtaining a radionuclide scan is much lower. Subsequent imaging studies for upper tract dilation should be based on the results of the VCU and the radionuclide renal scan (Fig. 1).

Voiding cystourethrogram A lack of agreement exists concerning the need for a postnatal VCU in the presence of antenatal hydronephrosis. The overall incidence of reflux in a population with antenatal hydronephrosis ranges from 8% to 38% [15,16]. Factors such as the presence of ureteral dilation prenatally, the degree of pelvic dilation, race, and the presence of hydronephrosis have been reported to impact the results of the VCU. A number of centers, including one multicenter review, have reported the initial postnatal ultrasound to be normal in up to 25% of patients with VUR who were identified with antenatal hydronephrosis [6,16]. The timing of the postnatal VCU should be individualized with each patient. In cases of suspected bladder outlet obstruction, it is imperative to exclude this diagnosis within the fi rst days of life. In cases of possible VUR, a VCU is recommended within 1 month of life. Although it would be ideal to exclude VUR as soon as possible in order to take these children off of prophylaxis, it is not practical for some families to do so because of transportation issues.

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Radionuclide renal scan When concerns for obstruction exist, a “well-tempered diuretic diethylene triamine pentaacetic acid (DTPA) or mercaptoacetyltriglycine (MAG-3) renogram” should be performed [17]. This is a dynamic modality that provides relative function and drainage to aid the urologist in assessing the obstructive nature of antenatal hydronephrosis. Of the two available agents, MAG-3 is preferred because of its favorable renal secretion properties. As with all studies, limitations exist and the effi cacy of this modality varies signifi cantly in the literature. Several important steps deserve mention. First, all patients should have a catheter placed in order to eliminate bladder pressure and prevent reflux of radionuclide. Second, furosemide should be administered with an appropriate dose at the point of maximal tracer uptake. Third, intravenous hydration is required in all patients. Despite these guidelines, signifi cant variances have been reported. Some centers have demonstrated a signifi cant alteration in relative function based on the size of the region of interest (ROI). The Great Ormond Street group reported that the relative variability of the ROI in the larger hydronephrotic kidney may explain the common fi nding of supranormal renal function [18]. In another study, Takla et al. [19] reported on 51 patients with antenatal hydronephrosis. Normalization of renal function and washout was demonstrated in 55%. The initial drainage curve was predictive of those patients who eventually normalized their studies. Normalization of renal drainage and function occurred in 86% of patients with an initial nonobstructive curve, 62% with an indeterminate scan, and 18% with an initial obstructive curve. In contrast, Hafez et al. [20] reported that the initial drainage curves from the initial renogram were not predictive of those patients requiring surgical intervention for UPJO.

MRI urography As an imaging modality, MRI urography (MRU) offers the advantages of providing superior imaging detail and functional assessment of obstruction without neonatal radiation exposure. The Emory group presented a recent report comparing MRU to conventional studies such as renal ultrasound and radionuclide renal scans. They concluded that MRU offered comparable results in terms of renal function and superior anatomic detail [21]. However, issues such as cost, availability, and the need for sedation in most patients significantly limit the widespread application of this imaging modality.

Antibiotic Prophylaxis Antibiotic prophylaxis should be administered until all studies have been completed. Two milliliters of amoxicillin daily (125 mg/5 mL) is preferred. Devastating infections

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have been reported when patients known to have antenatal hydronephrosis are not appropriately managed postnatally [22]. Some studies have indicated that circumcision status may impact the infection rate in the presence of a known renal anomaly [6,23]. After 3 months, the amoxicillin may be switched over to nitrofurantoin (1/2 of a 25-mg capsule) or trimethoprim/sulfamethoxazole (1/2 tsp/10 kg).

Ureteropelvic Junction Obstruction Although prenatal detection of suspected UPJO initially triggered a preemptive surgical approach, the current treatment regimen is more conservative [24]. This conservative approach of “watchful waiting” was initially reported by Koff [24]. In this study of 104 newborns with unilateral severe hydronephrosis who were managed expectantly, only 23 required intervention for documented deterioration of renal function. In addition, hydronephrosis resolved in 69% and improved in 31%. The average time to this resolution was 2.5 years [25]. The most comprehensive study reported in regard to a surgical versus an observational approach to UPJO was presented by Dhillon [5] from the Great Ormond Street Hospital. The inclusion criteria were an AP renal pelvic diameter more than 15 mm postnatally, calyceal dilation, and differential function of 40% or more. Seventy-five patients (53 boys) were enrolled. Both groups were comparable in terms of mean hydronephrosis and differential function. Thirty-nine patients underwent surgical intervention, with only one patient demonstrating a decrease in renal function postoperatively. Of the 36 patients in the observation group, only seven patients required surgical intervention for renal deterioration. Renal function was able to be recovered in all but one patient postoperatively. AP diameter appeared to predict those patients requiring intervention. All seven of the patients who crossed over to the intervention group demonstrated an AP diameter of more than 20 mm (20–40 mm). However, nine of 17 of the patients with spontaneous resolution also initially demonstrated an AP diameter of more than 20 mm. Data obtained from renal scans can also be misleading as far as determining which renal units require surgical intervention. Elder et al. [26] compared renal biopsy data with preoperative renal scan differential function data. Interestingly, in the group with less than 40% differential function, 25% demonstrated essentially normal fi ndings on renal biopsy. In the group with normal renal function, 21% demonstrated abnormal renal histology. The accuracy of the “well-tempered” renal scan in diagnosing significant obstruction is controversial at best, and MRU may hold future promise in helping to determine which hydronephrotic kidneys require intervention [27]. All patients considered for intervention can be placed on antibiotic prophylaxis until it is determined whether

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surgical repair is necessary, although this is controversial. All patients should undergo a renal ultrasound on day 2 of life and VCU soon thereafter. The use of MRU for diagnosis of UPJO has been hindered at our institution by the fact that sedation is required in patients younger than 7 years of age for accurate imaging. Also, patients under 6 months of age at our institution cannot receive sedation, and it is usually of utmost importance to determine whether intervention is required before this age if renal function is to be salvaged. Therefore, we still utilize a diuretic renal scan in select cases of grade 3 and 4 hydronephrosis, in which UPJO only is suspected. A repeat ultrasound and “well-tempered” renogram should be performed at 4 to 6 weeks of life. In the select case of a severely obstructed drainage curve or demonstrative decrease in differential function (< 40%), immediate intervention should be employed. In most patients, intervention can be deferred and a repeat ultrasound obtained at 3 months of age. If the renal ultrasound worsens or shows increased signs of distention, then a repeat “well-tempered” renal scan should be performed. In the authors’ opinion, surgical intervention, either an open or minimally invasive approach, is reserved for an obstructive drainage curve or indeterminate curve with a deterioration in renal function (< 40%). Close follow-up is mandatory for grade 3 and 4 hydronephrosis that is managed nonoperatively.

Vesicoureteral Reflux VUR will present in a bimodal distribution. VUR is most commonly diagnosed after an evaluation for a urinary tract infection. This typically will occur in females from 3 to 5 years of age. Separate from this population will be a different group that presents prenatally with hydronephrosis. These patients, aside from the hydronephrosis, will typically be asymptomatic. Ideally, they should be already on some sort of prophylaxis prior to their VCU. Antenatal reflux occurs predominately in boys and is high-grade and bilateral in most. Although most of these patients will be evaluated without having developed a urinary tract infection, a significant number will present with renal cortical defects presumed to be renal dysplasia [28]. Historical reflux resolution curves developed in conjunction with the American Urological Association do not apply to the child with antenatally detected VUR. Antenatal reflux appears to have a steeper resolution curve in comparison to reflux that is detected postnatally. An explanation may in part be due to delayed maturation of the sphincter/bladder neck mechanism evidenced by elevated voiding pressures [6,29,30]. In 1999, Herndon et al. [6] presented a multicenter report of VUR detected with antenatal hydronephrosis. A total of 71 patients (56 boys) representing 116 refluxing units were reviewed. High-grade VUR demonstrated a reflux resolution rate

of 20% at a mean of 0.9 years in boys and 2.1 years in girls. Circumcision status significantly impacted the infection rate and need for surgical intervention despite antibiotic prophylaxis. They recommended an initial interval of medical observation in all patients regardless of the grade of VUR. Controversy does exist surrounding the need for a postnatal VCU in all patients with antenatal hydronephrosis regardless of SFU grade [31]. The opponents of a postnatal VCU argue that no study to date has proven its efficacy and radiation exposure to the infant is greater than the odds of detecting VUR. The authors’ argument in favor of a postnatal VCU is fairly simple. If you feel that VUR is a disease, then one should test for its presence when presenting prenatally with hydronephrosis. When VUR is diagnosed, the practitioner should take a conservative approach. Amoxicillin prophylaxis (2 mL of 125 mg/5 mL) should be administered until 3 months of age. The child may be transitioned over to nitrofurantoin or trimethoprim/sulfamethoxazole prophylaxis at 3 months of age. A renal ultrasound should be performed every 6 months and VCU performed yearly. Indications for surgical intervention should not change even in the era of subureteric injection. Absolutely no evidence-based medicine exists supporting an approach that favors surgical intervention over prophylaxis or no medication in a child who has never developed a urinary tract infection. However, if indications for surgical intervention are met (ie, breakthrough urinary tract infections), then corrective surgery should be performed. The surgical options include open ureteral reimplantation or cystoscopic subureteric injection.

Duplication Anomalies (Ureterocele/Ectopic Ureter) Renal duplication anomalies may present antenatally with hydronephrosis. Typically, however, segmental hydronephrosis is identified in addition to a dilated ureter. The dilated ureter can be traced toward the urinary bladder where the identification of a ureterocele can be made by visualizing a cystic structure within the urinary bladder on ultrasound. The absence of this structure allows the presumptive diagnosis of an ectopic ureter to be made. Rarely will prenatal intervention be required in this situation. However, an obstructing prolapsing ureterocele may result in bladder outlet obstruction and resultant oligohydramnios. In this rare situation, fetal intervention may be required. Ureterocele puncture may suffice; however, vesicoamniotic shunt placement may be required if the puncture is not adequate to decompress the ureterocele. Postnatal imaging should include a renal and bladder ultrasound, VCU, and radionuclide scan, which can be done electively. These require catheterization, and to mini-

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mize trauma to the child from repeated catheterizations, the renal scan should be performed first. Reflux is common in duplication anomalies, especially in the laterally displaced lower pole moiety ureteral orifice. The renal scan aids in the assessment of function to the upper pole moiety, which corresponds to the dilated ureter. The patient diagnosed with an ectopic ureter or ureterocele will require surgical intervention. A determination should be made as to whether the affected renal unit is a single or duplex system. Eighty percent of ureteroceles will be duplex. The entire surgical plan should be based around the goal of maximizing renal function. For example, if the upper pole demonstrates minimal function and the ureter is markedly dilated, then an upper pole heminephrectomy would be in order. These decisions are based on the results of the radionuclide scan that can assess both the upper and lower pole moieties. Incision or puncture of the ureterocele should be utilized when the child presents with sepsis or bladder outlet obstruction, or in the presence of a single system. If the upper pole shows no function on the renal scan, then an upper pole heminephrectomy may be performed. The rationale behind this approach is to minimize the risk of infection in a dilated and obstructed system and to reduce the chances of involvement of the lower pole moiety in this process. Based on several papers from the Mayo Clinic, Husmann et al. [32–34] concluded the following: The need for subsequent intervention is based on whether or not the lower pole moiety refluxes and to what degree. In the setting of no VUR, intervention at the bladder level was not required. For low-grade reflux, bladder level intervention was performed in 40%. However, when the lower pole moiety demonstrates high-grade VUR, up to 96% of patients may require intervention at the level of the urinary bladder.

Husmann et al. [32–34] concluded that complete reconstruction, that is upper pole heminephrectomy with excision of ureterocele and reimplantation of the ureter as opposed to upper pole heminephrectomy alone, may be a reasonable approach. Recently, however, some authors have presented data supporting the role of incision of the ureterocele with reimplantation of the nonfunctioning upper pole. The short-term followup of these patients is encouraging; however, long-term (> 20 year) follow-up of the reimplanted nonfunctioning upper pole is lacking [35]. If the upper pole demonstrates function, then reimplantation of both ureters at the bladder level, upper to lower pole ureteroureterostomy at the kidney or bladder level, or incision of the ureterocele may be performed.

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Megaureter In order to classify the antenatally detected megaureter, a VCU and MAG-3 renal scan should be performed. Once the diagnosis of a nonrefluxing megaureter is made, then conservative medical observation should be fi rst-line therapy. Antibiotic prophylaxis is generally recommended for severe hydronephrosis and should follow the guidelines outlined above. Indications for surgical correction include deterioration in renal function (< 40%), infection, or pain. Based on the available literature, this should represent about 10% to 20% of the nonrefluxing megaureters. After the diagnosis is made, an initial conservative approach should be followed. Several recent reviews all with long-term follow-up have demonstrated a consensus toward a more conservative approach to patients with antenatally detected megaureters [36,37]. In the Boston series of 69 nonrefluxing megaureters, initial grade of hydronephrosis was a significant predictor of resolution. Grades 1 to 3 hydronephrosis resolved at a mean of 13, 24, and 35 months, respectively, compared with an average of 49 months for greater than grade 3 hydronephrosis. The Philadelphia series included the longest follow-up, with a mean of over 6 years in 27 patients representing 40 megaureters. Complete resolution of hydronephrosis occurred in 52% of patients at an average of 2.9 years. Long-term follow-up was available for 10 patients at a mean of 13.4 years. Of this group, one patient deteriorated asymptomatically with a reduction of renal function and the development of a contralateral renal stone. None of the four patients with resolved hydronephrosis redeveloped dilation [37]. Finally, a recent single-center series of 79 children detected prenatally determined that SFU grade 3 to 4 hydronephrosis, renal function of less than 30%, and ureteral diameter of 1.33 cm were predictive factors favoring surgical intervention in 25 (31%) of patients at a mean age of 14 months [38]. Various surgical approaches have been described for the megaureter, depending on the age at intervention. Typically, patients younger than 6 months of age should undergo diversion. Various levels and techniques have been described that are beyond the scope of this review. Generally, adequate decompression affords time for the child to grow until an adequate size and age are reached in order to proceed with reimplantation. In most situations, ureteral tapering or plication is needed at the time of reimplantation. However, Kitchens et al. [39] recently presented data refuting this dictum. In 23 renal units that underwent undiversion, only five (22%) required ureteral tailoring. If surgical indications do arise after 1 year of age, then undiversion may be avoided and reimplantation performed. In situations in which a 5:1 ureteral diameter to tunnel length cannot be met, then ureteral tailoring may be required. Ureteral plication offers the advantage of a nonexcisional option but creates more

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bulk and a larger tunnel to accept the ureter. Excisional tapering provides an effective means to decrease ureteral diameter without creating the excessive bulk associated with plication [40,41].

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Conclusions The management of antenatal hydronephrosis has trended toward a more conservative approach over the past few decades. An individualized but thorough workup should be undertaken for every neonate with antenatal hydronephrosis. Antibiotic prophylaxis should be initiated shortly after birth and continued at least until a diagnosis is reached. The SFU grading system for hydronephrosis should be utilized at all institutions. The initial renal ultrasound should be deferred until 48 hours of life. Although the role for VCU continues to be controversial, the literature appears to support its use for all patients with antenatal hydronephrosis. If bladder outlet obstruction is suspected, then the VCU should be performed within the fi rst days of life. Radionuclide renal scans may be useful as a guide for intervention by documenting differential function and drainage of the severely hydronephrotic kidney. Specific issues related to antenatal hydronephrosis yet to be resolved that warrant future study include appropriate follow-up of SFU grades 1 to 2 hydronephrosis in the absence of VUR, a consensus on which patients with SFU 3 and 4 hydronephrosis deserve surgical intervention, and a randomized trial for fetal intervention in the setting of bladder outlet obstruction.

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Disclosures No potential confl icts of interest relevant to this article were reported. 18.

References and Recommended Reading Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance 1.••

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