Ureteral Obstruction and Malformations Flashcards
Discuss obstructive uropathy.
Obstructive uropathy is the leading cause of chronic kidney disease in children. It may be caused by upper or lower urinary tract obstruction and most often hydronephrosis on renal ultrasound is the first indicator of obstruction. The key in management of these patients is determining if hydronephrosis is due to obstruction, and this can be done with further imaging such as a nuclear scan or magnetic resonance urography. Once obstruction is confirmed, the crucial step is to bypass the level of obstruction and drain the urinary tract so as not to compro- mise renal function.
What is the leading cause of chronic kidney disease in children?
Congenital urinary tract obstruction is the #1 cause of chronic kidney disease in males under 1 year old, and is one of the most common diagnosis in children undergoing renal transplant for end stage renal disease [1].
What are common causes of pediatric obstructive uropathy?
a. Ureteropelvic junction obstruction
b. Ureterovesical junction obstruction
c. Ureterocele
d. Ectopic ureter
e. Posterior urethral valves.
How is obstruction diagnosed?
Hydronephrosis on renal ultrasound (RUS) is usually the first indication of under- lying urinary tract obstruction.
The Society for Fetal Urology (SFU) developed a grading system for reporting hydronephrosis on RUS [2]. The higher the grade, the worse the hydronephrosis.
Grade 0: No splitting of renal pelvis
Grade 1: Splitting
Grade 2: Dilated renal pelvis and major calyces
Grade 3: Dilated renal pelvis, major and minor calyces
Grade 4: Dilated renal pelvis, major and minor calyces, thinned renal parenchyma
The Urinary Tract Dilation (UTD) classification system risk stratifies based on prenatal and postnatal RUS characteristics and anterior-posterior renal pelvis diameter (AP RPD) [3].
PRENATAL UTD CLASSIFICATION 1) UTD A1 (low risk) - AP RPD (mm): 16–27 wk: 4 to ≤7 ≥28 wk: 7 to ≤10 - Central or no calyceal dilation
2) UTD A2-3 (increased risk)
- AP RPD (mm):
16–27 wk: ≥7
≥28 wk: ≥10
- Peripheral calyceal dilation
- Parenchymal thickness abnl
- Parenchyma appearance abnl - Ureters abnormal
- Bladder abnormal
- Unexplained oligohydramnios
POSTNATAL UTD CLASSIFICATION 1) UTD P1 (low risk) - AP RPD (mm) 10 to <15 - Central calyceal dilation
2) UTD P2 (intermediate risk)
- AP RPD (mm): ≥15
- Peripheral calyceal dilation
- Ureters abnormal
3) UTD P3 (high risk)
- AP RPD (mm): ≥15
- Peripheral calyceal dilation
- Parenchymal thickness abnl
- Parenchyma appearance abnl - Ureters abnormal
- Bladder abnormal
How do you determine if hydronephrosis is due to obstruction?
Renal function and drainage must be assessed. This can be done with a MAG3 diuretic renal scan or with magnetic resonance urography (MRU).
The MAG3 scan requires an IV and a urinary catheter if not toilet trained.
The radiotracer is injected intravenously and within the first 2–3 minutes radiotracer uptake by the renal parenchyma is detected (radiotracer binds to the proximal tubules).
The differential renal function is determined at this point. Normal differ- ential renal function should be 50/50, with an accepted error of ±5%. At approximately 20 minutes, furosemide is administered intravenously and the drainage curves are analyzed.
The time is takes for half of the radiotracer to clear the renal pelvis is called the “t 1/2”.
An obstructed kidney will have a flat, or plateaued, drainage curve, and a t 1/2>20minutes.
An unobstructed kidney will have a down-slopping drainage curve and a t1/2 < 15 minutes.
Magnetic resonance urography (MRU) is a newer imaging modality that utilizes gadolinium-dTPA.
The advantage of MRU is that in addition to determining function and drainage, it also provides excellent anatomical evaluation.
The disadvantages of MRU are the need for sedation, cost, and limited availability.
What is the Whitaker test [4]?
The Whitaker test measures the pressure needed to propel fluid through the upper urinary tract at a fixed rate.
Under anesthesia, a nephrostomy tube is inserted into the renal pelvis and the collecting system is perfused at a continuous rate while simultaneously measuring the pressure in the renal pelvis.
In an obstructed system, renal pelvis pressures measure>20 cmH2O.
The invasiveness of this procedure has resulted in its limited use, however it can be helpful in equivocal cases.
Additionally, if performed in the fluoroscopy suite, simultaneous antegrade imaging studies can be obtained to help further assess the anatomy.
When should a voiding cystourethrogram (VCUG) be obtained in a patient with hydronephrosis?
According to the American Urological Association guidelines, a VCUG is rec- ommended in children with SFU grade 3 or 4 hydronephrosis [5].
This recommendation is based not only on the risk of vesicoureteral reflux (VUR), but also the potential for bladder outlet obstruction.
One should have a high index of suspicion for posterior urethral valves (PUV) if a male infant has a thickened trabeculated bladder with bilateral hydroureteronephrosis.
VCUG is the gold standard for diagnosing PUV, and imaging will show a dilated posterior urethra that funnels abruptly at the valves and a trabeculated bladder with a hypertrophied bladder neck.
Approximately 50% of patients with PUV will also have high grade VUR.
Patients with prenatally diagnosed hydronephrosis without PUV have an incidence of vesicoureteral reflux (VUR) of 16%.
VUR coexists with UPJ obstruction in approximately 10% of children.
What is the incidence of prenatal hydronephrosis?
Due to the increased use of ultrasound screening in the second trimester, the incidence of prenatal hydronephrosis is 1:100 to 1:500 [2].
What are antenatal signs of obstructive uropathy?
Prenatal ultrasound may show hydronephrosis, a distended bladder, and dilated posterior urethra (“keyhole” sign).
After 16 weeks gestation, amniotic fluid is mostly comprised of fetal urine, therefore fetuses with obstructive uropathy may have oligohydramnios.
Since amniotic fluid is vital to pulmonary development, oligohydramnios can result in pulmonary hypoplasia and there may be significant respiratory distress at birth.
Oligohydramnios can also result in Potter facies, club- feet and deformed hands, and poor abdominal muscle tone.
What is the timeline for postnatal imaging in a patient with prenatal hydronephrosis?
RUS should be obtained after 48 h of life. If the RUS is performed too early, it may underestimate hydronephrosis due to the relative oliguria shortly after birth.
If prenatal imaging in boys shows bilateral hydroureteronephrosis and/or thick- ened bladder with “keyhole” sign, a VCUG should be performed as soon as possi- ble to evaluate for PUV.
For patients with hydronephrosis that do not have PUV, a follow up RUS can be performed in 3–6 months to reassess the degree of hydronephrosis.
If hydronephrosis is persistent or worsening, a MAG-3 and/or VCUG can be ordered at this time.
Imaging can be ordered sooner if there is a clinical change, such as a febrile urinary tract infection.
What is the initial management for a patient with PUV?
First, a catheter (small feeding tube or coude catheter) should be placed to drain the bladder.
The balloon should not be inflated as this can obstruct the ureteral orifices in these small hypertrophied bladders.
Once the child is stable, they can be taken to the operating room for cystoscopy and valve ablation.
Ablation can be performed with a cold knife, bugbee, or laser.
A catheter is left in place for 24 hours after the procedure and a VCUG is performed one month after ablation to confirm success.
An alternative to valve ablation is creation of a vesicostomy.
This allows for decompression of the upper tracts and bladder, and valve ablation can be performed when the child is bigger.
Children with PUV have a 50–60% risk of UTI, therefore circumcision is recommended to reduce this risk.
What are the clinical outcomes of PUV?
Patients with PUV have renal dysplasia and require long term monitoring of renal function.
Studies have shown that the serum nadir creatinine level in the first year of life correlates with the need for renal replacement therapy (RRT), with 100% of patients with Cr > 1 requiring RRT by 10 years old [6].
Patients with PUV also have significant polyuria that worsens bladder dysfunction, and 26% of patients will require intermittent catheterization [6].
What causes UPJ obstruction?
In infants, the most common cause of UPJ obstruction is an intrinsic narrowing of the UPJ. In older children and adolescents, the most common cause is extrinsic compression from a crossing lower pole vessel.
What is the management of UPJ obstruction?
Dismembered pyeloplasty is the gold standard for the treatment of UPJ obstruction.
This can be performed open, laparoscopically, or robotically.
If a patient initially presents with uncontrollable pain or acute infection, a nephrostomy tube can be placed to decompress the collecting system until definitive surgery.
What are the principles of management for an ectopic ureter or ureterocele?
Ectopic ureters and ureteroceles are commonly associated with the upper pole of a duplex collecting system, which is evident on RUS as upper pole hydronephrosis.
The goals of management are to preserve renal function, prevent infection or reflux, and maintain urinary continence.
If there is adequate upper pole function, ureteroureterostomy or common sheath ureteral reimplant can be performed.
If there is no upper pole function, upper pole heminephrectomy is an option.
How does management of ureterocele differ from ectopic ureter?
Ureteroceles can be large and result in obstruction of the lower pole or contralateral ureter.
They can also prolapse and cause bladder outlet obstruction.
If the ureterocele is causing obstruction or if the patient is acutely ill from infection, they should be punctured endoscopically.
What is the incidence of 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.
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What causes ureteropelvic junction obstruction in children?
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.
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How is UPV junction obstruction diagnosed?
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.
The diuretic isotopic renogram is very useful for evaluating hydronephrosis, differential renal function, and renal drainage. 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 ( t 1 / 2 > 20 ) 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. 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.
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What are the surgical approaches to UPJ obstruction?
A dismembered pyeloplasty is the preferred technique to correct UPJ obstruction.
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 musclesplitting 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.
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. 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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What is the most common ureteral anomaly?
Duplication is the most common ureteral anomaly.
Both sides are equally affected, and girls are affected twice as often as boys.
The autopsy incidence is approximately 1%, but the incidence was 2–4% in older clinical series in which pyelograms were obtained for urinary symptoms.
Many of the duplicated units show congenital dysplasia (scarring) and hydronephrosis.
There is an increased incidence of infection because both VUR and obstruction are much more common in duplicated systems.
A partial or complete duplication of the ureter occurs when a single bud branches prematurely or when two ureteral buds arise from the mesonephric duct respectively. A bifid renal pelvis is the highest level of bifurcation and occurs in 10% of the population.
Other incomplete duplications occur throughout the ureter. An inverted-Y ureter is the rarest of all branching anomalies. This is presumably the result of separate ureteral buds that fuse before entering the metanephros.
In complete duplications, reflux into the lower renal moiety is the most common cause of renal disease. The more caudal ureteral bud ends up being located laterally and cranially in the bladder, and has a shorter intramural tunnel. The upperpole ureter enters the bladder adjacent to or distal to the lower ureter, as defined by the Weigert–Meyer law.
Reflux is identified in up to two-thirds of children with duplicated systems that develop infection. Reflux may occur into the upper-pole ureter if the ureteral orifices are immediately adjacent, or if the upper ureter is located distally at the level of the bladder neck without any submucosal support.
The treatment of VUR in duplicated ureters follows the same principles as that in a single system. Initial treatment includes preventive antibiotics and radiographic monitoring.
Low grades of VUR are associated with the same rate of spontaneous resolution as a single system.
The distal ureters share a common vascular supply, so reimplantation involves mobilization and reimplantation of the common sheath.
If an associated lower-pole UPJ obstruction is noted, ipsilateral end-to-side pyeloureterostomy is an effective management for both obstruction and reflux.
Even if significant scarring is present in the lower pole, reimplantation is usually effective unless major ureteral dilation is present.
In the latter case, lower-pole nephroureterectomy may be needed.
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What is a retrocaval ureter?
The retrocaval or circumcaval ureter is a right ureter that passes behind the inferior vena cava (IVC).
This results from a developmental error in the formation of the IVC.
The supracardinal vein (IVC) lies dorsal to the developing ureter, whereas subcardinal veins lie ventral to the ureter.
If the subcardinal vein persists as the IVC, the ureter passes behind the IVC and anterior to the iliac vein.
If both veins persist, the ureter passes between the duplicated IVC.
Symptoms are related to chronic ureteral obstruction and infection, and rarely occur in children.
The radiographic appearance depends on the level of obstruction. The more common distal obstruction appears as a “reversed J” on intravenous pyelogram.
Less commonly, the ureter crosses at the level of the UPJ. Both of these can be confused with UPJ obstruction and should be suspected when pyelectasis and dilation of the upper third of the ureter are seen.
Treatment is required only when significant obstruction or symptoms are present. Reconstruction is essentially a dismembered ureteroplasty with division of the ureter and anastomosis anterior to the IVC.
The other option is division and reconstruction of the IVC, which is more problematic.
Laparoscopic repairs have been successful with and without robotic assistance.
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What is a megaureter?
Megaureter is not a diagnosis but a descriptive term for a dilated ureter.
Normal ureteral diameter in children is rarely >5 mm.
Ureters >7 mm are considered megaureters.
The US appearance of the dilated and tortuous ureter is usually striking. Pelvicalyceal dilation and parenchymal scarring or thinning depend on the primary disease process.
Megaureter is the second most common urinary tract abnormality detected prenatally. Infection and intermittent abdominal pain can be presenting symptoms.
Primary obstructive megaureter is most commonly caused by a distal adynamic ureteral segment, but ureteral valves and an ectopic ureteral insertion can also cause obstruction.
Proximal smooth muscle hypertrophy and hyperplasia are seen.
A normal caliber catheter will usually pass through the distal 3–4 mm segment, but the peristaltic wave does not propel urine across this area. This absent peristalsis is not a result of a ganglionic abnormality as seen in megacolon.
The distal ureter may exhibit a variety of histologic abnormalities, but the common finding is a disruption of muscular continuity in the ureter that prevents propulsion of urine.
These anomalies can be classified as nonobstructed, refluxing, or obstructed. Some ureters also have reflux and simultaneous obstruction.
Standard imaging allows classification and appropriate management.
The diagnosis of a nonobstructed, nonrefluxing megaureter is one of exclusion, and is made only when the secondary causes of megaureter have been excluded and diagnostic tests do not show obstruction.
Box 54.1 gives clinical examples of each classification.
Any normal ureter will dilate if the volume of urine exceeds emptying capacity. Moreover, bacterial endotoxins and infection alone can cause dilation that will resolve after treatment of the infection.
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US almost always distinguishes megaureters from UPJ obstruction. The degree of distal ureteral dilation is often much more pronounced than the degree of renal pelvic dilation or caliectasis. A VCUG should be obtained in all patients. If significant reflux is found, delayed drainage films should be obtained to exclude simultaneous obstruction with a normal caliber distal ureteral segment. In a partially obstructed system, the contrast density in the ureter is decreased because of dilution related to stasis in the ureter (see Fig. 54.13).
Diuretic renography is useful for assessing function and drainage. The markedly dilated ureter can be a significant source of stasis, and determination of the drainage half-time can be difficult. Diuretic administration must be delayed because the system is so capacious and can take 60–90 minutes to fill. MRU is gaining increasing popularity, particularly in patients with complex anatomy, due to its ability to provide both anatomic and functional information. However, this information must be weighed against the increased cost and need for sedation or general anesthesia in some children.
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What is an ectopic ureter?
An ectopic ureter is defined as one that does not drain on the trigone, but enters at the bladder neck or more caudally.
Embryologically, this results from a cranial insertion of the ureteral bud on the mesonephric duct that allows distal migration with the mesonephric duct as it is absorbed into the urogenital sinus.
The incidence of ureteral ectopia is approximately 1 in 2000. Eighty percent of ectopic ureters are reported in association with a duplicated renal system.
As clinical problems are more common in girls with ectopia, only 15% of ectopic ureters have been reported in boys.
Ectopia is bilateral in 20% of patients.
Single ectopic ureters are rare but are more common in boys.
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How are ureterocoeles diagnosed?
Most ureteroceles are identified prenatally although 10–15% still present postnatally due to infection.
The obstructed renal unit may be palpable, but most have no clinically apparent abnormality. Bladder outlet obstruction is rare because most ureteroceles decompress during micturition, but the most common cause of urethral obstruction in girls is prolapse of a ureterocele (Fig. 54.16).
Abdominal US reveals a well-defined cystic intravesical mass that is located within the posterior bladder wall. This can be followed to a dilated ureter in the pelvis and to upper-pole hydroureteronephrosis in a duplicated system. The thickness and echogenicity of the renal parenchyma are often consistent with dysplasia and poor function.
A VCUG typically shows ipsilateral lower pole or contralateral reflux.
During cystoscopy, the bladder should be examined when it is full and also completely empty because compressible ureteroceles may not be evident in a full bladder or may appear as a bladder diverticulum. The dilated lower end of an ectopic ureter or megaureter may elevate the trigone, creating the cystoscopic, radiographic, and US appearance of a ureterocele, a so-called pseudoureterocele.
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