Megaureter and Other Congenital Ureteral Anomalies

Megaureter and Other Congenital Ureteral Anomalies

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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 (VUR). 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.

Congenital ureteral anomalies include the following:

The duplex system is a kidney with two ureters. A patient with a duplication anomaly may have bifid ureters (partial or incomplete duplication) or two 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 more frequently associated with VUR.

The upper pole is one of the components of the duplex kidney. The upper pole ureter drains the upper pole of a duplex kidney. Similarly, the lower pole of the kidney is drained by the lower-pole ureter.

Caudal or medial ectopia describes the ureteral orifice when located at the proximal lip of the bladder neck or more distal.

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).

A megaureter is a wide ureter, greater than 7 mm in diameter. Megaureters may be classified into the following four categories:

A ureterocele is a congenital saccular dilatation of the distal segment of the ureter.

This anomaly most frequently involves the upper pole of a duplex system. If the ureterocele extends beyond the bladder into the urethra, it is considered an ectopic ureterocele. A ureterocele contained within the bladder is considered an orthotopic ureterocele.

Ureteroceles are often associated with obstruction and VUR.

VUR is retrograde passage of urine from the bladder into the ureter and/or kidney. Reflux-induced renal injury is usually caused by the association of VUR with urinary tract infection (UTI).

Reflux-induced renal injury was previously thought to occur primarily in children younger than 2 years. However, the risk of renal injury from pyelonephritis associated with VUR may occur in individuals well beyond this age.

Reflux may also be associated with regions of renal dysplasia or hypoplasia in the absence of UTI and is thought to be secondary to abnormal development.

Reflux that is secondary to high bladder pressures such as those occurring in patients with posterior urethral valves (PUV) or bladder outlet obstruction (BOO) is frequently associated with renal injury.

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.

Ureteral duplication

Ectopic ureters

Megaureters

Ureterocele

Vesicoureteral reflux

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 or in more severe cases it inserts into one of the Wolffian duct structures as noted above.

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 may affect ureteral transport include urinary volume and bladder pressure.

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, as follows:

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. 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 or neurogenic bladder 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.

A sufficient tunnel length of the submucosal ureter is the most important component of a competent UVJ, as it 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 neurogenic bladder is referred to as secondary reflux.

No specific clinical signs are associated with ureteral anomalies. In most cases the anomaly is an incidental finding on a routine prenatal ultrasound, and the condition can be addressed before symptoms or infection develop. Some patients present with UTI, abdominal mass, or hematuria. Children with primary megaureters may also present with cyclic abdominal pain/flank pain, or, less commonly, in acute pain crisis. [1] 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. Consideration of an ectopic ureteral insertion should be given in prepubertal boys with 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 ureter never inserts distal to the external urethral sphincter.

In megaureter, indications for surgical intervention are as follows:

In ureterocele, indications for surgical intervention are as follows:

In vesicoureteral reflux (VUR), absolute indications for surgical intervention are as follows:

Relative indications for surgical intervention in VUR are as follows:

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 iliac 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.

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Christopher S Cooper, MD, FACS, FAAP Professor with Tenure and Vice Chair, Department of Urology, Professor, Department of Pediatrics, Associate Dean for Student Affairs and Curriculum, Children’s Hospital of Iowa and University of Iowa, Roy J and Lucille A Carver College of Medicine

Christopher S Cooper, MD, FACS, FAAP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Medical Association, Phi Beta Kappa, Society for Pediatric Urology, Society for Fetal Urology, International Children’s Continence Society, American College of Surgeons, American Urological Association

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Mark Jeffrey Noble, MD Consulting Staff, Urologic Institute, Cleveland Clinic Foundation

Mark Jeffrey Noble, MD is a member of the following medical societies: American College of Surgeons, American Medical Association, American Urological Association, Kansas Medical Society, Sigma Xi, Society of University Urologists, SWOG

Disclosure: Nothing to disclose.

Edward David Kim, MD, FACS Professor of Surgery, Division of Urology, University of Tennessee Graduate School of Medicine; Consulting Staff, University of Tennessee Medical Center

Edward David Kim, MD, FACS is a member of the following medical societies: American College of Surgeons, American Society for Reproductive Medicine, American Society of Andrology, American Urological Association, Sexual Medicine Society of North America, Tennessee Medical Association

Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Endo, Avadel.

Angela M Arlen, MD Chief Resident, Department of Urology, University of Iowa, Roy J and Lucille A Carver College of Medicine

Angela M Arlen, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Urological Association, and Society of Women in Urology

Disclosure: Nothing to disclose.

Leslie Tackett McQuiston, MD, FAAP Assistant Professor of Surgery (Urology) Dartmouth Medical School; Staff Pediatric Urologist, Dartmouth-Hitchcock Hospital

Disclosure: Nothing to disclose.

Eugene Minevich, MD Assistant Professor, Department of Surgery, Division of Pediatric Urology, University of Cincinnati College of Medicine

Disclosure: Nothing to disclose.

Megaureter and Other Congenital Ureteral Anomalies

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