Duplicated Ureters

Duplicated ureters are congenital anomalies in which a kidney develops two ureteric drainage pathways instead of the usual single ureter. Duplication may be complete, with two separate ureters entering the urinary tract independently, or incomplete, with two proximal ureteric channels joining before reaching the bladder.

Ureteral duplication is closely related to development of the ureteric bud and is commonly associated with duplication of the renal collecting system. The resulting kidney is often described as a duplex kidney or as having a duplex collecting system.

Normal Embryological Development

The permanent kidney, or metanephros, develops through interaction between the ureteric bud and metanephric mesenchyme.

The ureteric bud normally arises as a single epithelial outgrowth from the mesonephric duct near its entry into the developing cloaca.

Ureteric Bud

The ureteric bud grows into the metanephric mesenchyme and undergoes repeated branching.

Its derivatives form the collecting portion of the permanent kidney.

Derivatives of the Ureteric Bud

• Ureter
• Renal pelvis
• Major calyces
• Minor calyces
• Collecting ducts and collecting tubules

Metanephric Mesenchyme

The surrounding metanephric mesenchyme gives rise primarily to the nephron components of the kidney.

Normal renal development therefore requires coordinated interaction between the ureteric bud and metanephric tissue.

Embryological Basis of Ureteral Duplication

Duplicated ureters develop when the normal pattern of ureteric bud formation or branching is altered.

The precise developmental event determines whether the duplication is complete or incomplete.

Incomplete Duplication

Incomplete ureteral duplication usually results when a single ureteric bud divides prematurely before reaching or while interacting with the metanephric mesenchyme.

The resulting branches induce separate portions of the developing collecting system but remain connected proximally to a common distal ureteric pathway.

Bifid Ureter

Incomplete duplication is often called a bifid ureter.

Two ureteric channels arise from the duplicated collecting system and subsequently unite at a variable level before entering the bladder through a single distal ureter.

Site of Fusion

The two branches of a bifid ureter may unite at different levels along their course.

The point of union may occur relatively close to the kidney or farther distally near the urinary bladder.

Complete Duplication

Complete ureteral duplication generally results from the development of two separate ureteric buds from the mesonephric duct.

Each bud interacts with the metanephric mesenchyme and forms a separate collecting system and ureter.

Two Separate Ureters

In complete duplication, two ureters descend from the duplex kidney without joining one another.

Each ureter has its own distal insertion, although one of the openings may be ectopic rather than normally positioned within the bladder trigone.

Duplex Collecting System

A duplex collecting system consists of two drainage systems within a single kidney.

The kidney is commonly divided functionally into an upper pole moiety and a lower pole moiety, each drained by its corresponding ureteric system.

Upper Pole Moiety

The upper portion of a duplex kidney drains through the ureter associated with the upper collecting system.

In complete duplication, this ureter tends to have a more inferior and medial insertion than the ureter draining the lower pole.

Lower Pole Moiety

The lower portion of the duplex kidney drains through the second ureter.

Its ureteric orifice tends to lie more superiorly and laterally within the bladder than the opening of the upper pole ureter.

Weigert-Meyer Relationship

In a typical completely duplicated collecting system, the ureters follow the Weigert-Meyer relationship.

The ureter draining the upper renal moiety inserts more inferiorly and medially, while the ureter draining the lower renal moiety inserts more superiorly and laterally.

Crossing of the Ureters

Although the upper pole collecting system originates superiorly within the kidney, its ureter commonly crosses the lower pole ureter during descent.

This developmental arrangement explains why the upper pole ureter reaches the more inferior and medial distal insertion.

Comparison of Duplex Ureters

Feature	Upper Pole Ureter	Lower Pole Ureter
Renal drainage	Upper moiety	Lower moiety
Typical distal position	Inferior and medial	Superior and lateral
Common complication	Obstruction or ureterocele	Vesicoureteral reflux
Ectopic insertion	More commonly associated	Less commonly associated

Ectopic Ureter

An ectopic ureter is a ureter that terminates outside its normal position within the urinary bladder.

In a completely duplicated system, ectopic insertion most commonly involves the ureter draining the upper renal moiety.

Ectopic Insertion in Females

In females, an ectopic ureter may open into structures distal to or outside the normal bladder outlet.

Possible sites include the urethra, vestibule, or vagina, depending on the developmental anatomy.

Ectopic Insertion in Males

In males, ectopic ureters may terminate in structures derived from or associated with the mesonephric duct system.

Possible insertion sites include the prostatic urethra, seminal vesicle, or ejaculatory duct region.

Relationship to Continence

The clinical effect of an ectopic ureter depends strongly on whether its opening lies proximal or distal to the continence mechanism.

An ectopic opening distal to the external urethral sphincter can produce continuous urinary leakage despite otherwise normal bladder emptying.

Ureterocele

A ureterocele is cystic dilation of the distal intravesical portion of a ureter.

In duplicated collecting systems, ureteroceles are particularly associated with the ureter draining the upper pole moiety.

Upper Pole Obstruction

An ectopic or ureterocele-associated upper pole ureter may become obstructed.

Obstruction can produce dilation of the ureter and collecting system and may impair development or function of the upper renal moiety.

Hydroureter

Hydroureter refers to dilation of the ureter resulting from impaired drainage or other abnormalities of urinary flow.

A duplicated ureter affected by distal obstruction may become enlarged along part or all of its course.

Hydronephrosis

Hydronephrosis is dilation of the renal collecting system resulting from impaired urinary drainage.

In a duplex kidney, hydronephrosis may selectively affect one moiety depending on which ureter is obstructed.

Vesicoureteral Reflux

Vesicoureteral reflux is retrograde movement of urine from the bladder into the ureter and potentially toward the kidney.

In complete duplication, reflux more commonly involves the ureter draining the lower renal moiety.

Lower Pole Reflux

The more superior and lateral insertion of the lower pole ureter may be associated with an inadequate intramural ureteric course.

This can reduce the effectiveness of the normal anti-reflux mechanism at the ureterovesical junction.

Upper and Lower Moiety Complications

Renal Moiety	Typical Associated Problem
Upper pole	Ectopic insertion, ureterocele, or obstruction
Lower pole	Vesicoureteral reflux

Urinary Tract Infection

Many duplicated ureters are asymptomatic, but abnormal urinary drainage can predispose some individuals to recurrent urinary tract infections.

Stasis, reflux, or obstruction can facilitate persistence or ascent of infection.

Incomplete Duplication and Urine Flow

In a bifid ureter, the two branches converge before reaching the bladder.

The shared distal pathway usually enters the bladder through a single ureteric orifice.

Ureteroureteral Reflux

In some incompletely duplicated systems, urine can pass from one branch of the duplicated ureter into the other rather than moving directly toward the bladder.

This phenomenon is sometimes described as yo-yo reflux or ureteroureteral reflux.

Unilateral Duplication

Ureteral duplication may affect only one kidney.

In unilateral duplication, the opposite urinary tract may have completely normal anatomy.

Bilateral Duplication

Duplication can occur on both sides, producing duplicated collecting systems involving both kidneys.

The degree and type of duplication do not necessarily have to be identical on the two sides.

Partial and Complete Forms

Feature	Incomplete Duplication	Complete Duplication
Typical developmental basis	Premature division of one ureteric bud	Two ureteric buds develop
Number of distal ureters	One after fusion	Two separate ureters
Bladder openings	Usually one	Usually two separate openings or one ectopic termination
Common term	Bifid ureter	Complete ureteral duplication

Renal Parenchyma

A duplex collecting system does not necessarily mean that two completely separate kidneys are present.

Both collecting systems are usually contained within a single renal mass, although the upper and lower moieties may differ in size and function.

Renal Function

Renal function may remain normal when duplicated ureters drain freely and are not associated with reflux, obstruction, infection, or significant dysplasia.

When complications occur, function may be reduced selectively within the affected renal moiety.

Upper Pole Dysplasia

Severe obstruction of the upper pole collecting system during development can be associated with abnormal development of the corresponding renal tissue.

The upper moiety may therefore be poorly functioning in some complicated duplex systems.

Clinical Presentation

Duplicated ureters are frequently discovered incidentally and may never produce symptoms.

When clinically significant abnormalities are present, presentation depends on the associated drainage problem.

Possible Clinical Findings

• Recurrent urinary tract infections
• Hydronephrosis
• Hydroureter
• Vesicoureteral reflux
• Ureterocele
• Ectopic ureter
• Continuous urinary leakage with certain ectopic insertions
• Reduced function of an affected renal moiety

Prenatal Detection

Some duplex collecting systems are identified during prenatal imaging, particularly when associated with dilation of part of the collecting system.

Hydronephrosis or a ureterocele may provide clues to the underlying duplicated anatomy.

Ultrasound

Ultrasound can demonstrate duplication of the collecting system and detect associated hydronephrosis, ureteral dilation, or ureterocele.

It is commonly used for initial assessment because it does not require ionizing radiation.

Voiding Cystourethrography

Voiding cystourethrography can be used when vesicoureteral reflux is suspected.

It demonstrates retrograde passage of contrast from the bladder into the ureter and collecting system during bladder filling or voiding.

Cross-Sectional Imaging

Computed tomography and magnetic resonance imaging can delineate complex renal and ureteric anatomy.

These modalities can help identify the course of duplicated ureters, their distal insertion, associated obstruction, and the anatomy of individual renal moieties.

Functional Imaging

Renal functional studies can assess the relative contribution of different portions of a duplex kidney.

This information may be important when treatment decisions depend on whether an obstructed or refluxing moiety retains useful function.

Management Considerations

An uncomplicated duplicated ureter may require no intervention.

Management of symptomatic cases is directed toward the specific anatomical problem, such as obstruction, reflux, ectopic drainage, recurrent infection, or impaired function of a renal moiety.

Surgical Anatomy

Recognition of duplicated ureters is important during abdominal, pelvic, retroperitoneal, and urological surgery.

An unrecognized additional ureter can be at risk during procedures performed near the normal ureteric course.

Relationship to Ureteric Bud Development

The anatomy of duplicated ureters illustrates the importance of the timing and number of ureteric buds during urinary system development.

Early splitting of one bud tends to produce incomplete duplication, whereas formation of two distinct buds can produce complete duplication.

Developmental Comparison

Developmental Event	Result
Normal single ureteric bud	Single ureter and collecting system
Premature branching of one bud	Incomplete duplication or bifid ureter
Two separate ureteric buds	Complete ureteral duplication

Distinction from Supernumerary Kidney

A duplex kidney should not be confused with a supernumerary kidney.

In a duplex system, duplicated collecting structures are generally contained within a single renal mass, whereas a supernumerary kidney represents an additional distinct renal organ with its own parenchyma and anatomical relationships.

Key Anatomical Features

• Duplicated ureters result from altered ureteric bud development.
• Duplication may be complete or incomplete.
• Incomplete duplication usually results from premature division of a single ureteric bud.
• Incomplete duplication is commonly called a bifid ureter.
• Complete duplication generally results from formation of two separate ureteric buds.
• A completely duplicated system contains two separate ureters.
• Duplicated ureters are commonly associated with a duplex renal collecting system.
• The duplex kidney can be divided into upper and lower renal moieties.
• The upper pole ureter typically inserts inferior and medial to the lower pole ureter.
• The lower pole ureter typically inserts more superiorly and laterally.
• This characteristic arrangement is described by the Weigert-Meyer relationship.
• The upper pole ureter is more commonly associated with ectopic insertion, ureterocele, and obstruction.
• The lower pole ureter is more commonly associated with vesicoureteral reflux.
• Duplication may be unilateral or bilateral.
• Many duplicated collecting systems remain asymptomatic.

Clinical Importance

Duplicated ureters are important congenital anomalies because the abnormal arrangement of the ureteric drainage system can alter urine flow even when the renal parenchyma itself is largely preserved. Complete and incomplete duplication have different embryological origins and different distal anatomical configurations.

The characteristic relationship between the two ureters in complete duplication helps explain common complications. The upper pole ureter tends toward an inferior and medial insertion and may be associated with ectopia, ureterocele, and obstruction, while the lower pole ureter is more commonly associated with vesicoureteral reflux.

Understanding duplicated ureters provides the anatomical and embryological foundation for studying ureteric bud development, duplex kidneys, bifid ureters, the Weigert-Meyer relationship, ectopic ureters, ureteroceles, vesicoureteral reflux, hydronephrosis, and congenital abnormalities of the urinary collecting system.