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Ureteral Obstruction and Malformations
Hydronephrosis and ureteral malformations are among the most common anomalies in the urinary tract in children. Many of these conditions are now detected prenatally. Urinary tract dilation is present in 1 in 100 fetuses, but significant uropathy is found in only 1 in 500 ( Fig. 54.1 ).
Normal kidneys are typically identifiable by 18 weeks in all fetuses. Dilated kidneys can be seen as early as 12–14 weeks of gestation. The arrow demonstrates left-sided caliectasis on a coronal fetal image.
Ureteropelvic Junction Obstruction in Children
With ureteropelvic junction (UPJ) obstruction, there is inadequate drainage of urine from the renal pelvis, resulting in hydrostatic distention of the pelvis and intrarenal calyces. The combination of increased intrapelvic pressure and urine stasis in the collecting ducts results in progressive damage to the kidney.
Historically, the incidence of UPJ obstruction has been estimated at 1 in 5000 live births. However, with the advent of antenatal ultrasonography (US), the prevalence of dilation has been found to be much higher. Retrospective reviews show that although the incidence of detected dilation has increased, the actual number of operations for UPJ obstruction has been relatively constant at 1 in 1250 births. UPJ obstruction is more common in boys (2:1), and two-thirds occur on the left side. Bilateral dilation occurs in 5–10% of patients and is much more frequently seen in younger children. Bilateral obstruction is much less common.
Etiology
During development of the upper ureter, the lumen of the ureteral bud solidifies, which is followed by ureteral lengthening and later recanalization. Failure to recanalize completely is thought to be the cause of most intrinsic UPJ obstructions. Other causes of intrinsic UPJ obstruction include ureteral valves, polyps, and leiomyomas.
The most common finding is ureteral narrowing of a variable length that joins the renal pelvis above the expected dependent position. At low volume, peristaltic waves of urine cross the UPJ. However, as the flow increases beyond a certain threshold, the renal pelvis dilates. The dilated pelvis may kink the ureter further, increasing the pressure in the pelvis. In 20–30% of patients, the ureter is draped over a lower-pole vessel, producing an extrinsic UPJ obstruction. In most of these patients, there is also a coexisting intrinsic narrowing of the ureter.
Histologic evaluation reveals a decrease or complete absence of smooth muscle fibers at the UPJ. Electron microscopy may show an increase in collagen deposition between the muscle fibers that is most likely a response to the obstruction as opposed to the cause. Fibrosis and interruption of the smooth muscle continuity block transmission of the peristaltic wave, while defective innervation also may play a role. UPJ obstruction also can be secondary (i.e., related to other ureteral pathology). It can be found in conjunction with high-grade vesicoureteral reflux (VUR), after cutaneous ureterostomy, and after decompression of the dilated urinary tract. VUR has been found in 15% of patients with UPJ obstruction ( Fig. 54.2 ).
Clinical Presentation
Most renal dilation and obstruction are detected prenatally. Less frequently, it is detected because of an abdominal mass, urinary tract infection (UTI), or associated with other congenital anomalies (i.e., VACTERL [vertebral, anal, cardiac, tracheoesophageal fistula, renal, limb] syndrome). In older children, vague, poorly localized, cyclic or acute abdominal pain associated with nausea is common ( Fig. 54.3 ). Some of these children are initially seen by gastroenterologists for their symptoms. The cause of the intermittent obstruction is unclear, but renal function is almost always preserved. Hematuria after minor trauma or vigorous exercise can be a presenting feature, most likely secondary to rupture of mucosal vessels in the dilated collecting system.
Diagnosis
When the antenatal diagnosis of UPJ obstruction is made, the initial postpartum evaluation should be performed at 10–14 days of life to avoid false-negative studies resulting from the transitional nephrology of the newborn. Bilateral renal pelvis dilation is rarely associated with significant enough obstruction to cause oligohydramnios and warrant antenatal intervention. US confirms the presence of pelvic and calyceal dilation, with variable thinning of the renal parenchyma. US is useful for evaluating the contralateral kidney, the bladder, and the distal ipsilateral ureter to avoid confusion with a ureterovesical junction (UVJ) obstruction, but it does not provide functional information. The Society for Fetal Urology (SFU) classification has typically been used to describe the degree of dilation ( Fig. 54.4 ). A newer urinary tract dilation (UTD) classification system is gaining favor across specialties including obstetrics, radiology, and urology as a way to standardize terminology for pre- and postnatal imaging ( Table 54.1 ). The presence of corticomedullary junctions is indicative of preserved function. In the past, routine antibiotic prophylaxis was given to all infants with prenatal pelvic dilation, but the risk of a UTI is very small in the absence of reflux. A voiding cystourethrogram (VCUG) was also previously recommended in all patients being evaluated for UPJ obstruction, as VUR increases the chance that infection will occur, even in a partially obstructed system. Between 5% and 30% of infants with prenatally detected dilation will have reflux, and the majority will spontaneously resolve without an infection. Children with isolated pyelectasis and no ureteral dilation have a very low incidence of reflux, and the clinical yield from a screening VCUG is low.
Table 54.1
Postnatal Classification Criteria for Urinary Tract Dilation (UTD)
| UTD P1: Low Risk |
UTD P2: Intermediate Risk |
UTD P3: High Risk |
|
|---|---|---|---|
| Calyceal dilation | Central | Peripheral | Peripheral |
| Renal pelvis diameter (mm) | 10–15 | >15 | >15 |
| Parenchymal thickness | Normal | Normal | Abnormal |
| Parenchymal appearance | Normal | Normal | Abnormal |
| Ureters | Normal | Abnormal | Abnormal |
| Bladder | Normal | Normal | Abnormal |
P, postnatal. The highest grading parameter identified defines the overall UTD score. In other words, an otherwise normal kidney with ureteral dilation would be UDT P2.
The diuretic isotopic renogram is very useful for evaluating hydronephrosis, differential renal function, and renal drainage ( Fig. 54.5 ). In this study, the transit of an injected radioisotope through the urinary tract is monitored by a gamma camera. The early uptake (first 1–2 minutes) of the tracer indicates the split renal function, while the washout, augmented by the administration of a diuretic, is plotted by a computer to evaluate drainage. The study is obtained with either 99m Tc-mercaptoacetyltriglycine ( 99m Tc-MAG3), whose clearance is predominantly via proximal tubular secretion, or with technetium-99m-labeled diethylenetriamine pentaacetic acid ( 99m Tc-DTPA), whose renal clearance is by glomerular filtration. 99m Tc-MAG3 is more efficiently excreted than 99m Tc-DTPA and gives better images, particularly in patients with impaired renal function.
The technique for diuretic renography is standardized. Patients should be hydrated intravenously (15 mL/kg) 15 minutes before injection of the radionuclide. An indwelling catheter maintains an empty bladder and monitors urine output. The diuretic (1 mg/kg furosemide, up to 40 mg) is not administered until the activity peaks in the hydronephrotic kidney and renal pelvis. The tracer activity is then monitored for an additional 30 minutes, and a quantitative analysis is performed. Historically, persistence of >50% of the tracer in the renal pelvis 20 minutes after diuretic administration (
) is diagnostic of obstruction, although the applicability of this threshold in pediatric patients is debatable. False-positive results may occur when the immature neonatal kidney fails to respond to diuretic, when the diuretic is administered prior to maximal renal pelvic distension, when the patient is dehydrated, when the bladder is distended, or when the renal pelvis is significantly dilated.
Magnetic resonance urography (MRU) can be used at any age. T2-weighted images are independent of renal function, and hydronephrosis is readily detected. The anatomic images are excellent ( Fig. 54.6 ). Enhanced MR images with gadolinium can give information regarding differential function if one kidney is anatomically and functionally normal, and combines detailed anatomic and functional data with a single study. These potential advantages of MR imaging must be weighed against its high cost, need for sedation or general anesthesia, and long study times. These drawbacks limit its use for isolated unilateral renal dilations, but it may be valuable in cases with unusual or complex anatomy.
Rarely, when imaging is equivocal, invasive pressure flow studies may be indicated. These tests assume that obstruction produces a constant restriction to outflow that necessitates elevated pressure to transport urine at high flow rates. However, not all obstructions are constant. If the obstruction is intrinsic, a linear relationship exists between pressure and flow. However, in some cases, the results may reflect only the response of the renal pelvis to distention and may be positive in the absence of obstruction. These studies require general anesthesia in children and have limited applicability.
Retrograde urography at the time of operative correction is helpful if uncertainty exists regarding the site of obstruction. This is rarely required because a well-performed US evaluation and radionuclide study will exclude distal obstruction. As there are risks with using instruments in the infant male urethra and the ureteral orifice, these retrograde studies are not routinely performed.
Management
Indications for Intervention
Intermittent obstruction and pain are probably the most reliable indication for operation. Diminished function, delayed drainage, progression of pelvic and calyceal dilation on US, and loss of renal function are all potential indicators of obstruction. Randomization to operative and observational arms is complicated by a difficult decision that a parent has to make for the asymptomatic child. The morphologic appearance of a dilated renal pelvis on excretory urography or US is not a good indication for operation because many of these findings will resolve without an operation (see Fig. 54.5 ). Neonatal hydronephrosis can often be explained by physiologic polyuria and natural kinks and folds in the ureter.
The ongoing debate in the management of neonatal UPJ obstruction centers on the definition of significant obstruction. Some authors have tried to set objective criteria for predicting the need for operative intervention such as renal pelvis diameter, renal parenchymal measurements, or differential renal function, but the inherent limitations in renography still leave questions in these studies as to whether every child that progressed to operation absolutely needed it. Diuretic renography has limitations in the neonate, although using the “well-tempered” approach increases its value. The standard half-time of 20 minutes for obstruction in the neonate is misleading in many cases. Differential renal function or individual kidney uptake is the most useful information obtained during renography. An indication for operation is diminished renal function in the presence of an obstructive pattern on renography. Although the threshold is arbitrary, most pediatric urologists believe that <35–40% function in the hydronephrotic kidney warrants correction. However, in one study looking at patients with dilated kidneys and no more than 25% total renal function, they were found to improve to >40% of total function in all cases without operative correction. Long-term studies of kidneys with >40% function have shown that fewer than 15–20% will require operation for diminishing function, UTIs, or unexplained abdominal pain. Some of these kidneys will regain some of the lost function.
The concern with an observational approach is that delaying correction until there is measurable deterioration in the renal function is not optimal. In the past, urinary stasis (infection, calculi, hypertension, and pain) was the indication for operative correction. Whether more emphasis should be placed on stasis and less emphasis on differential renal function is an unanswered question. Pyeloplasty can be safely performed in the infant. Early intervention eliminates the indefinite period of surveillance. The decision to follow neonates nonoperatively requires vigilance and parental cooperation to avoid complications. There has been increasing interest in recent years in utilizing serum or, ideally, noninvasive urine biomarkers as an adjunct to imaging to determine the need for surgical correction. Potential candidate markers include transforming growth factor (TGF)-β1, monocyte chemotactic protein (MCP)-1, endothelin-1, and carbohydrate antigen (CA) 19-9, but these efforts are still in the investigational phase and are not widely used in clinical practice.
If the child is initially seen with acute pain or infection, it is advisable to wait 1–2 weeks to allow the inflammation to resolve. Percutaneous drainage or stent placement for sepsis is rarely required preoperatively. It should be avoided in the absence of infection because of the inflammation that develops from a tube in the renal pelvis. Exploration for a poorly functioning kidney requires an assessment of the renal parenchyma. If the parenchyma is grossly dysplastic or frozen-section analysis shows dysplasia, then nephrectomy should be performed. Unfortunately, no test accurately predicts recovery of function. Thus, nephrectomy is rarely performed in the infant with UPJ obstruction.
Operative Techniques
A dismembered pyeloplasty is the preferred technique to correct UPJ obstruction ( Fig. 54.7 ). A successful outcome is achieved with construction of a funnel-shaped, dependent UPJ complex. The renal pelvis and upper ureter are mobilized, and the ureter is divided just below the obstructed segment. It is spatulated on its lateral border through the aperistaltic segment. It is sometimes necessary to resect some of the renal pelvis to avoid postoperative obstruction. If this segment is particularly long, a flap of renal pelvis can be created. The Foley YV-plasty and the Culp spiral flap techniques were designed to maintain the continuity of the ureter and the pelvis. These techniques are used in unusual cases of malrotation, fusion anomalies, or long, stenotic segments.
The anastomosis is usually performed with 6-0 polydioxanone or 6-0 polyglycolic acid. The anastomosis begins at the most dependent portion of the pyeloplasty with placement of interrupted everting sutures that do not bunch the tissues and cause obstruction. After the anastomosis to the dependent portion of the pelvis is completed, the remainder of the ureter and pelvis can be approximated with continuous suture, taking care to irrigate any clots from the pelvis before the closure is completed. It is not necessary to pass a catheter distally into the bladder because preoperative studies should have excluded a distal obstruction.
Pyeloplasties are frequently performed without diversion, so it is important to be as gentle as possible. Excessive handling of the pelvis and ureter increases edema. A stent is typically left after a laparoscopic repair. Even if an anastomotic leak occurs, a satisfactory outcome usually results. A Penrose drain may be left near the anastomosis and can usually be removed within 48 hours. If drainage is prolonged, the child can be discharged with the drain in place. Renal drainage is definitely indicated in solitary kidneys or when simultaneous bilateral pyeloplasties are performed. In a reoperation, it is technically more difficult to achieve a watertight anastomosis and internal drainage (stent, nephrostomy or nephrostent) is indicated.
Extrinsic UPJ obstruction associated with an aberrant lower-pole vessel requires division of the ureter at the UPJ and performance of a standard dismembered pyeloplasty after transposing the ureter to a nonobstructed position. This technique is the standard laparoscopic approach and is preferable to transposition of the crossing vessel. In the case of an intrarenal pelvis or when significant scarring is found at reoperation, a ureterocalicostomy is a useful technique. A portion of the lower pole should be resected to prevent a postoperative stricture. The ureter is spatulated and then anastomosed to the exposed calyx in the lower pole.
Laparoscopic pyeloplasty has been performed in all ages, and the age of the patient is inversely related to benefits of decreased pain and convalescence. However, the open approach still has a role in infants and young children. Open pyeloplasty can be performed through a flank, anterior extraperitoneal approach, or posterior lumbotomy approach. The anterior approach involves a transverse incision from the edge of the rectus to the tip of the 12th rib. The retroperitoneum is entered and the UPJ is exposed, with the kidney left in situ. In infants, this is a muscle-splitting incision with low morbidity. The dorsal lumbotomy approach also can be easily performed in infancy and provides direct access to the UPJ. The kidney does not require mobilization, and the ureter and renal pelvis can usually be delivered out of the incision. In bilateral cases, the child does not need to be repositioned. The lumbotomy approach should not be used with a malrotated kidney or a kidney that has an intrarenal pelvis. For a second operation, when an open approach is used, the anterior or flank approach is typically preferred over the dorsal lumbotomy technique. However, laparoscopy and endopyelotomy have seen increasing use in reoperative pyeloplasty.
Endoscopic approaches (endopyelotomy) for UPJ obstruction were popularized in the 1980s and 1990s but have been replaced by laparoscopic approaches. Endopyelotomy successfully relieves primary UPJ obstruction in 70% of children. As this success pales in comparison to pyeloplasty, it is not routinely utilized for primary repair. Endopyelotomy clearly has a role in recurrent UPJ obstruction, in which the success rate is >95%. Depending on the age of the patient and the size of the ureter, this can be performed in either an antegrade or retrograde fashion ( Fig. 54.8 ).
The first laparoscopic pyeloplasty in a child was reported in 1995 by Peters et al., and the first series was published by Tan in 1999. Laparoscopic pyeloplasty has been reported in children as young as 2 months. The introduction of robotic surgery with articulating instruments and three-dimensional visualization has made intracorporeal suturing easier and more precise. The success rates of open, laparoscopic, and robotic pyeloplasties are equivalent. Robotic instrumentation adds cost but may decrease the hospitalization or minor postoperative complications according to some authors. The benefits of laparoscopic and robotic surgery over an open approach may include a decreased length of hospitalization, decreased analgesic requirements, improved cosmesis, and quicker return to normal activity, which likely have increasing benefit with increasing age of the patient.
Laparoscopic pyeloplasties are mostly performed using the Anderson–Hynes dismembered technique ( Fig. 54.9 ). This can be performed through either a transperitoneal or retroperitoneal approach using a similar technique once access and exposure are obtained. With both transabdominal and retroperitoneal approaches, the child is placed on the operating table in a flank or modified flank position.
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