AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Ureteropelvic junction (UPJ) obstruction is by far the most common cause of pediatric hydronephrosis, occurring in 1 per 1000-2000 newborns. Widespread use of antenatal ultrasonography and the advent of modern imaging techniques have resulted in earlier and more common diagnosis of hydronephrosis. In the late 1800s, Trendelenburg performed the first reconstruction of an obstructed kidney rather than simple nephrectomy. Most early repairs consisted of a longitudinal incision through the narrow segment to be closed in a horizontal fashion. In 1891, Kuster successfully repaired a UPJ obstruction by ligating the renal pelvis below the obstruction and transposing the upper ureter to the renal pelvis with a side-to-side anastomosis.

The landmark development was the intravenous pyelography (IVP) developed by Swick in 1929, which actually visualized the site of obstruction. In 1936, Foley described the results of 20 pyeloplasties using YV repair. In 1946, Anderson and Hynes published their experience with an operation that included the complete transection of the upper ureter, subsequent spatulation of the ureter, and trimming of the redundant pelvis. This highly successful technique has become the criterion standard of surgical repair used today. Since then, an explosion of information has been available relating directly to the pathogenesis, diagnosis, and treatment of UPJ obstruction.

History of the Procedure

Before the advent of ultrasonography, the most common presenting symptom was pain, which was reported by approximately 50% of patients; urinary tract infection (UTI) was the second most common presentation reported, followed by hematuria. Other symptoms included abdominal masses and GI discomfort. Most patients were children, and only 25% of those with a diagnosis of UPJ obstruction were younger than 1 year. Of those infants, almost half had an abdominal mass. Approximately 50% of all abdominal masses were renal in origin, and 40% of them were associated with UPJ obstruction.

Problem

UPJ obstruction is by far the most common cause of pediatric hydronephrosis. As antenatal ultrasonography has become more popular, fetal and neonatal hydronephrosis and UPJ obstruction are found more frequently; therefore, the management of pediatric UPJ obstruction remains more important. Choosing an optimal therapeutic regimen is difficult due to the high variability in function, degree of obstruction, extent of damage, and potential for regeneration in growing kidneys.

Frequency

Obstruction occurs more commonly in boys than in girls, especially in the newborn period, when the ratio exceeds 2:1. Left-sided lesions predominate, particularly in the neonate, up to approximately 67%, and bilateral cases are observed in 10-40% of cases; however, fewer than 5% of patients require bilateral repair. This propensity of bilateral occurrence may explain the frequent coexistence of UPJ obstruction and multicystic dysplasia. One theory attributes multicystic dysplasia to complete obstruction of the upper ureter, and kidneys that are affected simply have UPJs with total occlusion of the upper ureter.

Etiology

Intrinsic abnormalities

In the embryogenesis, the UPJ is formed during the fifth week. By weeks 10-12 of gestation, the initial tubular lumen of the ureteric bud becomes recanalized, and the UPJ area is the last to recanalize. Inadequate canalization of this area is the main embryological explanation of UPJ obstruction. Several growth factors may control embryogenesis of UPJ. Researchers propose that improper innervation with diminished synaptic vesicles may be a factor in the development of UPJ obstruction, and factors involved in neuronal development, such as protein gene product (PGP) 9.5 (a general neuronal marker), S-100 protein (a nerve supporting cell marker), synaptophysin (a synapse vesical marker), and nerve growth factor receptor were all decreased in the resected specimens of UPJ.

The induction of kidney mesenchyme by the ureteric bud is mediated by a transcription factor Pax-2. Other factors, such as c-ret, kdn-1, and wt1, also may be involved. A well-known growth factor, transforming growth factor b (TGFb), may account for the abnormal smooth musculature in the obstructed renal pelvis. More research certainly is needed to clarify the molecular basis of the UPJ obstruction.

This intrinsic obstruction is evident as the ureteral narrowing with angulation is found. During exploration, the catheter usually is passed to the renal pelvis without resistance, and this is evidence of the fact that the true narrowing is not a main pathologic change in UPJ obstruction. Some claimed the presence of remnant valvular mucosal folds, while others postulate the disproportionate abundance of longitudinal muscles as the cause of this condition.
The most attractive theory is that the obstruction is secondary to muscular discontinuity, which disrupts the coordinated motion of smooth muscle cells and may result in impeded transport of urine and blockage of the downward transmission of ureteral peristalsis. This absence or disorientation of smooth muscle fibers at UPJ is clearly evident on electron microscope evaluation with the findings of hypotrophy/hypertrophy of the smooth muscle and its replacement with excessive collagen, combined with diminution of nerve terminals and nerves at the stenotic portion.

Extrinsic abnormalities

Extrinsic obstructions secondary to bands, kinks, and aberrant vessels also are commonly encountered. In 40% of cases, an aberrant, accessory, or early-branching lower pole segment vessel is found and observed to compress the ureter, causing mechanical obstruction. In this case, with the increased urine volume, the UPJ angulation with intrapelvic volume expansion causes increased resistance and obstruction. Further angulation may occur as it becomes adherent to an inflammatory process. The presence of such a vessel in the vicinity of UPJ has gained recent attention after the advent of the endourological management. The anterior surface of the renal pelvis is associated with a lower pole vessel in 65% of cases, whereas the posterior surface is in contact with a vessel in 6% of the kidneys examined. This information is relevant for the endoscopic incision of UPJ, making lateral incision the only safe option.

Patients with extrinsic obstructions present rather late in childhood, with intermittent abdominal or flank pain. Horseshoe or pelvic kidney, duplex collecting systems, and other rotational abnormalities also may cause UPJ obstruction. Cases of so-called high inserted ureter–to–renal pelvis exist, but this is presumed to be a secondary phenomenon to obstruction because the ureteral insertion seems to be higher in cases of dilated renal pelvis.

Pathophysiology

The urinary drainage from renal pelvis to ureter is determined by many factors. Urine volume and flow, the degree of UPJ obstruction, the functional capacity of glomerulus and collecting system, and the compliance of renal pelvis are the 4 main variables determining the pelvic pressure. At first, in response to the increased pelvic pressure, the renal pelvis dilates and ureteral muscles show hypertrophy. In the intrarenal type of obstruction, the degree of dilation is restricted by renal parenchyme; thus, the damage usually is more severe than the extrarenal type. Parenchymal damage by UPJ obstruction is well documented by histologic changes, which are more severe in cases of differential function of less than 35%.

Experimental studies using artificially made complete obstructions showed changes that suggest the upward transmission of ureteral pressure in an obstructed kidney and the subsequent effects on tubular pressure, tubular function, renal blood flow (RBF), and glomerular filtration rate (GFR). The urinary obstruction results in the impairment of all renal functions except urinary dilution; however, the elevation of ureteral pressure above a certain point had no further effect on intratubular pressure. With complete ureteral ligation, a rise in renal pelvic pressure occurs, which is only transitory; over a period of hours, the renal pelvic pressure falls in concert with RBF. Also, the intrapelvic pressure in patients with UPJ obstruction most often is in the normal range assessed at the time of surgery. Researchers propose that the expansion of the renal pelvis is protective by dampening out of the pressure.

Koff proposed the concept of pressure- or volume-dependent flow. In instances of intrinsic obstruction, at low urinary flow rates, no obstruction exists; however, as the flow rate increases, the urinary bolus are not conducted, causing the renal pelvis to distend. This concept is called a pressure-dependent flow pattern. On the contrary, in cases of extrinsic compression usually caused by aberrant vessels, urine flow is impeded only after a definite amount of urine is collected in the renal pelvis. This is an example of volume-dependent flow, and the pressure damage is only evident intermittently; thus, the degree of damage generally is less than that of intrinsic obstruction.

Experimental results show that the release of complete ureteral obstruction of 24 hours of duration results in a near-normal GFR, but the total number of filtering nephrons is decreased causing increase in the single nephron GFR. Local production of prostacyclin and prostaglandin E₂ (PGE2) seems to affect glomerular arteriolar resistance. Tubular functions also are changed by obstruction, but the effects of obstruction on distal tubular and collecting duct physiology may not be as quantitatively significant as the effect on deep nephron function.

Most clinically observed obstructions are partial, and the models of partial ureteral obstruction have been developed. In this case, the total GFR of the obstructed kidney is decreased, and an increase occurs in the single nephron GFR. This process probably is the result of changes in the local elaboration of vasoactive peptides and cytokines.

Significant urinary obstruction invariably results in tubular dilation, glomerulosclerosis, inflammation, and fibrosis. Although not absolute, a good correlation exists between the severity of these histologic changes and the function remaining in the affected kidneys. Sclerotic glomeruli and fibrosis are reliably localized to areas of the kidney that demonstrate the most inflammatory infiltrate. The infiltrate consists mostly of mononuclear cells in both the cortex and medulla. The cells predominantly are macrophages, though a small number of T cells are present.

Elevated levels of interleukin-5 (IL-5) and eotaxin-2 were demonstrated in a study, which suggested that chemokines produced by the urothelium may be the chemoattractants for leukocytes, leading to further inflammatory cell infiltration, mast cell migration, and activation. The arrival of the infiltrating cells closely corresponds with the decrease in RBF and GFR after obstruction. Obstructed kidneys also demonstrate increases in cyclooxygenase activity and increased thromboxane synthetase. The monocytic infiltration has a role in changing the eicosanoid elaboration in the kidney, which, in turn, acts locally to decrease the GFR.

The activation of the renin-angiotensin system is a major factor in partial obstruction. Administration of the angiotensin-converting enzyme (ACE) inhibitor enalapril not only maintained RBF in partially obstructed kidneys at 3 weeks postobstruction but also prevented the histologic changes of glomerulosclerosis. The effects of obstruction are not all ischemic. Obstruction can mimic renal artery stenosis, and, because of its intense vasoconstrictor action, the resulting increase in angiotensin II (AII) leads to decreases in GFR. It is becoming increasingly clear, however, that AII profoundly affects the expression of growth factors in the developing kidney that ultimately are responsible for the changes in the histology. Up regulation of TGFb is apparent in these infiltrating cells, and the degree of up regulation correlates directly with fibrosis and collagen deposition in obstructed kidneys.

The fibrosis and microscopic deterioration of the kidney can be prevented by administration of ACE inhibitors. Experiments suggest that AII has a central role in the development of tubulointerstitial fibrosis in obstructed kidneys, because its inhibition ameliorates the severity of the leukocytic infiltration, the impairment of RBF, and the severity of fibrosis in obstructed kidneys. Other growth factors also may be relevant. A series of experiments with fetal opossum showed that administration of insulinlike growth factor 1 (IGF-1) decreased the fibrosis in obstructed fetal kidneys. No single factor or cytokine is responsible for the changes found in obstructed kidneys; however, continued investigation to prevent renal damage with medical treatment during the period of observation.

Clinical

Until the 1980s the most important study was IVP. Oestling folds, which resemble UPJ obstruction, are remnants of fetal renal development. No significant renal pelvic dilation or hydronephrosis is associated with this condition; however, most hydronephrotic kidneys currently are detected prenatally.

UPJ obstruction is coexistent with other types of congenital abnormality in almost 50% of patients, and 10% of patients with UPJ obstruction show ipsilateral reflux. Voiding cystourethrogram (VCUG) is well warranted. In such cases, more severe anomalies should be treated first. Some believe that simultaneous repair of both conditions is not recommended, while others have performed simultaneous repairs with good results. There also are incidences of both the ureteropelvic and the ureterovesical junctions. In these cases, UPJ obstruction should be treated first because most distal ureteral obstructions are not severe. Duplication anomalies usually cause UPJ obstruction at the lower poles. In these cases, suspicion of vesicoureteral reflux also should be heightened.

In older children, periodic abdominal pain with vomiting is a common symptom. These symptoms are probably caused by intermittent kinking of the UPJ. Episodic flank pain following a diuresis is a common presenting feature in young adults but is uncommon in children. Rare urothelial tumors, such as benign fibroepithelial polyp or urinary stones, can mimic UPJ obstruction in children. Although rarely observed in developed countries, massive dilation of the renal pelvis and kidney fills the entire flank and abdomen. UPJ obstruction is a major cause of this condition.

INDICATIONS

Section 3 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Upon diagnosis of a UPJ obstruction, prompt intervention is appropriate to prevent or minimize renal damage. First, prophylactic antibiotic therapy is warranted in cases of moderate-to-severe dilatations because any UTI, especially in the neonatal period, dramatically increases the chance of fibrosis and parenchymal damage.

The authors recommend the following indications for surgical interventions: (1) ipsilateral UPJ obstruction with less than 40% of differential renal function on diuretic renograms; (2) bilateral severe UPJ obstruction with renal parenchymal atrophy; (3) obstructive pattern on diuretic renograms with abdominal mass, urosepsis, or other symptoms (eg, cyclic flank pain, vomiting); and (4) recurrent UTI under antibiotic prophylaxis.

Patients with renal function better than 40% are monitored with repeat renal scans at 3- to 6-month and 12-month intervals, and surgery is performed only when a clear deterioration in renal function is present. In cases in which the differential function is less than 10%, some recommend the insertion of a nephrostomy tube to find out whether return of function will be sufficient; however, the disadvantages of nephrostomy are inevitable bacteriuria and the practical difficulty of maintaining a tube in an infant. Performing nephrectomy is rare in UPJ obstruction; however, if the differential function is less than 10%, nephrectomy can be considered to relieve recurrent infection or renal hypertension.

RELEVANT ANATOMY

Section 4 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

The UPJ is formed during the fifth week of embryogenesis, and, by weeks 10-12 of gestation, the initial tubular lumen of the ureteric bud becomes recanalized and the UPJ area is the last to recanalize.

Inadequate canalization of this area is the main embryological explanation of UPJ obstruction. Oestling folds, which resemble UPJ obstruction, are remnants of fetal renal development. No significant renal pelvic dilation or hydronephrosis are associated with this condition; however, most hydronephrotic kidneys now are detected prenatally.

UPJ obstruction is coexistent with other types of congenital abnormality in almost 50% of patients, and 10% of patients with UPJ obstruction show ipsilateral reflux. Voiding cystourethrogram is well warranted. In such cases, more severe anomalies should be treated first. Because of the nature of the blood supply of the ureter, simultaneous repair of both conditions is not recommended. Incidences of both the ureteropelvic and the ureterovesical junctions exist. In these cases, treat UPJ obstruction first because most distal ureteral obstruction is not severe. Duplication anomalies usually cause UPJ obstruction at the lower poles. In these cases, suspicion of vesicoureteral reflux also should be heightened.

CONTRAINDICATIONS

Section 5 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

The conditions that preclude the anesthesia are contraindications. Also, other common surgical contraindications (eg, coagulation abnormalities) should be ruled out before the definitive surgical treatment is performed.

WORKUP

Section 6 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Lab Studies

• Novel approaches may discern the clinically significant UPJ obstruction. These approaches are currently experimental.
• • Disruption of proximal tubular integrity leads to increased urinary concentrations of beta2-microglobulin (B2M), which normally is resorbed from the tubular lumen via phagocytosis and lysosomal digestion.
  • An increase in urinary concentrations of B2M may indicate tubular dysfunction as a result of the obstructive insult. Functionally significant obstruction and recovery from obstruction may be determined by following the urinary concentration of B2M.
  • The potential for B2M to be a marker for significant obstruction is quite appealing; however, the determination of its levels in obstructed kidneys is not routine, and many different insults other than UPJ obstruction can lead to increased levels of B2M in the urine. In addition, the immaturity of the nephron and the high fractional excretion of water in neonates contribute to elevated B2M levels in the absence of any identifiable renal stress.
  • Further observations of the concentration of this protein in urinary obstruction are necessary before its assessment can have practical application.
• N-acetyl-b-glucosaminidase (NAG) is a tubular lysosomal enzyme present in the urine of children who have various renal diseases. This is currently experimental.
• • In rats with experimental partial ureteral obstruction, the urinary concentration of NAG increases in the first 2 weeks of obstruction and decreases with the relief of obstruction.
  • In a clinical study, NAG levels in kidneys at the time of pyeloplasty were 7 times higher than those in bladder urine from normal control patients. In addition, enzyme levels in the bladder of patients 6 weeks after surgery suggested normalization of NAG excretion.
• Urinary biochemical markers of renal damage someday may aid the diagnosis of clinically significant urinary obstruction. These are currently experimental.
• • As described previously, many biologic modulators of glomerular dynamics and renal histology have been identified.
  • The assessment of urine for growth factors (eg, epidural growth factor [EGF], platelet-derived growth factor [PDGF], TGFb), cytokines, and vasoactive substances may be an important adjunct in evaluating obstructive uropathy in the future.

Imaging Studies

• Prenatal
• • Widespread use of antenatal ultrasonography has opened the new field of perinatal urology; however, even the most modern ultrasonographic techniques only demonstrate the dilation of renal pelvis and ureter and cannot accurately differentiate the true obstruction from a harmless physiologic dilatation.
  • During any session of prenatal ultrasonographic diagnosis, thoroughly investigate the following from the initial study usually performed between 16 and 20 weeks: amniotic fluid volume to rule out oligohydramnios, bladder volume, kidney size, anteroposterior diameter of the renal pelvis, and any associated abnormalities. Functionally significant hydronephrosis can be determined when the anteroposterior diameter of the renal pelvis is more than 10 mm, the ratio of the renal pelvis–to–anteroposterior renal cortex is more than 0.5, or evidence of caliectasis is present after 24 weeks of gestation. Following fetal hydronephrosis also is important to monitor possible progression. A recent meta-analysis of 7 studies of isolated antenatal hydronephrosis showed that 98% of patients with Society of Fetal Urology (SFU) grades 1-2 hydronephrosis (anterior-posterior pelvic diameter [APPD] <12 mm) resolved, stabilized, or improved during follow-up.
• Postnatal
• • After the prenatal presumptive diagnosis UPJ obstruction or other conditions causing hydronephrosis is made, the neonate should undergo ultrasonographic evaluation on the second or third day of life. Before this date, results may be false negative because of neonatal dehydration and physiologic oliguria; however, in cases of bilateral hydronephrosis, more rapid evaluation is warranted. Postnatal examination evaluation consists of urinary tract study whether the calyceal pelvic dilation with or without renal cortical thinning is present. Approximately 20% of antenatal hydronephrosis are not found on postnatal ultrasonogram.
  • At the same time, ultrasonographic evaluation on the contralateral kidney, bladder, and ureter is performed. VCUG also is done to rule out vesicoureteral reflux.
  • The renal scan and scintigraphy (ie, diuretic renogram) is the most widely used technique in the presence of hydronephrosis to assess function and obstruction. The rate at which tracer leaves the renal pelvis following diuretic injection, reflected in the slope of the drainage curve and often reported as T1/2 (the time required for 50% of the isotope to exit), is generally viewed as an accurate reflection of the patency of the UPJ. Rapid drainage (low T1/2) indicates no obstruction, while impaired drainage or slow or no washout (T1/2 >20 min) indicates obstruction.
  • The current radiopharmaceutical agent most widely used is technetium 99m diethylenetriamine pentaacetic acid (99mTc-DTPA). It is excreted by glomerular filtration and is not secreted or reabsorbed by the renal tubules. Another much more expensive agent is 99mTc-mercaptoacetyltriglyine (MAG3), which offers better anatomical resolution and can be used in case of decreased renal function. Variables include the use of intravenous hydration, the dosage and timing of administration of diuretic, the requirement for bladder catheterization, the degree of pelvic dilatation, the severity of outflow obstruction, and the method of calculating the clearance after the administration of diuretic.
  • The most useful measure in diuretic renography is the estimate of differential renal function. This is considered significant when it is less than 40%. This percentage usually is well correlated with the half-life (T1/2) washout curve. Therefore, as stated above, many factors must be considered when evaluating the renal scan, especially in neonates. For this reason, the T1/2 of the diuretic renogram cannot be a single indicator to determine surgery, especially in the neonate.
  • Supranormal differential renal function of the affected kidney in UPJO can occasionally be found on renal scans and has been hypothesized to be caused by an increase in single nephron filtration or nephron volume. However, in a study of histopathological changes of hydronephrotic kidneys with supranormal daily replacement factor (DRF) assessed with intraoperative kidney biopsy at the time of pyeloplasty, the glomerular area was not significantly larger than controls, but the probability for a larger renal glomeruli increased with decreasing DRF. Instead of increased nephron volume, the supranormal DRF can be accounted for by an increase in renal blood flow that results from tubuloglomerular feedback, prostaglandins, and the renin-angiotensin system as a protective mechanism from high intrapelvic pressure.
  • The degree of UPJ obstruction is information of utmost importance for patients, but no single test can demonstrate the degree of obstruction accurately and determine which patients require operative intervention. Imaging modalities can exhibit urinary tract dilation, but they offer no conclusive data whether to operate or observe. Radioisotope renogram and the pressure-perfusion test can reproduce significantly impaired washout of urine from the kidney; however, in many instances, kidneys have no measurable deterioration when observed for long periods. Nephrostomy drainage and assessment of creatinine clearance can indicate decreased differential renal function of the involved kidney, which does not necessarily change after surgery.
  • Lastly, the widespread use of modern imaging techniques has not led to an increase in the number of pyeloplasties that are performed. In a multi-institutional study that investigated the total number of pyeloplasties performed in a well-defined region, it was found that the total number of operations has remained constant since the late 1970s. The authors found that the number of pyeloplasties conducted in children aged 1-6 years increased, whereas the number of pyeloplasties in children aged 7-12 years decreased; yet, the total number performed per year stayed the same. In other words, the degree of hydronephrosis, impaired isotope washout, or even reduced differential renal function neither helps to define significant obstruction nor predicts deterioration.

Other Tests

• The development of Doppler sonography has become another useful diagnostic modality in the assessment of kidneys with UPJ obstructions. With duplex Doppler sonography, intrarenal vasculature can be assessed to determine the resistive index. Normal kidneys reliably demonstrate resistive indices less than 0.7, and obstructed kidneys show higher values. Administration of diuretics can aggravate the preexisting obstruction, thereby aiding the diagnosis by Doppler sonography. It is especially reliable in the preoperative diagnosis of aberrant-accessory blood vessels associated with UPJ obstruction.
• A functional study is then necessary to confirm the diagnosis of UPJ obstruction. The excretory urography (ie, IVP) has been used to evaluate UPJ obstruction, but IVP may not provide adequate information to determine the true obstruction, and it is especially difficult to interpret in children.
• IVP provides information about the obstruction and contralateral side and especially facilitates operative planning; however, infant urograms are compromised by the immature renal function, which impedes adequate visualization of the collecting system. Bowel gas and underlying bony structures also make interpretation of the urogram difficult. Despite such shortcomings, IVP accurately visualizes kidney, renal pelvis, ureter, and the exact point of obstruction. IVP also allows for clear visualizations of malrotated renal units.
• The drawbacks of IVP include the necessity of dehydration even in infants, which makes it a relatively risky procedure. Of course, a risk of radiation exposure exists, which can be minimized by limiting number of films taken. Problems associated with contrast media exist, such as nephrotoxicity and anaphylactic reactions. These problems can be reduced by the newer nonionic contrast agents that are currently available.
• CT scan has been used to diagnose UPJ obstruction in children, especially in association with the abdominal trauma. CT scans, like IVP studies, show the dilation of the kidney and collecting system well, and it may be used to estimate the differential renal function by measuring the cortical thickness. Spiral CT provides superior longitudinal resolution; vessels as small as 1 mm may be detected in the UPJ region. New developments in MRI technology have made it possible to image kidneys while assessing intracellular metabolic parameters independent of blood flow and tubular function. Relative high cost and the noise during the procedure limit the routine use of MRI for evaluating urinary obstruction in children.
• The retrograde pyelogram is one of the first tools that have been used to assess upper ureter and renal pelvis. After the advent of fiberoptic technology, routine endoscopic assessment became possible. The necessity of general anesthesia has made retrograde pyelography an adjunctive role, usually performed in the operating room to confirm the absence of coexisting lower ureteral obstruction.

Diagnostic Procedures

• The antegrade pressure-flow study was introduced by Whitaker and has proven useful in the equivocal obstruction in children. Koff and colleagues have characterized the volume-dependent changes in pressure and have classified patterns of pressure exit flow curves as simple or complex. The Whitaker measurement records the response of the renal pelvis to distention, which does not truly define obstruction. In the complex cases in which intrinsic and extrinsic obstruction coexist, this test does not provide conclusive evidence.

Histologic Findings

• This intrinsic obstruction is evident as the ureteral narrowing with angulation is found. During exploration, the catheter usually is passed to the renal pelvis without resistance, and this is evidence of the fact that the true narrowing is not a main pathologic change in UPJ obstruction. Some claimed the presence of remnant valve and others claimed the disproportionate abundance of longitudinal muscles as the cause of this condition. The most attractive theory is the obstruction secondary to muscular discontinuity. This absence or disorientation of smooth muscle fibers at UPJ is clearly evident on electron microscope evaluation with the findings of increased ground substance and collagen fibers; therefore, conduction of the peristatic wave is impeded.
• One study had identified altered expression of interstitial Cajal cells in obstructed UPJ specimens, which are normally intercalated between nerve terminal and smooth muscle cells, providing a means of transducing signals from neurotransmitters and mediating neurotransmission. This suggests that UPJO may cause the failure of transmission of peristaltic waves across the UPJ, resulting in the failure of urine to be propelled from the renal pelvis into the ureter.

TREATMENT

Section 7 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Medical therapy

The timing of surgical correction of hydronephrosis suggestive of UPJ obstruction in newborns is highly controversial. Those who support delayed management contend that for most newborns with relatively preserved differential renal function (>35% of differential renal function), hydronephrosis is a relatively benign disease without proof of progression. Renal function does not deteriorate; thus, immediate surgery is not necessary. In a study by Koff and associates, approximately 81 out of 104 patients were followed for 5 years; 7 (7%) of those patients ultimately required pyeloplasty, and, even in these cases, pyeloplasty successfully restored the differential renal function to predeterioration levels.

Researchers also observed that in 15 out of 16 patients with severe hydronephrosis (grade 4 hydronephrosis according to the Society for Fetal Urology Guidelines) associated with a differential renal function of less than 40%, spontaneous improvement occurred in the initial obstructive patterns on renal scans, and, for 6 of the patients, it became nonobstructed. Similar results were observed with ultrasonography that hydronephrosis disappeared in 6 kidneys and improved in another 6 kidneys.

Thus, the difficulty in determining the indication of surgical management is 2-fold. First, ultrasonography and diuretic renography to assess hydronephrosis are inaccurate and sometimes misleading. Second, some significant cases of hydronephrosis that are discovered by these modalities may not be obstructive at all. Therefore, Koff redefined obstruction as "any restriction to urinary outflow, which if untreated will injure the kidney" to provide a clinically useful guideline; Koff recommended that most unilateral hydronephrosis actually is nonobstructed and, thus, benign, which can be observed safely nonoperatively.

Surgical therapy

In the early 1980s, sonographic identification of obstruction in many infants resulted in a dramatic increase in the number of neonatal pyeloplasties performed. Initially, newborn pyeloplasty had a reported reoperation rate of 20%, which improved with the experience. The relative ease and safety of newborn pyeloplasty stimulated discussion about the necessity of intervention.

Physiologically, the newborn kidney is quite different than the adult kidney, particularly in the response to stimulation by the renin-angiotensin system. Renal function could be preserved by relieving the obstruction, achieving maximal benefit in the youngest of kidneys. Because renal failure caused by obstructive uropathy is a definite clinical dilemma, it may be appropriate to perform immediate pyeloplasty at the time of presentation, even in the asymptomatic infant.

Unilateral pyeloplasty not only improves hydronephrosis but also significantly increases creatinine clearance (as calculated by the Schwartz formula) and somatic growth. The implication is that unilateral obstruction has negative effects on renal function and on somatic growth.

The most compelling supporting data on early surgical correction come from animal experiments suggesting that prolonged partial ureteral obstruction is deleterious to the newborn kidney and can be reversed by early relief of the obstruction. Spontaneous resolution of hydronephrosis is not as benign as proposed by Koff and Campbell, that is 15-33% of patients with asymptomatic neonatal hydronephrosis show progressive ipsilateral renal deterioration, and about one half of them never regain the lost function by pyeloplasty.

There are 2 well-designed longitudinal studies that provide valuable information against initial observation and delayed management. According the study by Ransley and associates, of 100 infants with differential renal function of hydronephrotic kidney higher than 40% who were followed nonoperatively, 23 eventually underwent pyeloplasty during 6 years of follow-up care. Among these patients, 5 (36%) completely recovered renal function, 4 (29%) partially recovered, 3 (21%) had no change, and 1 (7%) further deteriorated after pyeloplasty. Thus, 8 of 100 initially well-functioning kidneys sustained permanent deterioration with this approach. Similar results were observed by Cartwright and Duckett, which included the results with 39 infants with a cut-off value of 35% of differential renal function. Six patients (15%) underwent pyeloplasty because of decreasing renal function, UTI, or pain.

The observation approach allows the physician to avoid risks associated with surgery and anesthesia, but there is a definite percentage of patients who sustain irreversible renal damage that could have been prevented by early pyeloplasty. Furthermore, after a short learning period, the pyeloplasty in infants is not demanding and is associated with little perioperative morbidity.

Preoperative details

When the diagnosis of a UPJ obstruction has been made, prompt intervention is appropriate to prevent or minimize renal damage. First, prophylactic antibiotic therapy is warranted in cases of moderate to severe dilatations because any UTI, especially in neonatal period, dramatically increases the chance of fibrosis and parenchymal damage.

Intraoperative details

Conventional techniques

The technique of complete ureteral transection followed by reanastomosis to the renal pelvis was first described in the management of a retrocaval ureter, but it was easily adapted for reconstructing the UPJ obstruction. Many different approaches have been tried, such as lumbotomy, flank, or anterior extraperitoneal incision, but the essence of repair consists of excision of the narrowed segment, spatulation, and anastomosis to the most dependent portion of the renal pelvis. Foley YV-plasty, a nondismembered type of repair, is useful in the repair of a kidney with high ureteral insertion and most cases of horseshoe kidneys; however, the Anderson-Hynes pyeloplasty, the most commonly used type of repair, has a high success rate with few complications in most cases.

Endourological techniques

Endourologic methods applied on UPJ obstruction include balloon dilatations, percutaneous antegrade endopyelotomy, and retrograde ureteroscopic endopyelotomy. In 1983, Wickham and Kellet established access to a hydronephrotic kidney and performed the first percutaneous pyelolysis. The concept was attractive and the technology was available. Soon, a large series of endopyelotomies in adults was reported with fairly good short- and long-term success rates of 70-85%. If an initial attempt of endopyelotomy fails, subsequent open pyeloplasty is still a viable option with a high success rate.

Laceration of the lower pole vessel, which is in anatomic relationship with the ureter in 40% of cases, must be avoided. Angiograms, endoluminal ultrasound, helical CT scans, and Doppler ultrasound have been used to identify the lower pole vessels. The best recommendation is to make sure that all incisions in the ureteral narrowing are directed laterally to minimize the chance for damage to the lower pole vessel.

Retrograde treatment of UPJ obstructions has been applied to children because of the technical advancements. This technique carries risk of significant stricture of the lower ureter. Balloon dilatations are most appropriate in pediatric populations because they are the least invasive approach and associated with the lowest risk of hemorrhage. However, the results generally do not match the open pyeloplasty, and most pediatric urologists continue to recommend open repair of primary UPJ obstruction.

This technique may be more useful in children older than 4 years with a failed pyeloplasty, where only a small dilation of the anastomosis may be required to produce good renal decompression. The technique involves a UPJ bridge with an endopyelotomy stent to drain the kidney and prevent the excessive scar formation that can occur with extensive urinary extravasation. The stent is removed after 6 weeks. Favorable factors include older age, secondary UPJ obstruction, low-grade hydronephrosis, and good renal function.

Laparoscopic techniques

Laparoscopic dismembered pyeloplasty, first introduced in 1993 by Schuessler, yields results that are comparable with those of open pyeloplasty, with success rates reported to be as high as 96-98% while still maintaining the benefits of endoscopic approaches, including less postoperative pain, short hospitalization, and reduced postoperative recovery time. However, the technical skills required for intracorporeal suturing and the lengthy operation time due to the degree of difficulty make it a costly procedure. Robot-assisted laparoscopic dismembered pyeloplasty is another recently introduced surgical treatment option.

Postoperative details

No specific guidelines exist for the stents and nephrostomy tubes in the postoperative period. In many instances, there is a chance of delayed opening of the anastomosis, thereby requiring the need for the nephrostomy tube. Another option is to stent the anastomosis with a double J catheter, but the stent is not commonly used in children because the procedure requires anesthesia. Many pediatric urologists tend to use neither stents nor nephrostomy tubes.

Follow-up

Postoperative evaluation is performed by a renal scan or excretory pyelography at 2-3 months. A further evaluation with ultrasound is recommended at 12-24 months, but, beyond that, late problems are uncommon in the absence of symptoms. A successful outcome does not always mean an improvement in the differential renal function as measured by renography. In most cases, the dismembered pyeloplasty improves the degree of hydronephrosis and washout on the renogram. The symptoms of pain, infection, and hematuria, if present before surgery, resolve along with the improvement of hydronephrosis.

For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education article Intravenous Pyelogram.

COMPLICATIONS

Section 8 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Postoperative obstruction is a difficult problem, and, faced with these circumstances, ureterocalicostomy may be performed as salvage procedure. The key features of the ureterocalicostomy technique consists of anastomosis of the ureter directly to the dependent portion of the lower pole calyx and trimming of the overlying renal parenchyma to prevent postoperative obstruction. This technique may require clamping of the renal artery. The difficulty of open reoperative surgery in patients with failed pyeloplasty makes the minimally invasive aspects of endopyelotomy seem attractive.

OUTCOME AND PROGNOSIS

Section 9 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

The overall success rate with the dismembered repair is quite satisfactory; most series report a success rate of higher than 90-95%. Long-term obstruction at the anastomosis can occur; but reoperation for this is low, occurring in 2-5% of cases.

Bleeding and infection are uncommon following pyeloplasty. Probably because of significant compliant capacity growing tissue, many cases of fetal hydronephrosis resolve before birth. Of those with hydronephrosis and preserved renal function at neonatal evaluation, 23% presented for delayed surgery in one series. On the other hand, some propose delaying surgical correction because newborn hydronephrosis is a relatively benign condition and a definite proportion of patients have spontaneous improvement.

The common early complications are prolonged urinary extravasation and delayed opening of the anastomosis. Urinary extravasation usually stops spontaneously, generally within 2 weeks. Delay in opening of the anastomosis is observed most often with the use of a nephrostomy tube without a stent across the anastomosis. Within 3 months of surgery, 80% of obstructed anastomosis eventually open.

Patients with lower percentages of elastin in the renal pelvis, UPJ proper, or ureter tended to show better resolution of hydronephrosis 6 months after pyeloplasty. Increased elastin of the renal pelvis and ureter might result in inelasticity and low compliance, which delays hydronephrosis improvement after pyeloplasty.

FUTURE AND CONTROVERSIES

Section 10 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Disruption of proximal tubular integrity leads to increased urinary concentrations of B2M, which normally is resorbed from the tubular lumen via phagocytosis and lysosomal digestion. An increase in urinary concentrations of B2M may indicate tubular dysfunction as a result of the obstructive insult. Functionally significant obstruction and recovery from obstruction may be determined by following the urinary concentration of B2M.

The potential for B2M to be a marker for significant obstruction is quite appealing; however, the determination of its levels in obstructed kidneys is not routine, and many different insults other than UPJ obstruction can lead to increased levels of B2M in the urine. In addition, the immaturity of the nephron and the high fractional excretion of water in neonates contribute to elevated B2M levels in the absence of any identifiable renal stress. Further observations of the concentration of this protein in urinary obstruction are necessary before its assessment can have practical application.

NAG is a tubular lysosomal enzyme present in the urine of children who have various renal diseases. In rats with experimental partial ureteral obstruction, the urinary concentration of NAG increases in the first 2 weeks of obstruction and decreases with the relief of obstruction. In a clinical study, NAG levels in kidneys at the time of pyeloplasty were 7 times higher than those in bladder urine from healthy control patients. In addition, enzyme levels in the bladder of patients 6 weeks after surgery suggested normalization of NAG excretion. Urinary biochemical markers of renal damage someday may aid the diagnosis of clinically significant urinary obstruction.

As described previously, many biologic modulators of glomerular dynamics and renal histology have been identified. The assessment of urine for growth factors (EGF, PDGF, TGFb), cytokines, and vasoactive substances may be an important adjunct in evaluating obstructive uropathy in the future.

Furthermore, detailed knowledge of the cytokine responses in the urothelium is necessary for a better understanding of the role of urothelial cellular reactions in congenital UPJO. This may provide the basis for early intervention to prevent exacerbation of congenital hydronephrosis in the future.

Lastly, the widespread use of modern imaging techniques has not led to an increase in the number of pyeloplasties that are performed. In a multi-institutional study that investigated the total number of pyeloplasties performed in a well-defined region, it was found that the total number of operations has remained constant since the late 1970s. The authors found that the number of pyeloplasties conducted in children aged 1-6 years increased, whereas the number of pyeloplasties in children aged 7-12 years decreased; yet, the total number performed per year remained the same. In other words, the degree of hydronephrosis, impaired isotope washout, or even reduced differential renal function neither helps to define significant obstruction nor predicts deterioration.

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

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