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Radiology > GENITOURINARY
Duplicated Collecting System
Article Last Updated: Feb 22, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia
Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England
Coauthor(s):
Muthusamy Chandramohan, MBBS, DMRD, FRCR, Special Registrar, Department of Radiology, Manchester Radiology;
Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute
Editors: Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Joshua A Becker, MD, Professor, Department of Radiology, New York University School of Medicine; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center
Author and Editor Disclosure
Synonyms and related keywords:
duplex collecting system, bifid collecting system, duplicate pyelocaliceal system, duplicate ureters, ureteropelvic obstruction, duplex kidney, duplex ureters, ureteral duplication, hydronephrosis, pyelonephritis, partial ureteric duplication, complete ureteric duplication, ectopic ureter
Background
Duplicated collecting systems (also known as duplex collecting systems) can be defined as renal units containing 2 pyelocaliceal systems that are associated with a single ureter or with double ureters. The 2 ureters empty separately into the bladder or fuse to form a single ureteral orifice. Duplex collecting systems can be unilateral or bilateral and can be associated with a variety of congenital genitourinary tract abnormalities. Most patients are asymptomatic, with genitourinary tract abnormalities being detected incidentally on imaging studies performed for other reasons. Symptomatic patients usually have complete ureteric duplication in which the ureters are prone to developing obstruction, reflux, and infection. Ureteropelvic obstruction is more common when a duplex kidney exists and can be inherited in an autosomal dominant pattern.1
See also the following related eMedicine topic:
Ureteral Duplication, Ureteral Ectopia, and Ureterocele
Pathophysiology
During embryogenesis, if a single ureteral bud bifurcates before bifurcation of the ampulla, a duplex kidney results, with a bifid pelvis or a bifid ureter. If 2 ureteral buds arise from the Wolffian duct, a duplex kidney with complete ureteral duplication results. The ureteral bud that is associated with the future lower pole separates first from the Wolffian duct, and the orifice progresses superiorly and laterally as a result of the urogenital sinus's growth. The common excretory duct, with the remaining ureter still attached, is taken up into the urogenital sinus. The orifice of the ureter that drains the upper pole opens medial and inferior to the orifice that drains the lower pole. A duplex kidney may be drained by a single ureter or by 2 ureters. In the latter case, the ureters can unite to form a single ureter or they can drain separately. Usually, the lower pole system is dominant; a large renal pelvis drains the lower pole through many calices. The upper pole pyelocaliceal system may have only a single calyx and a single infundibulum and drain directly into the ureter. Bifid ureters draining a duplex kidney join to form a single ureter, which can be intravesical (V-shaped) or, commonly, extravesical (Y-shaped). The ureter usually empties into the bladder. Rarely, a single proximal ureter divides distally to form an inverted Y. Usually, 2 ureteral orifices are observed on the same side; rarely, one of the ureters can be ectopic. In infrequent cases, the middle third of the ureter is duplicated, with a single proximal third and a single distal third. Double ureters remain completely separated, and in approximately 85% of patients, the upper pole ureter drains below and medial to the lower pole ureter (Weigert-Meyer rule). Certain potential abnormalities result from or are related to duplex systems. The following are well-known examples:
- Upper pole hydronephrosis from stenosis of the upper pole ureteral orifice
- Ectopic insertion of the upper pole ureter.
- Ectopic ureterocele of the upper pole ureter
- Reflux involving the lower pole, resulting from maldevelopment of the valve mechanism
See also the following related eMedicine topics:
Hydronephrosis and Hydroureter
Ureterocele
Frequency
United States
The overall incidence of duplex collecting systems appears to be the same in the United States as it is internationally.
International
Complete duplication of ureters occurs in 0.2% of live births; the chance of occurrence is 12% in first-degree relatives of persons with this condition. Bilateral duplication occurs in 15-40% of individuals with complete duplication. The prevalence of partial duplication found on urograms is 0.6%.2
Mortality/Morbidity
Most cases of duplex collecting system are detected incidentally; however, the incidence of ureteropelvic obstruction is increased with duplex kidney, hydronephrosis, and pyelonephritis in patients with complete ureteral duplication.1, 3
Race
No race predilection has been recorded.
Sex
No sex predilection is found among patients with bifid collecting systems and partial ureteric duplication. The presence of double ureters appears to be twice as common in females. Duplex kidney with uterus didelphys has been reported in identical twins.
Age
A duplex collecting system is a developmental anomaly, and patient age at presentation varies according to the type of abnormality. Patients with duplex kidney are usually asymptomatic, which means that, unless complications arise, duplex kidney is detected incidentally on imaging studies performed for other reasons. - Because of the widespread use of antenatal ultrasonography, duplex collecting systems are being diagnosed in utero.
- An ectopic ureter observed in a patient with complete ureteral duplication can present in the early stage, especially in female patients. This is because the ectopic ureter may insert below the sphincter or outside of the urinary tract (eg, vagina).
- Duplex ureter complicated by transitional cell carcinoma occurs in the elderly population.4
See also the following related topics in eMedicine:
Transitional Cell Carcinoma
Transitional Cell Carcinoma, Renal
Anatomy
When a single ureteral bud bifurcates before the ampulla bifurcates, a duplex kidney with a bifid renal pelvis or bifid ureter results.5 If 2 ureteral buds arise from the Wolffian duct, a duplex kidney with complete ureteral duplication ensues. The Committee on Terminology, Nomenclature, and Classification of the Section on Urology of the American Academy of Pediatrics suggests the use of the following terms in reference to duplex collecting systems6:
- Duplex kidney - The duplex kidney has a single renal parenchyma that is drained by 2 pyelocaliceal systems.
- Upper or lower pole - The poles represent one component of a duplex kidney.
- Duplex system - The kidney has 2 pyelocaliceal systems and is associated with a single ureter or with a bifid ureter (a partial duplication) or, in the case of a complete duplication, with 2 ureters (double ureters) that drain separately into the urinary bladder.
- Bifid system - Two pyelocaliceal systems join at the ureteropelvic junction (bifid pelvis), or 2 ureters join before draining into the urinary bladder (bifid ureters).
- Double ureters - Two ureters open separately into the renal pelvis superiorly and drain separately into the bladder or genital tract.
- Upper and lower pole ureters - Upper and lower pole ureters drain a duplex kidney's upper and lower poles, respectively.
Clinical Details
Presentation in patients with a duplex collecting system varies according to the type of anomaly. Patients with a duplex kidney are usually asymptomatic. Ureteropelvic junction obstruction is more common when a duplex kidney exists.7 Giant hydronephrosis in a duplex kidney can manifest as an extremely large abdominal and retroperitoneal mass; in rare cases, it can cause hypertension.8, 9, 10
The incidence of vesico-ureteric reflux, urinary tract infection, and parenchymal scarring is increased in patients with a duplex collecting system; patients can present with pyrexia and dysuria.11 Prolapsed ureterocele associated with a duplex ureter can cause urethral obstruction in males and females.12 Females who have complete duplication of the ureter along with ectopic insertion of the ureter can present with urinary incontinence. Males in such instances are always "dry," since the insertion is proximal to the sphincter.13
The results from a 2007 pediatric study indicated that the incidence of upper tract genitourinary anomalies is significantly higher in girls with congenital adrenal hyperplasia than it is in the general population (21.2% vs 2%-4%).14 These anomalies include vesico-ureteral reflux, hydronephrosis, and a duplex collecting system. This association represents a significant variation that in some patients can be used to guide therapeutic and prophylactic intervention, including surgical intervention and antibiotic prophylaxis to prevent urinary tract infections and preserve renal function.
See also the following related Medscape topic:
CME Therapy Insight: What Nephrologists Need to Know About Primary Vesicoureteral Reflux
Preferred Examination
- Plain radiography makes no major contribution to diagnosis. However, because a patient's duplex kidney is almost always longer than his/her nonduplex kidney, a renal mass may be apparent on a plain radiograph. Hydronephrotic upper or lower pole moiety in a duplex collecting system also can be observed as a renal mass.
- Excretory urographic findings are almost always diagnostic. Difficulty may arise when function is poor or absent in one of the moieties.
- If vesico-ureteral reflux exists, the presence of an ectopic ureter in a nonfunctioning moiety can best be demonstrated using a voiding cystourethrogram.11, 15
- Antegrade pyelography is useful in patients with hydronephrosis, to demonstrate the presence of a second ureter and to determine the level of ureteric termination.
- Arteriography is an invasive procedure and is no longer used to diagnose duplex collecting systems. However, it may occasionally be useful in planning nephron-sparing surgery.16
- Ultrasonography is a noninvasive and extremely useful examination, particularly in children. The ultrasonographic appearance of a duplex kidney is specific but not sensitive.17
- Computed tomography (CT) scanning with contrast is superior to ultrasonography and excretory urography in diagnosing the nubbin.18
- Magnetic resonance (MR) urography may be used as the primary diagnostic method for assessing a duplex ectopic ureter, as well as the complications associated with duplex kidneys.19, 20 Spatial resolution is a limiting factor.
- Scintigraphy is useful in the assessment of relative renal function and in the detection of renal scars.21
Limitations of Techniques
A patient's duplex kidney is almost always more elongated than his/her nonduplex kidney. The kidney may be enlarged when hydronephrotic and can be associated with rotational anomalies. - Plain radiographs can demonstrate a renal mass, which is a nonspecific finding.
- On excretory urography, an obstructed, nonfunctioning upper or lower pole may mimic a renal mass.
- Ultrasonographic findings provide excellent anatomic information but do not necessarily differentiate a bifid renal pelvis from a bifid ureter or from 2 complete ureters.
- On a CT scan, a large column of Bertin can mimic a duplex collecting system. However, CT scanning is valuable in the evaluation of an intravesical ureterocele, either orthotopic or ectopic.
- The availability of magnetic resonance imaging (MRI) is limited, the procedure is expensive, and it requires the sedation of patients with claustrophobia. However, MR urography is an extremely useful technique in patients who have the probability of an adverse reaction to radio-opaque contrast media.19
- Scintigraphy can reveal differential functioning. However, if the functioning is markedly depressed, imaging is limited.
Other Problems to Be Considered
Hypertrophied column of Bertin
Other renal masses22
Findings
- Plain radiography - In almost all patients, the duplex kidney is longer than the opposite, nonduplex kidney. In a duplex collecting system, hydronephrotic upper or lower pole moiety can be observed as a renal mass.
- Excretory urography
- A patient's duplex kidney is usually longer than his/her nonduplex kidney.
- The parenchymal thickness of one of the poles of the duplex kidney is less than that of the other pole.
- The calyces are asymmetric.
- An ectopic, upper pole ureteric insertion can produce a nonopacified segment. This mass effect results in the "drooping lily" sign with the depression of the lower pole pelvicaliceal system.
- If the lower pole of the duplex kidney is functioning poorly or not at all, the lower pole collecting system may not opacify, and no discernible parenchyma will surround it (nubbin sign). The kidney's appearance may consequently resemble that of a nonduplex kidney with a lower polar mass or renal infarct.
- A reduction in the number of calyces, the depiction of a portion of the collecting system, and the presence of a straight inferior border help to differentiate a duplex collecting system from a renal mass.
- Anomalies of the ureter, such as partial or complete ureteral duplication, may be demonstrated.
- Voiding cystourethrogram - The intravesical ectopic ureter of a nonvisualized moiety is better demonstrated using voiding cystourethrogram.
- Antegrade pyelography - In patients with hydronephrosis, antegrade pyelography is useful for demonstrating the presence of a second ureter and for determining the level of termination.
Degree of Confidence
Plain radiographic appearances in a duplex kidney are nonspecific. Urographic findings in a duplex system are almost always diagnostic in patients. Difficulty may arise when one of the moieties is poorly opacified or is not opacified at all. Reflux may occur into the ureter at only 1 pole, into both ureters in the same kidney, or, if the duplication is bilateral, into all 4 ureters.
False Positives/Negatives
On plain radiographs, depiction of a normal renal outline does not exclude a duplex collecting system. When a duplex kidney has a lower pole nubbin, the resulting image may give the impression that a lower pole mass is present. The upper pole moiety can simulate a renal/adrenal mass. Other causes of lower pole nubbins include parenchymal scarring, infection, and congenital anomalies. A second, nonfunctioning collecting system may not be depicted, leading to an erroneous determination that only a single collecting system exists. An absence of reflux does not exclude ureteral duplication.
Findings
Because the intervening renal parenchyma in a duplex kidney lacks a collecting system and major vessels, it is described as having a "faceless kidney" appearance. CT scanning can help to determine if an obstruction exists and can aid in assessing the renal parenchyma. CT scanning can also help to determine if the insertion of the duplex ureter is intravesical or extravesical. In addition, it can demonstrate the collecting system in the nubbin or the mass effect of tissue at the pole.18
Using 16-multidetector computed tomography (16-MDCT) scanning on 126 consecutive potential kidney donors, Raman and colleagues described and quantified renal anatomic variants and looked at the frequency of various findings associated with the renal parenchyma and with the collecting system.23 CT scan studies were produced prior to contrast injection, as well as after the intravenous power injection of nonionic contrast during the arterial, nephrographic, and excretory phases. The authors focused on the relevance of their results to the preoperative evaluation of potential laparoscopic renal donors.
Major and minor arterial and venous variants were confidently identified. Moreover, in 30% of the scanned kidneys, other parenchymal and urothelial abnormalities (for the most part, cysts and calyceal calcifications) were found. Additional relevant findings included focal infarcts, cortical scars, atrophic scarred kidney, and bilateral papillary necrosis. Among the identified urothelial variants were bilateral simple ureteroceles and a right-sided complete duplex collecting system. The authors concluded that MDCT has a potential use in the evaluation of possible laparoscopic renal donors.
Degree of Confidence
CT scanning is superior to ultrasonography and excretory urography in diagnosing the lower pole nubbin. In addition, the modality is helpful when function is poor or absent.
False Positives/Negatives
Diagnosing a lower pole polar nubbin is not always possible using CT scan findings, and an erroneous diagnosis may occur. Large cloisons (hypertrophied columns of Bertin) can simulate duplex kidneys on CT scans.24
Findings
MR urography can provide information similar to that of excretory urography when renal function is poor or absent. An ectopic ureter extending from a poorly functioning moiety of a duplex kidney, invisible on other imaging, may be observed with MR urography.19, 20
Ectopically inserted vaginal ureters generally present with continuous dribbling of urine. Jain describes a case of a young girl with a severe stenosis of the ectopically located ureteric orifice.25 When conventional imaging was used, the vaginal insertion of the ectopic ureter could not be seen. However, the collecting system, from the kidney to the point of ureteric insertion, appeared on an MR urogram. Engin and associates described the case of an adult male whose duplex ectopic ureter inserted into the prostatic urethra.26 Ultrasonography and MR urography depicted the collecting system from the kidney to the distal ureteral insertion.
Degree of Confidence
MR urography may be used as a primary diagnostic method in assessing a duplex ectopic ureter and complications associated with duplex kidneys.
False Positives/Negatives
The role of MR in imaging renal duplication anomalies is not yet clearly defined.
Findings
The duplex kidney appears as 2 central echo complexes with intervening renal parenchyma. Hydronephrosis at one pole is suggestive of a duplex kidney.17 Although hydronephrosis can occur at either pole, it is more common in the upper one. Occasionally, 2 distinct collecting systems and ureters can be observed on ultrasonographic images.
Degree of Confidence
The ultrasonographic appearance of a duplex kidney is specific but not sensitive. Differentiating an atrophied lower pole moiety of a duplex kidney (nubbin) from other renal masses is difficult.18
False Positives/Negatives
The nubbin of tissue from the atrophied lower pole of a duplex kidney cannot be confidently differentiated from other masses.
Findings
Duplex kidneys appear as 2 separate collecting systems on the same side of the body. Scintigraphy may demonstrate reflux up the ureter in a nonfunctioning duplex kidney with ureteral duplication.
Degree of Confidence
The presence of a duplex kidney and ureteral duplication, suggested by findings from excretory urographic or ultrasonographic images, can be confirmed with scintigraphy. The use of dimethyl succinic acid (DMSA) scanning to assess parenchymal function in a duplex kidney is of great value in the management of duplex kidney.21
False Positives/Negatives
Reflux of activity from the bladder can mimic cortical function in a nonfunctioning moiety. When DMSA scans are to be obtained in a pediatric patient with possible reflux, it is recommended that catheterization be performed prior to the study and that images be produced before the appearance of DMSA in the collecting system.
Findings
Invariably, 2 separate arteries arise, mostly independently from the aorta. Hydronephrosis of a moiety appears as a filling defect that displaces arterial branches.
Degree of Confidence
Arteriography is an invasive procedure and is no longer used to diagnose the presence of a duplex collecting system.
False Positives/Negatives
Filling defect due to hydronephrosis is a nonspecific finding.
Special Concerns
- Transitional cell carcinoma has been reported in patients with duplex collecting systems.
| Media file 1:
Line diagram shows development of complete ureteral duplication. |
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| Media file 2:
Excretory urography in a woman shows complete ureteral duplication on the right. The upper moiety ureter empties below and medial to the ureter of the lower moiety. Note the duplex collecting system on the left. |
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Media type: X-RAY
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| Media file 3:
Excretory urography in a man shows a blind-ending ureteric bud on the left, arising from the bladder. |
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Media type: X-RAY
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| Media file 4:
Excretory urography in an adult patient with bilateral complete ureteral duplication. |
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Media type: X-RAY
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| Media file 5:
Excretory urography in a patient with a duplex right kidney shows hydronephrosis of the lower moiety. |
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Media type: X-RAY
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| Media file 6:
Excretory urography in a man shows drooping of the right-sided calyces. No obvious mass is evident in the region of the right upper pole. |
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Media type: X-RAY
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| Media file 7:
Ultrasonographic scan of the bladder of a child with bilateral ureteral duplication demonstrates bilateral ureteroceles. |
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Media type: Ultrasound
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Duplicated Collecting System excerpt Article Last Updated: Feb 22, 2008
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