Laboratory Studies
Rarely, bilateral renal dysplasia or significant renal scarring may be present, resulting in impaired renal function. In this scenario, renal function and electrolyte levels must be monitored. These patients must also be assessed for hypertension.
Ultrasonography
Antenatal fetal ultrasonography (US) is often the initial study suggesting the diagnosis on the basis of hydroureteronephrosis. The natural history of antenatally diagnosed duplication anomalies is that approximately half of these infants develop urinary tract infection (UTI), and about 25% require surgical intervention in the first few years of life. [2]
Postnatal abdominal US is the best initial screening study.
Renal measurements in duplicated collecting systems are often longer than those of a contralateral nonduplicated system (see the image below).
Renal duplication. Marked upper pole hydronephrosis with minimal dilation of lower pole, indicative of a duplicated collecting system.
Disparate hydronephrosis in the upper and lower pole of a kidney suggests ureteral duplication, especially with upper-pole dilation associated with an obstructed or ectopic ureter or with a ureterocele. (See the image below.)
Female infant with acute pyelonephritis. The ultrasonography findings are notable for left hydronephrosis.
A ureterocele can usually be seen at the bladder level and appears as a well-defined cystic intravesical mass that can be proximally followed into a dilated ureter (see the inage below). If the bladder is decompressed, visualization of a ureterocele is more difficult.
Bilateral ureteroceles with stones. This ultrasonogram at the bladder level depicts thin-walled, bilateral ureteroceles. Echogenic stone material can be seen in the left ureterocele.
US provides imaging for gross evaluation of the renal parenchyma. Increased echogenicity and renal cysts are sonographic signs that suggest renal dysplasia.
Virtual sonographic cystoscopy appears promising as a noninvasive means of evaluating ectopic ureterocele in children. [3]
Pyelography
Intravenous pyelography (IVP) is not commonly used. It generally reveals duplicated collecting systems and their level of confluence. In young girls with persistent incontinence, IVP may be helpful in defining ureteral anatomy and the level at which an ectopic ureter may be found. Typically, a ureterocele has been described as having a "cobra head" or "spring onion" configuration at the bladder level. Stones that collect in the ureterocele (see the image below) may be visible on the scout film.
Bilateral single-system ureteroceles. The collecting systems and their associated ureteroceles are opacified on intravenous pyelography (IVP). Multiple stones in the ureteroceles may be discerned within the ureteroceles (white arrows) as filling defects.
Because duplicated systems generally have poorly functioning renal moieties associated with ectopia or ureteroceles, these distinct images are usually observed with single-system intravesical ureteroceles. Delayed images are helpful in identifying poorly functioning renal units.
Retrograde pyelography (see the image below) can define the ureteral anatomy, and puncture of the ureterocele with instillation of contrast may aid in defining the origin of the lesion.
Single-system ectopic ureter. A retrograde pyelogram of the ectopic ureter opacifies the dilated system. The ureter is obstructed when the sphincter is closed but opens to drain when the sphincter opens during voiding.
Voiding Cystourethrography
Duplicated collecting systems with lower-pole reflux can be visualized by means of voiding cystourethrography (VCUG). The configuration of the kidney lacks opacification of the nonrefluxing upper pole, giving it the appearance of a "drooping lily" (see the image below).
Reflux into lower pole: A voiding cystourethrography (VCUG) that demonstrates reflux into the lower pole ureter with classic "drooping lily" configuration.
Ectopic ureters generally do not reflux unless they are ectopic to the bladder neck. In this case, the refluxing unit opacifies only during voiding, when the bladder neck is open. Occasionally, the radiologist may inadvertently pass a catheter transurethrally up the ectopic ureter. The initial films then opacify only that collecting system and not the bladder.
Ureteroceles are best imaged at initial filling and appear as a filling defect in the bladder base (see the image below). Identifying which side large ureteroceles are associated with can be difficult. Reflux of the ipsilateral lower pole is observed in approximately 50% of cases. Contralateral reflux may be observed in 25% of cases, and reflux into the ureterocele may be observed in 10% of cases.
A large ureterocele is seen as a filling defect on the early filling images of this cystogram.
Renal Scintigraphy
Mercaptotriglycylglycine (MAG-3) renal scintigraphy is the renal scan most commonly obtained to evaluate relative renal function and drainage. It provides information on segmental renal function, allowing comparison of the upper-pole moiety to the lower-pole moiety (see the image below). It may aid in the determination of salvageability and selection of operative technique. MAG-3 furosemide renography may also quantitate the degree of obstruction in moieties with preserved function.
Left duplicated kidney with upper pole ureterocele. This renal scan shows the typical findings of an upper pole duplicated system subtended by a ureterocele. The left upper pole (black arrow) shows minimal uptake when compared with the left lower pole or right kidney.
Technetium-99m (99mTc) diethylenetriaminepentaacetic acid (DTPA) is similar to MAG-3 but is less efficacious in patients who have kidneys with poor function and in newborns because of their relatively impaired glomerular filtration rates. Radiation exposure is fairly high with this compound.
99mTc dimercaptosuccinic acid (DMSA) is an agent that is taken up by the renal tubular cells and is used for renal scintigraphy. [4] DMSA resting can be used reliably to assess renal function but is not useful in evaluating urinary drainage of the upper urinary tract because it is secreted slowly into the urine.
CT and MRI
Axial imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is rarely the initial study of choice. In one study, contrast CT was the most reliable study in demonstrating the poorly functioning upper-pole renal moiety and the associated ectopic ureter causing continuous drip incontinence. [5]
Gadolinium-enhanced MRI may be valuable in opacifying an ectopic ureter that causes incontinence in a female, whereas other studies may not be diagnostic. A retrospective study by Ji et al suggested that antenatal MRI can be effective for diagnosing fetal duplex kidney deformity and associated ureteral and other abnormalities. [6]
Cystoscopy
Although sometimes used as an investigative modality, cystoscopy is usually performed during surgical intervention to verify the diagnosis. (See the image below.)
The search for the orifice of an ectopic ureter may be extremely difficult. Tedious probing of any small dimple along the urethra or anterior vaginal wall with a whistle-tip catheter may be rewarded with visual confirmation of the offending moiety upon the retrograde injection of contrast. The use of indigo carmine or methylene blue injected intravenously may help in locating an ectopic ureteral orifice at the time of cystoscopy.
Findings with large or ectopic ureteroceles, which can distort and obscure the entire field of vision, can be confusing. Finding the ureterocele orifice may be challenging.
Small ureteroceles may not be evident, especially when the bladder is distended, which causes the ureterocele to flatten or evert. When associated with duplication, large ureteroceles may obscure visualization of any ipsilateral ureteral orifice.
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Ectopic ureter. Cystoscopic view of an ectopic ureter entering the bladder neck.
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Single-system ectopic ureter. A retrograde pyelogram of the ectopic ureter opacifies the dilated system. The ureter is obstructed when the sphincter is closed but opens to drain when the sphincter opens during voiding.
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Ectopic ureter to urethrovaginal septum. This patient presented with continuous drip incontinence. The blue catheter is positioned in the urethra. The gray catheter is positioned in the orifice of the ectopic ureter.
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Duplicated ectopic ureter to the urethrovaginal septum. Retrograde injection of contrast into the orthotopic lower pole (white arrow) ureteral orifice and ectopic upper pole (black arrow) orifice simultaneously opacifies both systems.
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A large ureterocele is seen as a filling defect on the early filling images of this cystogram.
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Bilateral single-system ureteroceles. The collecting systems and their associated ureteroceles are opacified on intravenous pyelography (IVP). Multiple stones in the ureteroceles may be discerned within the ureteroceles (white arrows) as filling defects.
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Bilateral ureteroceles with stones. This ultrasonogram at the bladder level depicts thin-walled, bilateral ureteroceles. Echogenic stone material can be seen in the left ureterocele.
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Left duplicated kidney with upper pole ureterocele. This renal scan shows the typical findings of an upper pole duplicated system subtended by a ureterocele. The left upper pole (black arrow) shows minimal uptake when compared with the left lower pole or right kidney.
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Renal duplication. Marked upper pole hydronephrosis with minimal dilation of lower pole, indicative of a duplicated collecting system.
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Reflux into lower pole: A voiding cystourethrography (VCUG) that demonstrates reflux into the lower pole ureter with classic "drooping lily" configuration.
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Female infant with acute pyelonephritis. The ultrasonography findings are notable for left hydronephrosis.
