Congenital ureteropelvic junction obstruction

INTRODUCTION — Ureteropelvic junction (UPJ) obstruction is a partial or intermittent blockage of the flow of urine that occurs where the ureter enters the kidney. The etiology of UPJ obstruction includes both congenital and acquired conditions. UPJ obstruction is the most common pathologic cause of antenatally detected hydronephrosis.

The epidemiology, pathophysiology, clinical features, and management of congenital UPJ obstruction will be reviewed here.

EPIDEMIOLOGY — The reported incidence of UPJ obstruction is 1 in 500 live births screened by routine antenatal ultrasound; however, not all cases require surgical intervention [1,2]. UPJ obstruction is the most common anatomical cause of antenatal hydronephrosis.

Boys are affected with UPJ obstruction more commonly than are girls [3,4]. Lesions are found more frequently on the left than on the right side. The reported rate of bilateral involvement is approximately 10 percent [1,4].

PATHOPHYSIOLOGY — Congenital UPJ obstruction is caused by anatomic lesions or functional disturbances that restrict urinary flow across the UPJ, resulting in hydronephrosis (figure 1 and picture 1) [1]. Most cases are thought to be due to partial obstruction because complete obstruction results in rapid destruction of the kidney. In some cases, partial obstruction may also lead to progressive deterioration of kidney function. However, in many infants, an equilibrium state may develop in which kidney function remains stable.

Development of the equilibrium state resulting in stable kidney function depends on:

●Urinary rate and output

●Anatomy and degree of UPJ obstruction

●Compliance of the renal pelvis

In the fetus and infant, the renal pelvis, because of its increased compliance, can stretch and thereby accommodate large volumes of urine, which results in pelvic dilatation (hydronephrosis). The large capacity volume of a stretched pelvis decreases the risk of high intrapelvic pressure. As a result, kidneys with a large intrarenal pelvis are less vulnerable to damage from obstruction than those with a small intrarenal pelvis, especially during diuresis.

ETIOLOGY — Congenital UPJ obstruction is usually caused by intrinsic stenosis or less commonly crossing vessel causing external compression of the ureter at the UPJ. In older children, a rare cause of UPJ obstruction is a benign intraluminal ureteral polyp. If surgical correction is deemed appropriate, preoperative determination of the underlying cause is not necessary since the technique of reconstruction remains the same regardless of UPJ etiology and the exact etiology can be made intraoperatively.

●Intrinsic narrowing – In most cases of UPJ obstruction, the upper segment of the ureter is narrowed at the UPJ or kinked as the ureter enters the pelvis, resulting in obstruction of urinary flow (picture 2). Although the underlying mechanism is not proven, it is thought that there is an embryologic disruption of the proximal ureter that alters circular musculature development and/or collagen fibers, and composition between and around the muscular cells [5].

Rare causes of intrinsic UPJ obstruction include valvular mucosal folds, persistent fetal ureteral convolutions, and ureteral polyps (image 1 and movie 1).

●Crossing vessel – In approximately 10 percent of pediatric UPJ obstruction, an aberrant or accessory renal artery may cross the lower pole of the kidney, resulting in intermittent compression of the UPJ and blockage of urinary flow (picture 3 and image 2 and movie 2). It is possible to identify crossing vessels that cause extrinsic obstruction on computed tomography (CT) scan or magnetic resonance imaging (MRI), which are typically obtained for abdominal pain evaluation or other unrelated pathologies.

●Ureteral polyp – Less than 1 percent of pediatric UPJ obstruction (picture 3 and image 2 and movie 2) is caused by an intraluminal ureteral polyp(s) that typically presents with intermittent flank pain. Prospective diagnosis is often difficult, with the polyp typically found at the time of operative repair, although on occasion the polyp(s) may be suspected on preoperative sonogram, CT scan, or MRI.

CLINICAL PRESENTATION

Infants

●Prenatal hydronephrosis – In geographic areas where prenatal ultrasound screening is commonly performed, most cases of UPJ obstruction are diagnosed during the postnatal evaluation of antenatal hydronephrosis (image 3) [6] (see "Fetal hydronephrosis: Etiology and prenatal management")

●Postnatal presentation – In the absence of prenatal screening, infants may present with a palpable abdominal mass caused by an enlarged obstructed kidney. Other presentations include urinary tract infection, hematuria, or poor weight gain. Kidney failure is an unusual presentation and occurs in infants with a single obstructed kidney or with bilateral involvement.

Older children — Clinical manifestations in older children include intermittent flank pain or abdominal pain (referred to as Dietl's crisis). The pain may worsen during brisk diuresis (for example, after consumption of caffeine). These symptoms may be accompanied by nausea and vomiting, leading to an evaluation of the gastrointestinal tract [7]. Children may also present with hematuria, kidney stone, acute pyelonephritis [8], hypertension or kidney injury after experiencing minor trauma, [7-10]. UPJ obstruction may also present as an incidental finding on ultrasound for other conditions (image 3); or as a finding on computed tomography (CT) performed for abdominal pain of unknown etiology (image 4). (See "Emergency evaluation of the child with acute abdominal pain", section on 'Imaging'.)

Other anomalies — UPJ obstruction may be associated with other genitourinary anomalies, such as a horseshoe kidney [11], or be a component of or associated with a syndrome such as CHARGE (coloboma, heart anomaly, choanal atresia, retardation, genital and ear anomalies) syndrome [12].

DIAGNOSIS — The diagnosis of UPJ obstruction is generally suspected when ultrasonography demonstrates significant hydronephrosis with evidence of calyceal and renal pelvic dilatation without ureteral involvement (ie UPJ-type hydronephrosis) (image 3). Confirmation of UPJ obstruction is based on further imaging studies. In our center, the confirmatory diagnostic imaging differs between infants and older children.

Many infants with UPJ obstruction come to medical attention because significant hydronephrosis was detected on antenatal ultrasound. Details regarding the initial evaluation of newborns with antenatally diagnosed hydronephrosis, including the timing of postnatal ultrasound, are discussed separately. (See "Postnatal evaluation and management of hydronephrosis".)

Infants — UPJ obstruction is the most common cause of antenatal hydronephrosis. It should be suspected in infants with persistent hydronephrosis with renal pelvic diameter (RPD) >15 mm on postnatal ultrasound. The diagnosis of UPJ obstruction is typically confirmed with diuretic renal scan, although magnetic resonance imaging can also be used to make the diagnosis.

●In our center, diuretic renal scan (renal scan and the administration of a diuretic [typically furosemide]) is used to diagnose UPJ obstruction and other causes of obstructive uropathy. The preferred radioisotope is technetium-99m-mercaptoacetyltriglycine (Tc-99m MAG3), which is taken up by the renal cortex, filtered across the glomerular basement membrane (GBM) to the renal tubules, and excreted into the renal pelvis and urinary tract. The diuretic renal scan measures the drainage time from the renal pelvis (referred to as washout) and assesses the percent relative function of each kidney. The washout measurement correlates with the degree of obstruction. In general, we use a half-life greater than 20 minutes indicating delayed transient time of the TC-99m isotope from the kidney as an indication of significant UPJ obstruction. Another indicator of obstruction is a difference greater than 10 percent in split renal. Thus, patients with a half-life greater than 20 minutes or >10% difference in split function (for example, >60 percent on the right and <40 percent on the left) will need close monitoring and/or consideration of surgical correction. A more complete description of the diuretic renography is found separately. (See "Postnatal evaluation and management of hydronephrosis", section on 'Diuretic renography'.)

When a diuretic renal scan is being considered, referral to a center with expertise in pediatric urologic care is warranted because the renal scan is an invasive procedure, requiring placement of an intravenous line and bladder catheter in infants and children prior to toilet training. In general, diuretic renography can be performed after six weeks of life because immediate surgical intervention is rarely required, and the diuretic renography is more difficult to interpret in the newborn period because of immature kidney function.

●Magnetic resonance imaging (MRI) renography can be used to diagnose UPJ obstruction (image 5). The advantage of MRI is the ability to discern accurate anatomy defining the point of obstruction. MRI can also determine the split function of the kidney and simulate the diuretic renogram by providing washout data. The disadvantage of MRI is the cost and the need for general anesthesia and/or sedation in infants and small children [13-15]. In an observational study, a feed and wrap technique allowed MRI (without contrast) imaging without anesthesia in infants three months or younger [16]. The swaddle MRI technique only allows for anatomical assessment since an IV contrast is not administered; therefore, split function and washout date are not obtained.

If the infant has persistent postnatal hydronephrosis that is not severe (RPD <15 mm), a follow-up ultrasound is performed at three months of age to monitor the degree of hydronephrosis. If dilatation progresses to the threshold of RPD ≥15 mm, a diuretic renography should be obtained at that time to determine the relative function of the affected kidney and the presence of UPJ obstruction or other causes of obstructive uropathy. (See 'Asymptomatic patients' below.)

Older children — Older children most often present when they are evaluated for abdominal pain.

●CT scan may reveal a previously unsuspected intermittent UPJ in children that present emergently with acute and severe abdominal pain.

●Sonographic evaluation performed for children with abdominal pain including recurrent pain may demonstrate significant hydronephrosis.

The diagnosis of intermittent UPJ obstruction is confirmed if hydronephrosis is present on CT scan or sonogram when the child is symptomatic and resolves or greatly improves on follow-up sonogram when the child is well.

We do not routinely perform diuretic renal scan or MRI in patients with classic intermittent obstruction based on CT or sonogram finding unless we are concerned about decreased split renal function based on thinning of the renal parenchyma on the affected side.

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of UPJ obstruction includes other causes of hydronephrosis. Imaging studies (eg, diuretic renography, serial ultrasounds, and voiding cystourethrogram [VCUG]) differentiate UPJ obstruction from the following conditions:

●Vesicoureteral reflux (VUR). (See "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux".)

●Transient hydronephrosis. (See "Fetal hydronephrosis: Etiology and prenatal management", section on 'Transient hydronephrosis'.)

●Functional hydronephrosis.

●Other urological anomalies, including posterior urethral valves, congenital megaureter, ureterocele, ectopic ureters and multicystic dysplastic kidney (MCDK). (See "Primary megaureter in infants and children" and "Clinical presentation and diagnosis of posterior urethral valves", section on 'Diagnosis' and "Ureterocele", section on 'Diagnosis and evaluation' and "Kidney cystic diseases in children" and "Kidney cystic diseases in children", section on 'Multicystic dysplastic kidney'.)

MANAGEMENT

Goal — The goal of management is to preserve kidney function and avoid unnecessary surgery. There are no randomized trials that provide evidence for the optimal management of congenital UPJ obstruction. The following discussion is based upon observational studies, and the experience and opinions of experts in the field including the author.

Management approach

Prenatal — Prenatal intervention or early delivery is usually not necessary for fetal hydronephrosis including cases due to UPJ obstruction. There is no evidence that prenatal intervention in infants with either a single obstructed kidney or bilateral involvement improves kidney outcome. Possible exception is the rare situation when prenatal decompression of an enormously dilated renal pelvis is necessary to prevent dystocia or pulmonary compression. However, antenatal surgery should only be considered in the rarest of cases and only in select centers with expertise after a complete evaluation is performed. The criteria and setting for antenatal surgery are discussed in detail separately. (See "Fetal hydronephrosis: Etiology and prenatal management", section on 'Fetal surgery'.)

Symptomatic patients — Children who are symptomatic usually require operative intervention. If radiographic evaluation (CT scan or sonogram) reveals hydronephrosis during pain that resolves when symptoms subside, surgical intervention is warranted. As noted, we do not routinely perform diuretic renal scan or MRI in patients with classic intermittent obstruction based on CT or sonogram finding unless we are concerned about decreased split renal function based on thinning of the renal parenchyma on the affected side.

Additional management decisions involve treating concomitant conditions that can occur in symptomatic patients:

●Pyelonephritis – Rarely patients with UPJ obstruction will present with acute pyelonephritis and require intravenous antibiotics. Surgical repair is performed when the infection has resolved. If pyelonephritis does not respond to antibiotics and persistent infection is suggested on sonography, a temporary percutaneous pyelostomy tube should be placed to relieve the obstruction.

●Kidney stones – Kidney stones sometimes develop in the obstructed renal pelvis. Treatment involves removal of the stone at the time of surgical repair.

Asymptomatic patients — Most asymptomatic patients are infants who initially present prenatally (see 'Infants' above). Managing these infants is challenging because the natural course of UPJ obstruction is variable. It appears that many patients will have stable kidney function and improvement in the degree of hydronephrosis during long periods of observation, while others will have deterioration of their kidney function, and appear to benefit from surgical correction [17-19]. As a result, there is no reliable method to predict whether the function of a kidney with UPJ obstruction will remain unaffected or deteriorate with time and limited guidance on deciding between the management options of immediate surgical correction (ie, pyeloplasty) and observation with a later option of pyeloplasty dependent on the course of the obstruction.

In our center, the following approach based on postnatal ultrasound measurement of renal pelvic diameter (RPD) and the results of a diuretic renal scan is used to manage asymptomatic patients with UPJ-type hydronephrosis detected by antenatal ultrasound. Based on available literature and expert opinion, we believe that this approach best meets the goal of preserving kidney function while avoiding unnecessary surgery. We typically begin with observation of patients with asymptomatic UPJ obstruction and reserve surgical intervention for those patients with impaired or decreased function of the affected kidney, development of symptoms, increasing hydronephrosis, or parental/caregiver preference.

●RPD >15 mm and diuretic renal scan – For infants with RPD >15 mm on postnatal ultrasound, management is based on the results of the diuretic renal scan obtained between six and eight weeks of age:

•If the hydronephrotic kidney has decreased kidney function (less than 40 percent of split kidney function) compared with its normal contralateral mate, we recommend surgical intervention. Of note, relative kidney function may not be a reliable measure in patients with bilateral involvement. In patients with bilateral disease, glomerular filtration rate can be measured with serum creatinine and/or by renal scan. If kidney function is significantly decreased, surgery is indicated to relieve obstruction.

•If the hydronephrotic kidney has equal function compared with the normal contralateral kidney, we continue conservative management with observation and monitoring. A repeat sonogram is obtained in four to six weeks.

-If the subsequent sonogram shows no change or improvement, we continue to follow with serial ultrasounds. Renal ultrasound examinations are performed every four months until the child reaches one year of age, every six months for the next two years, and then annually for life.

If serial sonograms continue to show persistent hydronephrosis without substantial change from previous studies, we offer the family either continued observation, which will require ongoing monitoring with sonograms and possible diuretic renography, or surgical intervention.

-If hydronephrosis worsens, we repeat a diuretic renal scan. Surgical correction is recommended if the renal scan shows the affected kidney has a functional deterioration of >10 percent or has reached a threshold of less than 40 percent of split kidney function [19]. If kidney function remains stable, we offer the family either continued observation, which will require ongoing monitoring with sonograms and possible diuretic renography, or surgical intervention.

●RPD ≤15 mm – For infants with RPD ≤ 15 mm postnatal ultrasound, we observe and monitor these patients with ultrasound examination beginning at three months of age and every four to six months in the first year of life, then every 12 to 18 months thereafter until improvement to less than 10 mm. If there is an increase in the degree of hydronephrosis, diuretic renography is performed. If the affected kidney has less than 40 percent of split kidney function, or there is a serial loss greater than 10 percent from a previous study, surgical intervention is recommended.

Of note, in our practice, the washout curve or half-life calculation is not typically used to determine the need for surgery in any of these patients; however, others use a delay in delayed washout time (transit time of tracer from the renal pelvis) as an indicator for obstruction that warrants surgical correction [20].

Our approach may prevent unnecessary surgery in some asymptomatic patients and is supported by findings from several case series including the following large case series [17-19,21-24]:

●A single center retrospective study of 343 children with UPJ obstruction from 1988 to 2003 detected by antenatal ultrasound reported that 52 percent of patients underwent surgical correction [24]. The most common indication for surgical intervention was renal deterioration of greater than 5 percent. In this cohort of patients, 235 patients had initial relative kidney function (RRF) >40 percent, 68 had RRF between 30 and 40 percent, and 40 had RRF <40 percent. Initial RRF <40 percent and initial grade III and IV hydronephrosis were independent predictors for surgery.

●In a single center retrospective case series of 116 patients with grade III to IV hydronephrosis and obstructive diuretic renograms including 83 patients who were identified by antenatal ultrasound, treatment was divided into observation (n = 37), immediate pyeloplasty (n = 32), or pyeloplasty after observation (n = 47) [17]. The choice of therapy was based on ultrasound determination of grade of hydronephrosis and degree of parenchymal thinning, and kidney function on renal scan. Of the 37 patients managed by observation alone, kidney function remained stable and severity of hydronephrosis improved in 29 patients.

However, others in the field advocate that surgical intervention should be performed early so that kidney function may be preserved or improved with correction of the blockage [25,26].

Antibiotic prophylaxis — Although antibiotic prophylaxis has been recommended because urinary stasis is believed to be a risk factor for urinary tract infection (UTI), it does not appear that it is beneficial in the majority of children with UPJ obstruction. In our practice, antibiotic prophylaxis is given in patients with severe, grade IV hydronephrosis (>30 mm renal pelvis diameter) until the time of the surgical reconstruction. We also treat physiologic phimosis in boys with local steroid ointment:

●In one study of 92 children with severe hydronephrosis secondary to UPJ obstruction who were not treated with antibiotic prophylaxis, UTI occurred in 4.3 percent of the patients after a mean follow-up time of 27 months [27]. The mean age at the time of UTI was 6.1 months. All four patients with UTI presented with fever, and one developed urosepsis. The authors concluded that antibiotic prophylaxis was not beneficial in patients with severe UPJ obstruction.

●In a Turkish prospective study, there were no UTIs or evidence of renal scarring based on dimercaptosuccinate renography in 84 infants with UPJ obstruction who were not treated with prophylactic antibiotics at the end of one year follow-up [28].

Surgery

Indications — In our center, surgical intervention is performed for the following indications:

●Symptoms including pain, infection, and kidney stones.

●Increasing grade of hydronephrosis based on sonogram and decrease in function of the affected kidney defined as less than the threshold of 40 percent of split kidney function, or a serial loss greater than 10 percent based on diuretic renogram.

●Parental/caregiver or patient preference to avoid continued invasive testing (diuretic renogram) and allow definitive correction of the problem.

●Massive hydronephrosis with a RPD >30 mm.

Surgical options — Pyeloplasty is performed and consists of resecting the atretic or stenotic segment, and reattaching the normal ureter to the renal pelvis, thereby relieving the obstruction. If the obstruction is due to an aberrant renal blood vessel, the UPJ is dismembered and repositioned anatomically above the blood vessel preventing further obstruction (picture 4 and image 2). In the rare case of ureteral polyp(s), the polyp(s) and abnormal ureter segment at the UPJ are resected and the uninvolved ureter reanastomosed to the renal pelvis (image 1).

Surgical options for pyeloplasty include:

●Open dismembered pyeloplasty – The standard surgical procedure is open dismembered pyeloplasty [7]. Outcomes are excellent, with resolution of the obstruction in 90 to 95 percent of cases, including newborns [29,30]. Ultrasound examination is repeated approximately four to six weeks after surgery. If the hydronephrosis does not improve, a diuretic renogram should be performed to assess for persistent obstruction and/or a loss of kidney function.

●Robotic-assisted and laparoscopic pyeloplasty – Robotic pyeloplasty is now routinely performed in children and infants (picture 4 and movie 3 and movie 4 and movie 2 and movie 1) [31-35]. Laparoscopic pyeloplasty is less commonly used but centers that use this technique have reported excellent short-term results [34-42]. In general, robotic and laparoscopic techniques are performed transperitoneal in contrast to retroperitoneal for open pyeloplasty. Robotic and laparoscopic techniques also typically require postoperative placement of internal JJ stents that are subsequently removed about six weeks after the initial surgery under general anesthesia, which increases the economic burden [43].

●Others – Alternative surgical techniques, such as percutaneous and retrograde endopyelotomy, have been used in adults and children. This technique is typically reserved for repeat surgical cases where it is known that a crossing vessel is not present [44].

Surgical outcome — Failure rate following surgical repair is low.

●This was illustrated by a case series of 455 children undergoing pyeloplasty between 2000 and 2010 at a single Canadian pediatric tertiary center that reported a failure rate of 5.9 percent [45]. Failure rates were similar for both open and laparoscopic procedures. Reintervention was performed in 27 cases for worsening hydronephrosis (n = 16), pain (n = 7), urosepsis (n = 2), and other causes (n = 2). Five patients required three additional procedures, and 14 had two reinterventions. The mean time to first reintervention was 19.3 months.

●In a study based on the Nationwide Inpatient Sample of 6006 children with UPJ obstruction who underwent surgical repair, approximately 17 percent of the cases were performed by minimally invasive pyeloplasty (MIP) [46]. There was no in-hospital morality overall. The lowest rate of complications was observed in patients with open pyeloplasty (OP) at centers that performed OP at a high volume (5.7 percent). Similar higher rates were noted in children who underwent MIP at either a high volume (11.7 percent) or low volume center (10.4 percent), and the highest complication rate was seen in children with OP at a center with low volume (16 percent). Groups differed significantly in terms of age, gender, race, comorbidity, insurance status, and median household income. A multivariate logistic regression analysis adjusting for these variables demonstrated postoperative complication rates were similar for patients with either OP or MIP at centers with high volume, but complications were higher at centers with low volume for both MIP and OP. Overall, MIP was associated with a shorter hospital stay than OP.

Postoperative follow-up — Renal ultrasonography is performed four to six weeks postoperatively. If the ultrasound shows improvement (ie, decrease in the severity of hydronephrosis), the patient can then be followed by repeat ultrasound at increasing time intervals (ie, initially one year and then every five years until graduating high school) [47]. If the follow-up ultrasound does not show improvement, diuretic renography is performed to detect persistent obstruction, which may require an additional surgical procedure.

LONG-TERM OUTCOME — There are limited data on the long-term outcome of children with UPJ obstruction, which is confined to those who underwent open pyeloplasty. In one series of 49 postpubertal adolescents with antenatally diagnosed UPJ obstruction who underwent surgical repair at the average age of 4.7 months (range 1 to 17 months) between 1989 and 1992, relative kidney function improved from 37 percent preoperative to 43 percent after puberty [48]. There was also a decrease in time for isotope washout. Two patients (4 percent) required additional surgery for increasing hydronephrosis.

It remains unknown what proportion of patients with congenital UPJ obstruction who do not undergo surgical correction will become symptomatic as adults and/or require surgical intervention. It also is not known whether there is a difference in long-term kidney function between the observational and initial surgical approaches. It is clear that long-term follow up studies are needed to answer these questions so that optimal management decisions can be made.

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SUMMARY AND RECOMMENDATIONS

●Pathophysiology ‒ Ureteropelvic junction (UPJ) obstruction is a partial or total intermittent blockage of the flow of urine that occurs where the ureter enters the kidney, and results in hydronephrosis (figure 1 and picture 1). (See 'Pathophysiology' above.)

●Epidemiology ‒ UPJ obstruction is the most common pathologic cause of antenatally detected hydronephrosis with a reported incidence of up to 1 in 500 fetuses screened by antenatal ultrasound. (See 'Epidemiology' above.)

●Etiology ‒ Although the etiology of UPJ obstruction includes both congenital and acquired conditions, congenital causes are more common. Congenital UPJ obstruction is usually caused by intrinsic stenosis of the ureter at the ureteropelvic junction (picture 2), less commonly by an accessory renal artery crossing vessel causing extrinsic compression of the UPJ (picture 3), and rarely from an intraluminal ureteral polyp. (See 'Etiology' above.)

●Presentation ‒ Most cases of UPJ obstruction are diagnosed during the postnatal evaluation of prenatal hydronephrosis. In the absence of prenatal screening, infants may present with an abdominal mass (enlarged obstructed kidney), urinary tract infection (UTI), hematuria, or failure to thrive. In older children, the most common clinical manifestations of UPJ obstruction are intermittent flank and abdominal pain. Other presentations include kidney injury after experiencing minor trauma, hematuria, kidney stone, or rarely hypertension. (See 'Clinical presentation' above.)

●Diagnosis ‒ The diagnosis of UPJ obstruction is generally suspected when imaging studies (sonography or CT scan demonstrate hydronephrosis. The diagnosis is confirmed by diuretic renography. (See 'Diagnosis' above.)

●Differential diagnosis ‒ Imaging studies (eg, diuretic renography, serial ultrasounds, and voiding cystourethrogram [VCUG]) differentiate UPJ from other causes of hydronephrosis, including vesicoureteral reflux (VUR), transient and functional hydronephrosis, and other urological anomalies (eg, posterior urethral valves [PUV], congenital megaureter, ureterocele, ectopic ureters, and multicystic dysplastic kidney [MCDK]). (See 'Differential diagnosis' above.)

●Management

•Goal of management is to preserve kidney function, prevent pain, and avoid unnecessary surgery. (See 'Goal' above.)

•There are no randomized trials that provide evidence for the optimal management of congenital UPJ obstruction. The following management approaches are based upon observational data, and the experience and opinions of the author. (See 'Goal' above and 'Management approach' above.)

-Prenatal intervention or early delivery is usually unnecessary for fetal hydronephrosis, including for cases due to UPJ and contraindicated because of the risk of fetal demise. In extremely rare cases, decompression of an enormously dilated renal pelvis may be considered to prevent dystocia or fetal pulmonary compression. (See "Fetal hydronephrosis: Etiology and prenatal management", section on 'Fetal surgery'.)

-In symptomatic patients (typically older children and teenagers), we suggest surgical intervention to relieve the obstruction and resolve symptoms versus observation and ongoing monitoring (ie, serial ultrasounds and diuretic renal scans (Grade 2C). (See 'Symptomatic patients' above.)

-In asymptomatic patients with persistent significant unilateral UPJ obstruction (ie, renal pelvic diameter >15 mm on postnatal ultrasound), results of the diuretic renal scan are used to guide management decisions. (See 'Asymptomatic patients' above.)

For patients with impaired kidney function (ie, split kidney function less than 40 percent of the affected kidney on diuretic renal scan), we suggest surgical correction versus observation and monitoring (Grade 2C).

For patients with equivalent function of the two kidneys (ie, split kidney function greater than 40 percent of the affected kidney on diuretic renal scan), we suggest observation and monitoring (ie, serial ultrasounds and diuretic renal scans) versus immediate surgical correction (Grade 2C). In our center, indications for subsequent surgical intervention include increasing hydronephrosis or massive hydronephrosis with a renal pelvic diameter (RPD) greater than 30 mm on subsequent ultrasound, decrease in split kidney function below 40 percent or a serial loss greater than 10 percent in subsequent renal scans, the development of symptoms, and/or parental and patient preference (avoiding serial diuretic renograms).

●Outcome ‒ Outcome data following surgical correction demonstrate a rate of recurrent obstruction requiring additional intervention is <5 percent. Long-term data on patients regarding kidney function are not available for those managed by observation alone and limited data for those with pyeloplasty that suggest slight improvement in kidney function and degree of obstruction. (See 'Long-term outcome' above and 'Surgical outcome' above.)