•Two pelvicalyceal systems join at the ureteropelvic junction (bifid pelvis), or two ureters join before draining into the urinary bladder (bifid ureters).

–Double/duplicated ureters (or collecting system):

•This is characterized by two ureters that drain separately into the bladder or genital tract.

•Two ureters open separately into the renal pelvis superiorly and drain separately into the bladder or genital tract.

•Upper and lower pole ureters drain a duplex kidney’s upper and lower poles, respectively.

•As a result of these anatomic abnormalities:

–The duplicated ureters may be seen extending a variable distance down to the urinary bladder.

–Obstruction of the upper pole moiety down to the bladder may be seen, often associated with a ureterocoele.

–Vesicoureteral reflux into the lower pole moiety may be seen. This is often due to distortion in its insertion by an associated ureterocoele.

–Ectopic insertion of the upper pole moiety e.g. into the prostatic urethra in males or vaginal vault in females.

–If reflux is significant, evidence of reflux nephropathy may be evident.

6.4.3Clinical Features

•Most duplicated systems are asymptomatic and diagnosed incidentally.

•Duplex collecting system may be complicated by infection, vesicoureteral reflux or obstruction.

•Occasionally, hydronephrosis can be severe enough to result in flank discomfort, pain or even a palpable mass.

Classification of Duplex Collecting System

•Duplex kidney: Two separate pelvicalyceal system draining a single renal parenchyma.

•Duplex collecting system: A duplex kidney draining into:

–A single ureter: Duplex kidney with pelvicalyceal system uniting at the pelviureteric junction.

–Bifid ureters: Two ureters that unite before emptying into the urinary bladder.

–Double ureters (Complete duplication)

•Bifid collecting system: A duplex kidney with the two separate pelvicalyceal collecting system uniting at the pelviureteric junction or as bifid ureters (Incomplete ureteral duplication).

•Double/Duplicated ureters: Two ureters that drain separately into the urinary bladder or genital tract (Complete ureteral duplication).

•These are seen in patients with completely duplicated ureters.

•Duplication can be variable.

•At one end of the spectrum, there is merely a duplication of the renal pelvis, draining via a single ureter.

•At the other extreme, two separate collecting systems drain independently into the bladder or ectopically.

•Duplex systems may be unilateral or bilateral and can be associated with a variety of other congenital abnormalities of the urinary tract.

•Duplex systems can be associated with Fanconi anemia.

6.4.4Investigations

•Intravenous urography (IVU) (Figs. 6.14 and 6.15):

–This can demonstrate both collecting systems, but a poorly functioning system may not excrete contrast and will not be visualized.

–In such a situation, the functioning lower pole moiety will be inferiorly displaced,

taking on the so-called “drooping lily appearance”.

–This may be confused with an upper pole mass or cyst.

–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.

•Abdominal and pelvic ultrasound:

–Ultrasound is useful when the duplex system is associated with obstruction/ hydronephrosis.

–Ultrasound is also useful in detecting associated ureterocele.

–With the use of ultrasound it may be difficult to differentiate between partial and complete duplication.

–The duplex kidney appears as two central echo complexes with intervening renal parenchyma.

–Hydronephrosis at one pole is suggestive of a duplex kidney.

–Although hydronephrosis can occur at either pole, it is more common in the upper pole.

–Occasionally, two distinct collecting systems and ureters can be observed on ultrasonographic images.

–Differentiating an atrophied lower pole moiety of a duplex kidney (nubbin) from other renal masses is difficult.

–The nubbin of tissue from the atrophied lower pole of a duplex kidney cannot be confidently differentiated from other masses.

•CT urography:

–CT urography is able to delineate essentially all duplex abnormalities especially if reconstruction images are made.

–The intervening renal parenchyma in a duplex kidney lacks a collecting system and major vessels, and because of this it is described as having a “faceless kidney” appearance.

–A duplicated renal collecting system can be suspected if a faceless kidney is identified.

–CT scan can help to determine if an obstruction exists and can aid in assessing the renal parenchyma thickness.

–CT scan can also help to determine if the insertion of the duplex ureter is intravesical or extravesical.

–CT scan can demonstrate the collecting system in the nubbin or the mass effect of tissue at the pole.

–CT scan is superior to ultrasonography and excretory urography in diagnosing the lower pole nubbin.

•Nuclear scan:

–Renal scintigraphy is useful to evaluate renal function, particularly when planning corrective surgery.

–Renal scintigraphy is less useful to identify non-obstructed duplex systems.

–Duplex kidneys appear as two 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.

–The presence of a duplex kidney and ureteral duplication, suggested by 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.

•MR urography (Figs. 6.16, 6.17, 6.18, and 6.19):

–This may be used as a primary diagnostic method in assessing a duplex ectopic ureter and complications associated with duplex kidneys.

•An ectopic ureter extending from a poorly functioning moiety of a duplex kidney, invisible on other imaging, may be observed with MR urography

•Micturating cystourethrography:

–The intravesical ectopic ureter of a nonvisualized moiety is better demonstrated using voiding cystourethrogram.

–In patients with hydronephrosis, antegrade pyelography is useful for demonstrating the presence of a second ureter and for determining the level of termination.

6.4.5Treatment and Prognosis

•An asymptomatic duplex kidney usually does not require any treatment.

•Surgical treatment is indicated in the presence of complications.

•These complications include:

–Vesicoureteral reflux into lower pole moiety

–Marked hydronephrosis of the upper pole moiety may have mass effect or become infected

•Antibiotic prophylaxis is given to newborns with hydronephrosis or in patients who present with urinary tract infection (UTI) until the diagnosis is made and reflux is ruled out.

•Antibiotic prophylaxis is often continued in patients with obstructed systems and in infants with dilated nonobstructed systems.

•Duplicated collecting systems with reflux are managed conservatively with antibiotic prophylaxis until the reflux spontaneously

resolves or until the child is older (6–12 months), at which time surgery may be more easily accomplished.

•In infants with duplicated systems and a wellfunctioning but obstructed upper-pole moiety or an obstructed ectopic single-system ureter, urinary diversion (A cutaneous ureterostomy) may be the treatment of choice until the bladder

is bigger and a ureteral reimplantation with or without ureteral tailoring is more feasible.

•In infants with a duplicated system and no reflux is present in the lower-pole system, a ureteroureterostomy is an option.