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]. The goal is to identify which patients with UPJ-type hydronephrosis have obstruction. UPJ obstruction is the most common anatomical cause of antenatal hydronephrosis.

UPJ obstruction is more common among boys than girls and on the left rather than right side [3,4]. The reported rate of bilateral involvement is approximately 10 percent [1,4].

PATHOPHYSIOLOGY — 

UPJ obstruction is caused by congenital anomalies or acquired lesions that restrict urinary flow across the UPJ, resulting in hydronephrosis (figure 1) [1]. Most cases are thought to be due to partial obstruction because complete obstruction would result in rapid deterioration of kidney function. 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

●Degree of compliance of the renal pelvis (ie, ability to stretch)

The renal pelvis 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 pelvis are less vulnerable to damage from obstruction than those with a small pelvis, especially during diuresis.

ETIOLOGY — 

UPJ obstruction in children can be caused by:

●Intrinsic narrowing – Most cases of UPJ obstruction are caused by intrinsic narrowing, in which the ureter is narrowed at the UPJ and kinked or tethered by normal connective tissue as the ureter enters the pelvis, resulting in obstruction of urinary flow (picture 1 and movie 1).

●Crossing vessel – In approximately 10 percent of pediatric UPJ obstructions, an aberrant or accessory renal vessel arises from the lower pole of the kidney, resulting in intermittent compression of the UPJ and blockage of urinary flow (image 1 and picture 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.

●High insertion – In a small number of patients, there may be a high insertion of the ureter into the renal pelvis without intrinsic narrowing that results in UPJ obstruction (movie 3).

●Ureteral polyps – Less than 1 percent of pediatric UPJ obstructions are caused by an acquired intraluminal ureteral polyp(s) (image 2 and movie 4) 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.

If surgical correction is deemed appropriate, preoperative determination of the underlying cause is not absolutely necessary, because the reconstruction technique is similar regardless of UPJ etiology. The exact etiology and operative plan can be determined intraoperatively.

CLINICAL PRESENTATION

●Infants

•Prenatal hydronephrosis – In geographic areas where prenatal ultrasound screening is routinely performed, most cases of UPJ obstruction are identified by the finding of hydronephrosis on prenatal ultrasound. The diagnosis of UPJ obstruction is made in the postnatal period with follow-up ultrasound (image 3) and subsequent diuretic renal scan to differentiate between UPJ hydronephrosis versus UPJ obstruction requiring surgery [5]. (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 (UTI), 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 flank pain or abdominal pain (referred to as Dietl crisis). The pain may worsen during brisk diuresis (eg, after consumption of caffeine). The symptoms are often intermittent but may be acute and severe. The pain may be accompanied by nausea and vomiting, leading to an evaluation of the gastrointestinal tract [6]. Imaging findings consistent with UPJ obstruction are unilateral hydronephrosis without ureteral dilation, especially if the imaging abnormalities coincide with the symptoms. (See 'Diagnosis' below.)

Children may also present with hematuria, kidney stones, acute pyelonephritis, or hypertension [6-8]. Others present with kidney injury after experiencing minor trauma because the kidney with UPJ-type hydronephrosis is more susceptible to damage from trauma [9].

UPJ obstruction may also present as an incidental finding on ultrasound for other conditions (image 3) or as a finding on 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 identified during an evaluation for other genitourinary anomalies, such as a horseshoe kidney [10], or a syndrome such as CHARGE (coloboma, heart anomaly, choanal atresia, retardation, genital and ear anomalies) [11]. In patients with a horseshoe kidney, the obstruction is usually due to intrinsic narrowing of the UPJ and is usually on the left side (movie 5).

DIAGNOSIS

●Infants – UPJ obstruction usually comes to attention when hydronephrosis is detected on prenatal ultrasound. UPJ obstruction is the most common cause of antenatal hydronephrosis. The diagnosis is confirmed if the postnatal ultrasound shows characteristic features of UPJ obstruction (image 3 and algorithm 1):

•Unilateral hydronephrosis (dilation of the renal calyx and pelvis)

•No dilation of the ureters or bladder

•Normal contralateral kidney

Male infants with bilateral UPJ-type hydronephrosis should be evaluated for posterior urethral valves and vesicoureteral reflux with a voiding cystourethrogram (VCUG). If the VCUG is normal, postnatal management can proceed in similar fashion to unilateral UPJ hydronephrosis. 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".)

Subsequent evaluation and management depend on the degree of hydronephrosis on the postnatal ultrasound, as outlined below.

●Older children – Older children with UPJ obstruction more commonly present with flank pain or abdominal pain, which may be intermittent but can be acute and severe (see 'Clinical presentation' above). In this age group, UPJ obstruction is often caused by a crossing vessel that impinges upon the renal pelvis due to somatic growth and changing anatomic relationships.

The diagnosis is suspected based on the presenting symptoms and confirmed by imaging (kidney ultrasound (image 3) or CT scan (image 2)) that shows:

•Unilateral hydronephrosis

•No dilation of the ureter or bladder

•The hydronephrosis resolves or greatly improves on follow-up imaging when the child is well

DIFFERENTIAL DIAGNOSIS — 

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

●Primary vesicoureteral reflux – Characterized by dilatation of the upper collecting system (hydronephrosis and ureteral dilatation, typically unilateral) with no bladder dilatation or bladder wall thickening. The vesicoureteral reflux is confirmed by VCUG. (See "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux".)

●Transient hydronephrosis – Prenatal dilation of the renal pelvis that resolves over time and is not clinically significant. (See "Fetal hydronephrosis: Etiology and prenatal management", section on 'Transient hydronephrosis'.)

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

FURTHER EVALUATION

Infants

Severe hydronephrosis — For infants with severe hydronephrosis (renal pelvic diameter (RPD) >15 mm) and parenchymal thinning (grade 4 in the Society for Fetal Urology [SFU] classification), we perform further evaluation with a diuretic renal scan at six to eight weeks of age to evaluate the severity of the obstruction and assess kidney function (algorithm 1).

●Diuretic renal scan – In our center, a diuretic renal scan is used to confirm and further evaluate UPJ obstruction and other causes of obstructive uropathy.

This test consists of renal scan following administration of a diuretic (typically furosemide). The preferred radioisotope is technetium-99m-mercaptoacetyltriglycine (Tc-99m MAG3), which is taken up by the kidney cortex, filtered across the glomerular basement membrane 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), which correlates with the degree of obstruction. It also assesses kidney function, which is reported as the percent relative function of each kidney (known as split kidney function or differential renal function). (See "Postnatal evaluation and management of hydronephrosis", section on 'Diuretic renography'.)

In general, clinically significant obstruction is indicated by either:

•Prolonged washout – A half-life >20 minutes, indicating delayed transient time of the TC-99m isotope from the kidney.

•Impaired kidney function – Affected kidney with <40 percent of total kidney function (eg, >60 percent on the right and <40 percent on the left)s or >10 percent decline in function of the affected kidney from baseline on serial scans (if performed).

Infants with both of these findings generally should proceed to surgery. If relative kidney function is preserved on the involved side, the child may be observed with a follow-up diuretic renal scan three to four months later to assess for improvement in drainage. Those with persistent hydronephrosis but normal findings or mild abnormalities on diuretic renal scan require serial monitoring. (See 'Surgery' below and 'Asymptomatic patients' below.)

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

●MRI renography – Alternatively, MRI renography can be used for further evaluation of UPJ obstruction (image 5). The advantage of MRI over diuretic renogram is the ability to define the anatomy of the UPJ obstruction. MRI can also determine the split function of the kidney and simulate the diuretic renal scan by providing washout data, although the software required for this analysis is complex and costly. The disadvantages of MRI are the cost and the need for general anesthesia and/or sedation in infants and small children [12-14]. However, for young infants, an MRI can also be performed without sedation or anesthesia, using a swaddle technique. In an observational study, this technique allowed MRI imaging without anesthesia in infants three months or younger [15]. A limitation of the swaddle MRI technique is that it does not include intravenous contrast and therefore only allows for anatomical assessment and does not provide data on washout or split kidney function.

Nonsevere hydronephrosis — If the infant has persistent postnatal UPJ-type hydronephrosis that is not severe (RPD <15 mm, SFU grades 3 or less), we perform a follow-up ultrasound at three months of age to monitor the degree of hydronephrosis. We do not routinely perform diuretic renal scan for nonsevere UPJ-type hydronephrosis as long as the hydronephrosis does not worsen.

If dilatation progresses to the threshold of RPD ≥15 mm or increases to SFU grade 4, we generally perform a diuretic renal scan to determine the relative function of the affected kidney and to confirm the presence of UPJ obstruction versus other causes of obstructive uropathy. (See 'Asymptomatic patients' below.)

Older children — For children with classic intermittent pain due to obstruction confirmed by CT or sonogram and no other abnormalities, these findings are sufficient indications for surgery. Prior to surgery, we assess kidney function to ensure that the kidney is worth salvaging; this can be done by reviewing the CT scan (the presence of contrast in the kidney and normal renal parenchyma suggest adequate function) or by performing a diuretic renal scan. (See 'Surgery' below.)

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 on observational studies and the experience and opinions of experts in the field including the author.

Prenatal management — 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.

Very rarely, for a fetus with massive hydronephrosis, prenatal decompression may be considered 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'.)

Postnatal management

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 and difficult to predict. Many children 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 [16-18]. There is no reliable method to predict changes in kidney function over time. Only limited evidence is available to guide decisions about timing of surgical correction (ie, pyeloplasty) versus observation with the option of later pyeloplasty if the condition does not improve.

In our center, we use the following approach to manage asymptomatic patients with UPJ-type hydronephrosis detected by antenatal ultrasound (algorithm 1). The decision to proceed with pyeloplasty is based on the severity of hydronephrosis on postnatal ultrasound and the results of a diuretic renal scan. 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.

●Massive hydronephrosis – If the postnatal ultrasound shows massive hydronephrosis (renal pelvic diameter [RPD] ≥30 mm), we recommend surgery regardless of symptoms. However, we do perform a diuretic renal scan to measure baseline kidney function. (See 'Indications' below and 'Severe hydronephrosis' above.)

●Severe hydronephrosis – If the postnatal ultrasound shows severe hydronephrosis (RPD >15 to 30 mm) and parenchymal thinning (Society for Fetal Urology [SFU] grade 4), we perform a diuretic renal scan between six and eight weeks of age (see 'Severe hydronephrosis' above). For patients with no parenchymal thinning (SFU grade 3) and RPD >15, we monitor with serial sonograms and typically proceed to a diuretic renogram if the hydronephrosis worsens.

Management depends on the result of the diuretic renal scan, as follows:

•Decreased split kidney function – If the hydronephrotic kidney has decreased kidney function relative to the contralateral kidney (eg, hydronephrotic kidney contributes less than 40 percent of total kidney function), we recommend surgical intervention. Of note, relative kidney function (RKF) 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.

•Equal split kidney function – If the hydronephrotic kidney has approximately 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 kidney ultrasounds. The ultrasound examinations are performed every four months until the child reaches one year of age, then every six months until three years of age, and then annually for life.

If serial ultrasounds 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 renal scans) or surgical intervention.

-If hydronephrosis worsens, we repeat a diuretic renal scan.

-Surgical correction is recommended if the renal scan shows that the affected kidney has a functional deterioration of >10 percent or has reached a threshold of less than 40 percent of split kidney function [18]. If kidney function remains stable, we offer the family either continued observation (which will require ongoing monitoring with sonograms and possible diuretic renal scans) or surgical intervention.

Of note, in our practice, we do not routinely use the washout curve or half-life calculation from the diuretic renal scan to determine the need for surgery in any of these patients. By contrast, some other experts use a delay in delayed washout time (transit time of tracer from the renal pelvis) as an indicator for obstruction that warrants surgical correction [19].

●Nonsevere hydronephrosis – If the postnatal ultrasound shows hydronephrosis that is not severe (RPD <15 mm and no parenchymal thinning [ie, SFU grade 2 or 3]), we use a watchful waiting approach. We 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 or if parenchymal thinning develops (SFU grade 4), we perform a diuretic renal scan. If the scan shows that 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, we suggest surgical intervention.

●Evidence – The approach to asymptomatic patients outlined above is designed to meet the goal of preserving kidney function while avoiding unnecessary surgery. It is supported by the following large case series [16-18,20-23]:

•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 [23]. The most common indication for surgical intervention was kidney function deterioration of greater than 5 percent. In this cohort of patients, 235 patients had initial RKF >40 percent, 68 had RKF between 30 and 40 percent, and 40 had RKF <40 percent. Initial RKF <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) [16]. The choice of therapy was based on ultrasound determination of grade of hydronephrosis and degree of parenchymal thinning, as well as 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 [24,25].

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 kidney function based on thinning of the kidney 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 nephrostomy 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.

Antibiotic prophylaxis — In our practice, we do not give antibiotic prophylaxis to children with classic UPJ obstruction, provided that the RPD is <30 mm, because prophylaxis is not beneficial for most children with UPJ obstruction. We reserve antibiotic prophylaxis for patients with severe, grade IV hydronephrosis (RPD ≥30 mm) and continue this until the time of the surgical reconstruction.

Evidence for this limited approach to antibiotic prophylaxis includes these studies:

●In one study of 92 children with severe hydronephrosis secondary to UPJ obstruction who were not treated with antibiotic prophylaxis, urinary tract infection (UTI) occurred in 4.3 percent of the patients after a mean follow-up time of 27 months [26]. 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 kidney 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 [27].

Surgery

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

●Children with symptoms or complications of UPJ obstruction, including pain, infection, and kidney stones. (See 'Symptomatic patients' above.)

●Massive hydronephrosis (RPD ≥30 mm).

●Asymptomatic infants and children with severe hydronephrosis (RPD >15 mm or increasing) and decrease in function of the affected kidney on diuretic renal scan (affected kidney contributes <40 percent of total kidney function or >10 percent decrease in kidney function compared with baseline). (See 'Asymptomatic patients' above.)

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

Operative technique — The pyeloplasty procedure depends on the cause of the UPJ obstruction:

●Intrinsic narrowing – If the UPJ obstruction is due to an intrinsic narrowing, the repair consists of exposing the dilated renal pelvis (picture 1 and movie 1), resecting any tethering connective tissue (movie 6 and movie 7), resecting the narrowed segment (movie 8), and reattaching the normal ureter to the renal pelvis (movie 9), thereby relieving the obstruction.

●Crossing vessel – If the obstruction is due to an aberrant crossing renal blood vessel, the UPJ is dismembered and repositioned anatomically above the blood vessel, thus preventing recurrent obstruction (image 1 and picture 2 and movie 2).

●High insertion – If the obstruction is due to a high insertion, the UPJ is exposed and excised and the normal ureter reanastomosed to a dependent position in the renal pelvis, approximately 1 cm from the lower pole kidney parenchyma (movie 3).

●Polyps – In the rare case of ureteral polyp(s), the polyp(s) and abnormal ureter segment at the site of the polyp are resected and the uninvolved ureter reanastomosed to the renal pelvis (movie 4). If the polyp is completely resected, it rarely recurs.

Surgical options for pyeloplasty include:

●Open pyeloplasty – The traditional surgical procedure is open pyeloplasty, where the abnormal UPJ and ureter are resected and the normal ureter reanastomosed to the renal pelvis (dismembered pyeloplasty). Outcomes are excellent, with resolution of the obstruction in 90 to 95 percent of cases, including newborns [28,29].

Ultrasound examination is repeated approximately four to six weeks after surgery. If the hydronephrosis is not stable or improved, a diuretic renal scan should be performed to assess for persistent obstruction and/or a loss of kidney function.

●Robotic-assisted and laparoscopic pyeloplasty – Robotic-assisted pyeloplasty is now routinely performed in children and infants (picture 3 and movie 10 and movie 8 and movie 9 and movie 2) [30-34]. Laparoscopic pyeloplasty is less commonly used, but centers that use this technique have reported excellent short-term results [33-41]. In general, robotic and laparoscopic techniques are performed from a transperitoneal approach (in contrast with the retroperitoneal approach for open pyeloplasty).

Robotic and laparoscopic techniques also typically require postoperative placement of an internal JJ stent (picture 3 and movie 9) that is subsequently removed about six weeks after the initial surgery (movie 11). This requires general anesthesia, which increases the economic burden [42].

Surgical outcome — Outcomes following surgical repair of UPJ obstruction are generally excellent. 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 (defined as a need for surgical reintervention other than stent removal) [43]. 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. Failure rates were similar for both open and laparoscopic procedures.

Compared with open pyeloplasty, minimally invasive techniques (laparoscopic or robot-assisted surgery) have slightly higher operative success rates (>95 percent), with slightly longer operating times, shorter length of stay, and, possibly, fewer postoperative complications [28,44]. Compared with laparoscopic pyeloplasty, robot-assisted surgery may have slightly higher short-term success rates, fewer complications, and shorter length of stay [45]. For infants and children <2 years, success rates are also high for each of these techniques, with no significant differences in complications [45,46].

Postoperative follow-up — The JJ stent is removed approximately six weeks after the UPJ repair during an outpatient cystoscopy procedure (movie 11).

Kidney ultrasound is performed four to six weeks later (ie, approximately 10 to 12 weeks after UPJ repair). 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 late adolescence) [47]. If the follow-up ultrasound shows no improvement or increased hydronephrosis, a diuretic renal scan is performed to detect persistent obstruction, which may require an additional surgical procedure.

Management also includes treatment of physiologic phimosis, if present, because this may contribute to the risk of urinary tract infection.

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.

INFORMATION FOR PATIENTS — 

UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Hydronephrosis in babies (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Pathophysiology and epidemiology ‒ Ureteropelvic junction (UPJ) obstruction is a partial or total intermittent blockage of urine flow that occurs where the ureter enters the kidney, resulting in hydronephrosis (figure 1 and picture 1). It is the most common pathologic cause of antenatally detected hydronephrosis. (See 'Pathophysiology' above and 'Epidemiology' above.)

●Etiology ‒ Congenital UPJ obstruction is usually caused by intrinsic narrowing of the ureter at the UPJ (movie 1), less commonly by an accessory renal artery crossing vessel causing extrinsic compression of the UPJ (movie 2) or high insertion of the ureter (movie 3), and, rarely, by an intraluminal ureteral polyp (movie 4). (See 'Etiology' above.)

●Presentation ‒ Most cases of UPJ obstruction come to attention due to hydronephrosis on prenatal ultrasound, and the diagnosis is confirmed on postnatal follow-up ultrasound. Infants who are not diagnosed prenatally 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 made when imaging studies (sonography or CT scan) demonstrate unilateral hydronephrosis with no dilation of the ureter or bladder. Other findings require additional evaluation for other causes of hydronephrosis, including vesicoureteral reflux, megaureter, or posterior urethral valves. (See 'Diagnosis' above and 'Differential diagnosis' above.)

●Further evaluation – If the hydronephrosis is severe, further evaluation for infants includes a diuretic renal scan to confirm the diagnosis and assess kidney function (algorithm 1). For older children with typical clinical presentation and imaging findings of UPJ obstruction, a diuretic renal scan is often unnecessary. (See 'Further evaluation' above.)

●Management

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

-Impaired kidney function – For those with impaired kidney function on diuretic renal scan (ie, the affected kidney contributes <40 percent of total kidney function) or massive hydronephrosis (RPD ≥30 mm), we suggest surgical correction versus observation and monitoring (Grade 2C).

-Normal kidney function – For those with equivalent function of the two kidneys (ie, the affected kidney contributes ≥40 percent of kidney function), we suggest observation and monitoring (ie, serial ultrasounds and diuretic renal scans) rather than immediate surgical correction (Grade 2C). Indications for subsequent surgical intervention include development of symptoms, subsequent ultrasound showing massive hydronephrosis (RPD ≥30 mm) or increasing hydronephrosis, or renal scans showing decrease in kidney function.

-Limited role for antibiotic prophylaxis – For infants and children with classic unilateral UPJ obstruction and RPD <30 mm, we suggest not giving antibiotic prophylaxis (Grade 2C). We reserve antibiotic prophylaxis for patients with severe, grade IV hydronephrosis (RPD ≥30 mm) and continue this until the time of the surgical reconstruction. (See 'Antibiotic prophylaxis' above.)

•Symptomatic – For patients with symptoms or complications of UPJ obstruction, such as pain, infection, and kidney stones (typically older children and adolescents), we suggest surgical intervention to relieve the obstruction and resolve symptoms rather than observation and ongoing monitoring (Grade 2C). (See 'Symptomatic patients' above.)

•Technique – Surgery usually involves resection of the obstruction and reanastomosis of the ureter to the renal pelvis (picture 3). (See 'Operative technique' above.)

●Outcome ‒ Following surgical correction, approximately 5 percent of patients develop recurrent obstruction requiring additional intervention. Limited data suggest slight improvement in kidney function in long-term follow-up. (See 'Surgical outcome' above and 'Long-term outcome' above.)