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Urology > Hydronephrosis and Ureter Disorders
Megaureter and Other Congenital Ureteral Anomalies
Article Last Updated: Feb 9, 2007
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Eugene Minevich, MD, Assistant Professor, Department of Surgery, Division of Pediatric Urology, University of Cincinnati
Eugene Minevich is a member of the following medical societies: American Academy of Pediatrics, American College of Surgeons, and American Urological Association
Coauthor(s):
Leslie Tackett, MD, Fellow, Departments of Surgery and Pediatrics, Division of Pediatric Urology, Children's Hospital Medical Center at Cincinnati
Editors: Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Mark Jeffrey Noble, MD, Consulting Staff, Urologic Institute, Cleveland Clinic Foundation; J Stuart Wolf, Jr, MD, FACS, David A Bloom Professor of Urology, Director, Division of Minimally Invasive Urology, Department of Urology, University of Michigan Medical Center; William J Cromie, MD, MBA, President and Chief Executive Officer, Health Care, Capital District Physicians' Health Plan
Author and Editor Disclosure
Synonyms and related keywords:
megaureter, primary megaureter, ectopic ureter, ureteral duplication, ureterocele, vesicoureteral reflux, VUR, ureterovesical junction anomalies, ureteral ectopia, urinary tract infection, UTI, bladder outlet obstruction, BOO, megaureter-megacystis syndrome, hydroureteronephrosis, voiding cystourethrogram, VCUG
Developmental abnormalities of the ureter encompass a wide range of disorders. Ureteral anomalies are a common cause of morbidity in children and frequently require surgical intervention.
Interestingly, Leonardo da Vinci and Galen were the first to begin to recognize the importance of the ureterovesical junction (UVJ) and to identify vesicoureteral reflux. Semblinow's 1883 animal experiments renewed enthusiasm for the study of reflux and began the modern era of research to clarify the anatomy, function, and pathophysiology of UVJ anomalies.
Problem
- Duplex (duplicated) system
- The duplex system is a renal unit in which the kidney has 2 pelvicaliceal systems. A patient with a duplication anomaly may have a single ureter with a duplicated collecting system, bifid ureters (partial or incomplete duplication), or 2 ureters that empty separately into the bladder (complete duplication). The upper ureter is more likely to be associated with ectopic insertion, ureterocele, and/or obstruction, whereas the lower ureter is frequently associated with vesicoureteral reflux (VUR).
- The upper (lower) pole is one of the components of the duplex kidney. The upper (lower)-pole ureter drains the upper (lower) pole of a duplex kidney.
- Caudal or medial ectopia describes the ureteral orifice when located at the proximal lip of the bladder neck or beyond.
- Ectopic ureter
- Ectopic ureter occurs when the ureter drains to an abnormally located (ectopic) orifice.
- Bilateral single-system ureteral ectopia is rare and usually coexists with a multitude of other urinary tract abnormalities (eg, VUR, renal dysplasia, rudimentary bladder development).
- Megaureter
- A megaureter is a wide ureter.
- Megaureters may be classified as obstructed, refluxing, obstructed and refluxing, and nonobstructed/nonrefluxing.
- Ureterocele
- A ureterocele is a congenital saccular dilatation of the distal segment of the ureter.
- This anomaly usually involves the upper pole of a duplex system. The ureter inserts ectopically (ectopic ureterocele) but may involve a single system. In this case, the ureter usually inserts within the bladder (orthotopic ureterocele).
- Ureteroceles may be associated with obstruction and VUR.
- Vesicoureteral reflux
- VUR is retrograde passage of urine. Reflux-induced renal injury is usually caused by the association of VUR with urinary tract infection (UTI).
- Reflux-induced renal injury was generally thought to occur primarily in children younger than 2 years. Recent theories suggest, however, that the risk of renal injury from VUR may occur in individuals well beyond this age.
- Reflux may also cause renal injury in the absence of UTI because of pressure effects, especially when VUR is secondary to posterior urethral valves (PUV) or bladder outlet obstruction (BOO).
- Cases involving infants with significant renal injury in the absence of BOO, neurogenic bladder (NGB), or UTI are encountered.
- Reflux-induced renal injury may range from clinically silent focal scars to generalized scarring and renal atrophy (reflux nephropathy), which may lead to morbidity during pregnancy, renin-mediated hypertension, renal insufficiency, and even end-stage renal disease.
Frequency
- Ureteral duplication
- Ureteral duplication is the most common anomaly of the urinary tract.
- Incidence is as high as 8% in children being evaluated for UTI.
- Incomplete ureteral duplication is observed in approximately 1 in 25 individuals.
- Complete duplication is present in approximately 1 in 500 individuals.
- Complete duplication on one side results in a 40% chance of a complete duplication abnormality on the other side.
- Approximately 10% of siblings may also be affected by complete duplication.
- Ectopic ureters
- Ectopic ureters occur in 0.025% of the population.
- Approximately 10% are bilateral.
- Ectopic ureters occur more frequently in females than in males (by a ratio of 6:1).
- In females, more than 80% of ectopic ureters drain duplicated systems. In males, most ectopic ureters drain a single system.
- Approximately 80% of all ectopic ureters drain the upper pole of a duplex kidney.
- In males, the ureters may terminate at the bladder neck/prostatic urethra (48%), seminal vesicle (40%), ejaculatory duct (8%), vas deferens (3%), or epididymis (0.5%).
- In females, the ureters may terminate at the bladder neck/urethra (35%), vestibule (30%), vagina (25%), or uterus (5%).
- Megaureters
- Bilateral involvement is present in about 20% of patients with primary obstructed megaureters.
- Primary obstructed megaureter has a male-to-female ratio of nearly 4:1.
- The left side is more often affected than the right.
- Ureterocele
- Incidence is approximately 1 in 4000 children.
- Approximately 80% occur in females.
- Approximately 10% are bilateral.
- Approximately 80% are associated with duplicated collecting systems with single system ureteroceles being more common in males and adults.
- Vesicoureteral reflux
- Incidence in otherwise healthy children is approximately 1%.
- The incidence is approximately 40% in patients undergoing evaluation for UTI.
- The reported risk of reflux in a sibling is 27-43%.
- Approximately 66% of the offspring of women with reflux also have VUR.
Etiology
A ureteral bud, the early precursor of the ureter, branches off from the caudal portion of the wolffian (mesonephric) duct between the fourth and sixth week of gestation. The cranial portion of the ureteral bud joins with the metanephric blastema and begins to induce nephron formation. The bud subsequently branches into the renal pelvis and the calyces and induces nephron formation. Caudally, the mesonephric duct (along with the ureteral bud) is incorporated into the cloaca as it forms the bladder trigone. Alterations in bud number, position, or time of development result in ureteral anomalies.
Early branching of a single ureteral bud results in incomplete (partial) duplication, with a single ureteral orifice and bifid proximal ureters. An accessory ureteral bud creates complete duplication, with the upper ureter usually protruding into the bladder more medially and inferiorly than the lower ureter. Ectopic termination of a single system or of the ureter of a duplex system is the result of the high (cranial) origin of the ureteral bud from the mesonephric duct. Because of the delayed incorporation of the ureteral bud into the bladder, the resulting position of the ureteral orifice is more caudal and medial.
The function of the ureter is to effectively transport the urinary bolus from the minor calyces to the urinary bladder at acceptably low pressures. The efficiency of this task depends on adequate coaptation of the ureteral wall to propel the urinary bolus. If the ureter fails to propagate the peristaltic wave, the static urine distends the upper urinary tract and reduces luminal coaptation. Other factors that affect ureteral transport are urinary volume and bladder pressure.
Pathophysiology
Megaureters
The term megaureter refers to an enlarged ureter. The 4 categories of megaureters are refluxing, obstructing, refluxing/obstructing, and nonrefluxing/nonobstructing. Each category is further divided into primary or secondary, based on either intrinsic or extrinsic causes for their appearance.
- Primary obstructed megaureter is most commonly caused by an adynamic juxtavesical segment of the ureter that fails to effectively propagate urine flow.
- Secondary obstructed megaureter occurs usually when ureteral dilatation is the result of a functional ureteral obstruction associated with elevated bladder pressures secondary to PUV or an NGB that impedes ureteral emptying.
- Primary refluxing megaureter is associated with severe VUR that alters ureteral efficiency by ureteral distention and by augmentation of the volume of urine that must be moved back into the bladder. The megaureter-megacystis syndrome is an extreme form of the primary refluxing megaureters in which massive reflux prevents effective bladder emptying because urine is passed back and forth between the ureters and bladder.
- Secondary refluxing megaureter occurs secondary to PUV and NGB when elevated bladder pressures cause decompensation of the UVJ.
- Primary nonrefluxing/nonobstructed megaureter is diagnosed when no evidence of obstruction or reflux can be demonstrated (diagnosis of exclusion).
- Secondary nonrefluxing/nonobstructed megaureter occurs secondary to diabetes insipidus, in which high urinary flow rates may overwhelm the maximum transport capacity of the ureter by peristalsis or as the result of ureteral atony accompanying a gram-negative UTI.
- Primary refluxing obstructed megaureter occurs in the presence of an incompetent VUJ that allows reflux through an adynamic distal segment.
Vesicoureteral reflux
A sufficient tunnel length of the submucosal ureter is the most important component of a competent UVJ, which provides a predominantly passive valve mechanism for ureteral compression and prevents retrograde urine passage. Factors that affect marginal tunnel pressure, causing either primary or secondary reflux, include the loss of UVJ compliance (during UTI), structural weaknesses in the detrusor floor (bladder diverticulum, ureterocele), or excessively high intravesical pressure resulting from neurovesical dysfunction or BOO. Reflux resulting from a congenitally deficient UVJ is referred to as primary reflux; reflux resulting from a BOO or NGB is referred to as secondary reflux.
Clinical
No specific clinical signs are associated with ureteral anomalies. Most children present with an abnormal finding on routine prenatal ultrasound before associated symptoms or infection develops. Some patients present with UTI, cyclic abdominal pain, abdominal mass, and hematuria. Patients may present with a cystic mass at the urethral meatus representing a prolapsed ureterocele. In other patients, the diagnosis is incidental after imaging studies for unrelated symptomatology.
Ureteral anomalies may be discovered during the evaluation of a patient with hypertension, proteinuria, or even renal insufficiency (in rare cases of severe bilateral anomalies).
Approximately 50% of females with ectopic ureters present with constant urinary incontinence or vaginal discharge. Consider ectopic ureteral insertion in prepubertal boys who have a history of recurrent epididymitis. Postpubertal males with ectopic ureters most commonly present with complaints of chronic prostatitis and painful intercourse and ejaculation. In males, incontinence is never due to an ectopic ureter because the ectopic ureteral orifice never inserts distal to the external urethral sphincter.
Megaureter
- Increasing hydroureteronephrosis
- Decrease in renal function of involved kidney
- Development of UTI or recurrent pain
Ureterocele
- Obstruction
- Urosepsis or compromised renal function may necessitate urgent decompression prior to definitive surgical reconstruction.
Vesicoureteral reflux (absolute indications)
- Progressive renal injury
- Documented failure of renal growth
- Breakthrough pyelonephritis
- Intolerance or noncompliance with antibiotic suppression
- Informal parental request
Vesicoureteral reflux (relative indications)
- Pubertal age
- High-grade (IV or V) VUR
- Failure to resolve with 4-5 years of antibiotic suppression
Ureters are paired muscular tubes that run from the renal pelvis to the bladder and travel through retroperitoneal connective tissue in a serpentine fashion. The ureters run through 3 natural areas of narrowing: the ureteropelvic junction, the crossing of the iliac vessels, and the UVJ. From the renal pelvis to the iliac vessels, the ureter is referred to as the abdominal ureter. From the great vessels to the bladder, the ureter is called the pelvic ureter.
The UVJ may be divided into 3 sections: the terminal portion (juxtavesical ureter), the intramural portion, and the submucosal portion (under the bladder mucosa).
The presence of an acute UTI, especially with bullous edema of the bladder mucosa, may be a contraindication to definitive reconstruction. Urinary diversion (eg, ureterostomy, vesicostomy) or drainage may be necessary.
Lab Studies
- Urinalysis and urine culture are important in evaluating any young child with an unexplained fever, and the diagnosis of UTI should prompt further radiological evaluation to identify urologic structural anomalies.
- When identifying structural anomalies in the presence of febrile illness, it is essential to evaluate the patient for a UTI and to provide early treatment to minimize the risk of renal injury.
Imaging Studies
- Renal and bladder ultrasound is a first-line imaging study to evaluate the upper (eg, duplication, dilatation of collecting system, character or thickness of the renal parenchyma) and lower urinary tract (eg, bladder wall thickness, ureterocele, diverticulum, posterior urethral dilatation, degree of bladder emptying).
- Cyclic voiding cystourethrogram (VCUG) is an essential evaluation of the lower urinary tract (eg, VUR, diverticulum, ureterocele, bladder trabeculation, bladder emptying, urethral anatomy during voiding).
- Diuretic nuclear renography is an excellent study to objectively establish differential renal function and to evaluate the drainage efficiency of the dilated collecting system (ie, washout times).
- Intravenous pyelogram (IVP) is a useful study, although it has been largely replaced by ultrasound and nuclear renography. IVP delineates anatomy (ie, dilatation of collecting system, renal or ureteral displacement, bladder wall characteristics) and provides subjective estimation of relative renal function.
- MRI is an excellent anatomical study to evaluate the rare cases when dysplastic nonfunctioning ectopic renal moieties or ectopic ureteral insertion are suspected.
Other Tests
- Urodynamic studies (eg, flow study, cystometrogram) assess voiding and bladder functional characteristics that are essential in the evaluation of a suspected NGB.
Diagnostic Procedures
- Cystoscopy, vaginoscopy, and retrograde pyelogram are endoscopic procedures that allow direct visualization of the genital and lower urinary tracts and may include radiographic visualization of the upper urinary tract (eg, retrograde pyelogram).
- Pressure-perfusion studies (ie, Whitaker test) measure differential pressures of the renal pelvis and the bladder. This invasive study, which requires percutaneous renal access, may be useful in evaluating equivocal urinary tract obstruction.
Histologic Findings
- Ureteral ectopia
- Single-system ureteral ectopia reveals widespread renal dysplasia in 90% of affected kidneys.
- Duplicated-system ureteral ectopia reveals renal dysplasia in approximately 50% of affected renal moieties.
- Megaureters
- Light microscopy of megaureters demonstrates a predominance of circular smooth muscle; muscle fiber hypoplasia and atrophy, with collagen deposits separating the muscle cells; and mural fibrosis with scant muscle fibers.
- Electron microscopy of megaureters demonstrates increased collagen deposition within the adynamic segment.
Medical therapy
Increasing experience shows that a considerable number of children with VUR or megaureters without reflux or obstruction may demonstrate improved renal function on radiography, without surgical intervention. Nonoperative treatment mandates close follow-up care in patients with VUR or nonobstructed/nonrefluxing megaureters.
Nonoperative management of VUR and nonobstructed primary megaureter includes antimicrobial suppression, symptomatic voiding dysfunction treatment, and regular imaging studies to assess renal growth, renal scarring, and possible resolution of pathology.
In the absence of obstruction and/or VUR, ureteral duplication anomalies require no specific therapy.
Surgical therapy
Megaureter Megaureter secondary to severe VUR or obstruction is usually managed with ureteral reimplantation. Reimplantation techniques are similar to those used for correcting primary VUR. Mobilize the megaureter via an intravesical, extravesical, or combined approach. Reduce ureteral caliber by excising the distal redundant ureter (Hendren technique) or plication (Kalicinski technique, Starr technique) to achieve a satisfactory antireflux mechanism. Occasionally, the function of the kidney drained by a megaureter is severely impaired, and nephroureterectomy may be necessary. Ureteral duplication Ureteral duplication alone requires no specific intervention. Duplication anomalies with associated pathology (eg, VUR, obstruction), however, require appropriate medical therapy and, possibly, surgical correction. Ureteral ectopia
- Single system
- If an ectopic ureter is associated with a single system, the kidney is usually dysplastic or poorly functioning. The recommended treatment is nephrectomy with partial or total ureterectomy. If the involved kidney is functioning satisfactorily, the recommended treatment is ureteral reimplantation.
- In rare instances of bilateral single-system ectopic ureters, when the bladder capacity is actually adequate for urination, bilateral ureteral reimplantation is performed; if the bladder neck is poorly developed in association with the ureteral ectopia, bladder neck reconstruction (Young-Dees-Leadbetter bladder neck plasty) may be necessary.
- Duplex system
- Treatment depends on the function of the involved upper pole and whether VUR is present. If function is adequate, a ureteropyelostomy (upper-pole ureter to lower-pole renal pelvis) or ureteroureterostomy (upper-pole ureter to lower-pole ureter) is performed.
- In patients with a functioning upper-pole system and coexisting lower-pole VUR, a common sheath ureteral reimplantation is performed. If the upper-pole moiety is nonfunctional, a partial nephroureterectomy is performed and the upper-pole ureter is removed to the pelvic brim. If patients have coexisting upper-pole VUR, the ureteral stump should be ligated to prevent retroperitoneal extravasation with each void.
Ureterocele Treatment of the ureterocele is based upon relief of obstruction. Endoscopic decompression may be used in cases in which urgent decompression is required (eg, urosepsis, severe compromise in renal function), or it may be used as definitive therapy in the case of a single-system intravesical ureterocele. Endoscopic decompression in cases of ectopic ureterocele demonstrates a success rate of only 10-40%; therefore, surgical reconstruction is often required. Options for reconstruction include ureteropyelostomy, excision of ureterocele and ureteral reimplantation, or upper-pole heminephrectomy with partial ureterectomy and ureterocele decompression. In patients with a single-system ureterocele and an associated nonfunctioning kidney, a nephroureterectomy may be performed. Vesicoureteral reflux Because the submucosal ureter tends to lengthen with age, the ratio of tunnel length to ureteral diameter also increases, and the propensity for reflux may disappear. Nonoperative management of VUR, which is successful in most patients, requires preventing UTI with suppressive antibiotics, treating symptomatic voiding dysfunction, and maintaining strict long-term surveillance. In general, ureteral reimplantation has excellent results (>95% success rate). Although the transvesical approach is commonly used, the extravesical approach (detrusorrhaphy), which preserves the integrity of the bladder lumen and does not require a ureteral anastomosis, eliminates postoperative hematuria, minimizes bladder spasms, decreases the risk of postoperative obstruction, and shortens the hospital stay.
Preoperative details
The goals of the preoperative evaluation of the possible ureteral anomaly are as follows:
- Detailed delineation of upper and lower urinary tract anatomy
- Assessment of differential function of each of the renal moieties
- Detection of the presence of anatomical or functional obstruction or VUR
- Evaluation of bladder function
Intraoperative details
The principles of successful ureteral reconstruction are as follows:
- Adequate ureteral exposure and mobilization with meticulous preservation of blood supply
- Gentle handling of the tissue, and protection of the contralateral ureteral orifice
- With ureteral reimplantation, a submucosal tunnel with a length-to-ureteral diameter ratio of 5:1 to create an adequate valve mechanism to prevent VUR
Follow-up
Follow-up care includes renal ultrasound to assess renal growth and the presence of renal scarring or hydronephrosis. Suppressive antibiotics are discontinued during the postoperative period. Parents are counseled that urinalysis and urine culture are still indicated if their child becomes symptomatic (eg, dysuria, flank pain, hematuria) and that, although their child is at a much smaller risk for kidney infection, bladder infections may still occur. Periodic evaluation of voiding symptoms and bladder function are also included in follow-up care.
Complications of ureteral reimplantation are uncommon. The most common technical complications are ureteral obstruction, persistent reflux, and diverticula formation.
Ureteral reimplantation for megaureter repair is a very safe, reproducible, and successful procedure. The major complications are the development of ureteral obstruction (2-5%) or VUR (approximately 10%). Ureteral obstruction is most likely the result of ureteral ischemia and subsequent fibrosis of the tapered segment. Initial management of this complication is percutaneous dilatation of the stricture, but many such instances ultimately require open surgical revision. If postoperative VUR is encountered, a reasonable treatment option is observation and antibiotic prophylaxis because many reflux cases resolve spontaneously.
In addition, VUR is more likely to recur following reimplantation in cases in which bladder pressures are elevated (eg, patients with untreated neuropathic bladders or voiding dysfunction). A careful assessment of voiding symptoms and a low threshold for urodynamic studies are crucial in the evaluation of patients with recurrent VUR.
The outcome of ureteral anomalies chiefly depends on the presence or absence of obstruction and/or infection, which can lead to renal injury. In the absence of these, no treatment may be necessary, especially in the case of isolated ureteral duplication anomalies, low-grade VUR, the small orthotopic ureterocele, and nonobstructed, nonrefluxing primary megaureter. With respect to primary megaureters, as in the case of VUR, spontaneous resolution is not rare.
Cases of high-grade VUR are less likely to resolve and more likely to put the kidney at risk of scarring because of infection. Prevention of infection is essential to minimize the risk of renal damage; therefore, suppressive antibiotics are usually used. In the case of the obstructed primary megaureter, spontaneous resolution is less likely to occur. Some authors have reported up to an 84% failure rate for nonoperative therapy. As with obstructive ureteroceles, treatment to relieve obstruction optimizes preservation of renal function.
Efforts to use a minimally invasive approach to treatment of VUR are under study. These approaches may include different materials for endoscopic subtrigonal injection or may implement laparoscopic techniques into standard surgical procedures to correct VUR.
In addition, because of the very high success rate of ureteral reimplantation, the role of postoperative imaging other than renal ultrasound is under discussion. Many surgeons have eliminated the postoperative voiding cystogram from their routine except in selected high-risk patients.
| Media file 1:
Intravenous urogram demonstrating left primary megaureter in comparison to normal right collecting system. |
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| Media file 2:
Ultrasound image of a normal right kidney in a child with a febrile urinary tract infection. Image courtesy of Steven Kraus, MD, Cincinnati, Ohio. |
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| Media file 3:
Ultrasound image of the same patient (in Picture 2), demonstrating that the left kidney has a duplex collecting system. Note the lower-pole hydronephrosis. Image courtesy of Steven Kraus, MD, Cincinnati, Ohio. |
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| Media file 4:
Voiding cystourethrogram from the same patient (in Picture 2), demonstrating right vesicoureteral reflux into a single system and left vesicoureteral system into the lower pole of a duplicated system. Note the deficiency of upper-pole calyces on the left side and the "drooping lily" appearance of the left lower-pole system, which suggest the duplication anomaly in this case. Image courtesy of Steven Kraus, MD, Cincinnati, Ohio. |
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| Media file 5:
Voiding cystourethrogram that illustrates a right ureterocele characterized by the round filling defect at the right bladder base. Image courtesy of Steven Kraus, MD, Cincinnati, Ohio. |
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Media type: X-RAY
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Megaureter and Other Congenital Ureteral Anomalies excerpt Article Last Updated: Feb 9, 2007
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